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Two pilot scale experiments investigating the one-step synthesis of methyl isobutyl ketone (MIBK) from acetone and hydrogen were conducted via catalytic distillation (CD) utilizing a Pd/Nb 2 O 5 /SiO 2 catalyst at a reaction temperature of 160 °C and system pressure of about 1.4 MPa. Moisture analysis of liquid samples extracted about the major axis of the CD column revealed that when the reactor was initially operated at 100% reflux as suggested in the patent of Lawson and Nkosi, water had accumulated in the top half of the reactor as evidenced by water concentrations of 9.4 and 21.0 wt% in the reactive and rectification sections respectively, resulting in the suppression of the DAA dehydration reaction and consequently a relatively low MIBK productivity. However, operation of the CD column at 83–97% reflux enabled the rapid in situ separation of water from the reactive section via the overhead distillate stream, which directly resulted in increases in the MIBK productivity and the hydrogen uptake efficiency by factors of about 20. This result demonstrates a unique advantage of CD technology, whereby a substantial kinetic enhancement may be realized from the selective in situ separation of a kinetically relevant inhibiting substrate from the reactant mixture. MIBK in excess of 50 wt% was observed in the reboiler product during this mode of operation, which is significant since state of the art processes for MIBK production typically yield less than 30 wt% MIBK in the reactor effluent. The reboiler product was found to be essentially moisture free, which is also significant since MIBK and water are known to produce azeotropic mixtures resulting in difficult and costly downstream separations. An experiment was conducted to study the effects of the hydrogen and reflux flow rates on the MIBK yield. The CD process for MIBK synthesis was found to be controlled by the rate of external mass transfer of hydrogen. The results indicate that the catalyst wetting efficiency affects the catalytic hydrogenation as evidenced by an increase in mesityl oxide conversion with decreasing reflux flow rate. This suggests the catalyst wetting efficiency is an important design criterion for this process. CD reactor bottoms product composition as a function of time-on-stream (TOS). Conclusion Operating the CD reactor under conditions of total reflux as described in the patents of Lawson and Nkosi resulted in the suppression of the DAA dehydration reaction due to the accumulation of water in the reactive section. Changing the mode of operation after condition #1 to include an overhead distillate stream, resulted in the rapid removal of water from the reaction section and the enhancement of both the catalyst activity and the hydrogen uptake efficiency by a factor of 20, enabling a moisture free MIBK product in excess of 50 wt%, which is an advancement in the state of the art. [Display omitted] • Catalyst activity was enhanced by a factor of 20 via the in situ removal of a kinetically relevant inhibiting substrate. • Catalyst wetting efficiency is a key reactor design consideration. • Mesityl oxide and MIBK syntheses are governed by competing transport processes. [ABSTRACT FROM AUTHOR]

Long-chain α-olefins (≥ C 10) are normally applied in detergents, lubricants, and oil field chemicals. Due to the abundance of palm oil, the derivatives derived from palm oil, such as oleic acid (OA), can be converted to long-chain olefins via oxidative dehydrogenation (ODH) over a series of vanadium oxides (V x O y) incorporated with KIT-6 (nV-KIT-6 catalysts) synthesized by a direct hydrothermal method. Various ammonium metavanadate/tetraethyl orthosilicate molar ratios (V/Si) were evaluated over the range of 0.01–0.09. The results obtained from X-ray diffractometry, hydrogen-temperature programmed reduction, and X-ray photoelectron spectroscopy analyses revealed that the V x O y were mainly in a tetrahedral form when the V/Si molar ratios were lower than 0.05. Above this point, the formation of V 2 O 5 crystallites was observed. The ODH of OA was performed in a continuous flow fixed-bed reactor under atmospheric pressure in the absence of solvent to avoid the interference of by-products generated from solvent oxidation. The results showed that the OA conversion and selectivity towards the desired products strongly depended on the V/Si molar ratio and the reaction temperature. The highest selectivity of olefins (alkenes + dienes) with carbon atoms in the range of C 7–17 was 44%. Moreover, the selectivity to aromatics at 24% was observed at a 76% OA conversion level when the ODH was activated using the 0.05 V-KIT-6 catalyst under a 1/1 (v/v) oxygen/nitrogen gas mixture at a flow rate of 100 mL min−1 at 450 °C. Although the high selectivity towards alkenes was promoted by a higher dispersion of V x O y species on the catalyst, overdose of V/Si molar ratios produced more oxygenate compounds. The reaction mechanism for the ODH of OA was likely to be decarboxylation and decarbonylation followed by dehydration. The 0.05 V-KIT-6 catalyst also exhibited reusability over two cycles. [Display omitted] • Ordered mesoporous nV-KIT-6 catalysts were synthesized by a one-pot hydrothermal method. • Highly dispersed V x O y species in a tetrahedral form were obtained at a V/Si molar ratio of < 0.05. • Long-chain olefins (≥ C10) were produced via the ODH of OA over nV-KIT-6 catalysts. • Olefin selectivity was strongly influenced by the V/Si molar ratio. • 0.05 V-KIT-6 catalyst showed the highest performance for giving the 44% selectivity to olefins (alkenes + dienes). [ABSTRACT FROM AUTHOR]

A highly active and selective mesoporous TiO 2 was developed by the sol-gel hydrolysis technique for the selective transformation of glucose to 5-hydroxymethylfurfural (5-HMF). The catalytic performance was tested in a glass tube reactor, and the reaction parameters were optimized using response surface methodology (RSM). The best-optimized reaction conditions were obtained using four-factors, four-responses, and the 5-level central composite design (CCD) integrated with the desirability approach. At the optimum reaction condition, RSM predicted complete conversion of glucose and a very high 5-HMF yield of ~56% in the dimethylsulfoxide (DMSO) solvent. The predicted yield of other major products, including formic acid (FA) and levulinic acid (LA), was ~18% and ~2%, respectively. The empirical process model developed by RSM was validated by the experimental data generated. Experimental results demonstrated that the TiO 2 catalyst developed can easily be recycled with a constant glucose conversion and 5-HMF yield. Further, a new liquid-liquid extraction method (LLE) is proposed to extract 5-HMF from the product. The results depicted that 5-HMF can easily be extracted from the product mixture with very high purity (~96%). Additionally, the Power-Law kinetic study suggested that the conversion of glucose over TiO 2 followed the first-order kinetics, and the calculated activation energy was 67.5 kJ mol−1. [Display omitted] • Highly selective and stable TiO 2 catalyst was developed for glucose dehydration. • Response surface methodology was used to optimize the reaction condition. • A maximum 5-hydroxymethylfurfural yield of 56% was achieved at ~100% conversion. • Glucose dehydration reaction followed the first-order Power-Law. • A new liquid-liquid extraction process is proposed for the separation of 5-HMF. [ABSTRACT FROM AUTHOR]

Kinetic models were developed for the vapor phase hydrogenolysis of glycerol in a fixed bed down flow tubular reactor over a highly stable bi-functional Cu-Zn/MgO catalyst. The kinetic experiments were conducted at atmospheric pressure, at different temperatures (200–220 °C), and contact time (W/F Go) (101.5–609 kgcat. h kmol−1), respectively. The Langmuir-Hinshelwood-Hougen-Watson (LHHW) and Eley-Rideal (ER) type kinetic models were tried considering a two-step glycerol dehydration-hydrogenation process. The model equations were solved in MATLAB by using the ode23 function and the kinetic parameters were optimized by using the genetic algorithm optimization technique. The activation energy for the dehydration and hydrogenation steps was found to be 57.73 ± 10 kJ/mol and 156.71 ± 10 kJ/mol from LHHW kinetic model and 82.6 ± 8.3 kJ/mol and 146.2 ± 3.9 kJ/mol from ER kinetic model, respectively. Results demonstrated that both the models were fitted very well with the experimental data generated. However, the parity plots of the simulated and experimental partial pressure of glycerol, acetol, and 1,2-PD suggested that ER model was more appropriate as compared to the LHHW model. [Display omitted] • A kinetic study on the vapor phase hydrogenolysis of glycerol was performed. • LHHW and ER kinetic models were developed. • The kinetic parameters were optimized by a genetic algorithm. • LHHW and ER model were fitted well with experimental results. • The energy barrier for dehydration was less as compared to hydrogenation. [ABSTRACT FROM AUTHOR]

The silanol groups present on the surface of lamellar silicates are excellent reaction sites for a varied number of chemical modifications. The conversion of these solids into zeolitic structures has shown to be an interesting synthetic alternative, once avoiding hard templating methods and producing materials with particular characteristics. In this work, a post-synthesis OSDA-free procedure was employed for the 2D–3D transformation of Na-RUB-18 lamellar silicate into mordenite zeolite. The conversion was performed at 140 °C and produced small zeolitic crystals (300–500 nm) after 12 and 24 h of crystallization. The reaction presented 65% yield (mol/mol SiO 2), producing materials with a similar Si/Al molar ratio (around 6). The 27Al MAS NMR spectra showed signals related to tetrahedrally coordinated aluminum. The N 2 adsorption/desorption isotherms confirmed the solids microporous nature and volume (0.36 and 0.43 cm3 g−1). The number of acidic sites was determined by NH 3 -TPD (976 and 848 µmol g−1), which also revealed sites with weak and moderate to strong acidity. Finally, the samples' catalytic activity was evaluated by the ethanol dehydration reaction performed at low temperature (150 °C). The synthesized materials were compared to a commercial sample and all the catalysts showed ethanol conversion around 70%, producing ethene and diethyl ether; the latter being the major product at the employed temperature. Unlike the commercial sample, the synthesized ones did not present any deactivation during the time on stream. This feature was attributed to their low-defect structure and subtle mesoporosity. [Display omitted] • Na-RUB-18 was used as precursor in OSDA-free hydrothermal conversion to MOR zeolite. • Small MOR crystals were obtained in high yield after 12 and 24 h of crystallization. • Low temperature ethanol dehydration reaction was performed over the MOR catalysts. • The synthesized MOR was twice as active as the commercial one in ethene production. • The low-defect/mesoporous structure was the key for superior catalytic activities. [ABSTRACT FROM AUTHOR]

A modified technique of epitaxial growth employed to produce "core-shell" catalysts coating microporous ZSM-5 with a layer of Silicalite-1 is presented in this paper. The aim was to passivate surface acidity of a ZSM-5 zeolite, in the view of potential limitation of surface effect generally responsible for coke formation. Core-shell catalysts have been synthesized starting from a ZSM-5 core with Si/Al = 25. Two different hydrothermal Silicalite-1 synthesis were performed: one using the ZSM-5 as made-form and the second using the ZSM-5H+-form as core. This allowed to investigate the effect of the organic template, filling the pores of the core, on the shell growth mechanism. Coating procedure lasted 24 h and it was repeated twice to increase Silicalite-1 thickness. All catalysts were tested for the reaction of methanol dehydration to DME in an atmospheric system at 180–240° and time on stream tests were carried out to analyse the stability of the samples. Considering the catalytic performances in terms of methanol conversion, DME selectivity and deactivation, core-shell catalysts, synthetized using an as-made form core, exhibited interesting performances, resulting from a more controlled growth of the passivating layer. These materials could constitute valid option for hybrid (Metal-Zeolite) catalyst, where the reduction of surface acidity could better stabilize the metallic function. [Display omitted] • Core-shell were synthesized using both an ZSM-5 as-made and an H+-form as core. • The empty pores of H+-form core caused a significant drop in physical properties after a the first deposition cycle of. • Acidity and acid sites strength of the core-shell samples depends on the core form. • Core-shell synthesis using an as-made core allowed to preserve pristine zeolite properties. • Performances in methanol-to-DME dehydration revealed the advantages of catalyst surface passivation. [ABSTRACT FROM AUTHOR]

Formic acid is a high-prospect energy carrier of sustainable H 2 and can also favorably supply sustainable H 2 to hydrogenation catalysts in replacement of external pressurized H 2. A solar photon-assisted synthesis method was successfully implemented for decorating a ceria-modified TiO 2 support with ultra-dispersed Ru nanoclusters with a large fraction of low atomicity species and Ru single atoms. Adding ceria to the TiO 2 support at a quarter of the theoretical monolayer is a suited surface modification for partially reducing the detrimental intrinsic activity of the bare TiO 2 surface for the dehydration of formic acid, what allows the undesired formation of CO to be mitigated and higher selectivities to H 2 to be achieved when using the Ru/CeO 2 /TiO 2 catalyst. The dual (combined) photonic/thermal excitation of the Ru/CeO 2 /TiO 2 catalyst boosted the H 2 production rate and allowed the dehydrogenation reaction to be conducted at a lower temperature compared to the dark conditions, for instance with a 80°C downshift at 190°C, what corresponded to a 42 % relative gain compared to the dark conditions. Advanced electron microscopy characterization has been crucial to unveil the atomic-level nature of the Ru/CeO 2 /TiO 2 photo-thermo catalyst, bringing to light the presence of ultra-dispersed metallic Ru nanoclusters, both (i) decorating nanometric-sized flat CeO 2 nanoparticles interfaced in epitaxy with high-index TiO 2 facets, and (ii) being homogeneously distributed over the TiO 2 surface in close vicinity with low atomicity CeO 2 species. [Display omitted] • CeO 2 nanoparticles and clusters electronically modify TiO 2 surface. • Advanced electron microscopy reveals Ru single atoms and clusters. • Ru/CeO 2 /TiO 2 catalyst outperforms Ru/TiO 2 reference in dehydrogenation reaction. • Ceria-based nanostructures partially inhibit CO formation, boosting H 2 selectivity. • Dual photonic/thermal excitations improve the HCOOH decomposition. [ABSTRACT FROM AUTHOR]

The implementation of increasingly stringent environmental regulations has increased the demand for more active catalysts in hydrotreating. This study proposes the synthesis, characterization, and evaluation of bimetallic NiMo catalysts supported on TiO 2 -Nb 2 O 5 nanocomposites for dibenzothiophene hydrodesulfurization. Samples containing 3, 5, and 10 wt% Nb 2 O 5 were synthesized to examine the influence of Nb content on their catalytic activity and selectivity. Supports and oxidized catalysts were characterized using various techniques, including SEM-EDS, N 2 physisorption, powder XRD, UV–vis DRS, Raman spectroscopy, and H 2 -TPR, while sulfured catalysts were further characterized by XPS and HRTEM. NiMo/TiNb3 and NiMo/TiNb5 catalysts displayed propene and diisopropyl ether as the main products in the 2-propanol dehydration reaction. A correlation was observed between hydrogenating capabilities in the HDS and dehydration tests with the Nb loading, suggesting that an optimal combination of Lewis/Brønsted acid sites enhances the BP/CHB ratio. All Nb-containing samples exhibited superior activity compared to their Nb-free counterparts, as indicated by the higher values of the pseudo-first-order rate constants (k HDS), which were higher for the NiMo/TiNb3 catalyst. These results were also associated with the respective textural characteristics, metal dispersion, and species distribution. [Display omitted] • Unmodified and Nb-modified TiO 2 -supported NiMo catalysts were tested in HDS reactions. • The addition of Nb atoms alters the surface acidity and the ratio of Mo species. • Nb-modified catalysts exhibited higher activity and selectivity than the unmodified one. • The incorporation of Nb species creates new hydrogenation sites. [ABSTRACT FROM AUTHOR]

The impact of UV irradiation on the catalytic transformation of dihydroxyacetone molecule (DHA) has been investigated under inert atmosphere, medium pressure (5 Bars) and temperature (<=120°C) in presence of commercial anatase TiO 2 samples (UV100 and A100), rutile TiO 2 (R100) and mixture of anatase and rutile phase (P90). In absence of light, the main products formed are pyruvaldehyde and lactic acid whatever the temperature playing only a role on kinetic. Under UV irradiation, we highlighted their decomposition and the formation of new compounds, hydroxyacetone (HydA) in high concentration and acrylic acid (AcrAc) together with H 2 , CO 2 and acetaldehyde in gas phase and new condensation products. The higher the number of photons emitted, the greater the HydA and AcrAc formation highlighting the importance of light and especially of the (e-, h+) pairs generated by photocatalysis. Actually, whereas the formation of HydA and AcrAc is similar in presence of all TiO 2 samples containing anatase phase, these compounds are formed in low concentration in presence of TiO 2 rutile. Mechanisms of the formation of hydA and AcrAc under photocatalysis assisted by pressure and temperature were discussed considering the formation of H+ and reducing agent made possible thanks to simultaneous oxidation reaction occurring via h+ and or OH° [Display omitted] • Photocatalysis modify the products, PA and LA, formed by DHA hydrothermal process (P, T, UV/TiO 2). • Formation of hydroxyacetone and acrylic acid from DHA transformation under P, T and UV/TiO 2. • Reducing agent such as e- or H 2 at the origin of Hydroxyacetone formation. • Availability of e- favored by simultaneous h+ reaction. • Acrylic acid issue from dehydration of lactic acid (LA) thanks to formation of H+. [ABSTRACT FROM AUTHOR]

[Display omitted] • Porous carbon fibers catalysts were prepared by electrospinning of Alcell lignin. • The addition of H 3 PO 4 allows to obtain carbon fibers with acid character. • The catalysts show high activity and selectivity to dehydration products. • The catalysts show a high stability in the studied reaction condition. Porous carbon fibers catalysts have been prepared by electrospinning of Alcell lignin, a green carbon precursor, which could be obtained as by-product in wood-to-ethanol biorefineries. The addition of H 3 PO 4 , a well-known chemical activation agent, to the electrospinning lignin solutions, at different mass ratios and the use of different carbonization temperatures, between 500 and 1600 °C, were analyzed in order to obtain carbon fibers with a large variety of porosity and chemical surface properties. Isopropanol decomposition was used as a catalytic test. Phosphorus-containing carbon fibers showed acid character and high catalytic activity, achieving propylene selectivity of 100 % under inert atmosphere. However, the use of air atmosphere increases the isopropanol conversion but produces the formation of acetone, via oxidative dehydrogenation, at low temperatures (∼20 %). Ethanol and methanol decomposition were also evaluated in air stream for the most active phosphorus-containing carbon catalyst, showing improved alcohol conversions with minimal gasification of the carbon fibers. These results confirmed that phosphorus-containing carbon fibers prepared by electrospinning of lignin solutions were excellent catalysts for alcohol dehydration reactions. [ABSTRACT FROM AUTHOR]

[Display omitted] • A microkinetic model was developed for DME synthesis over H-zeolite catalyst. • The optimized structures and reaction energetics were obtained by MP2 calculations. • The pre-exponential factors were estimated by fitting the experimental data. • The dominant reaction pathway and the rate-determining step were found. In this study, the reaction pathways of DME synthesis by methanol dehydration over a H-zeolite catalyst were analyzed through both computational chemistry and microkinetic modeling methods. The reaction mechanisms consisted of nine forward and backward elementary-step reactions for both associative and dissociative pathways. Based on the second-order Møller–Plesset perturbation theory (MP2), to determine the effects of dispersion forces that were important in our reaction system, the structures of all related reaction species were optimized, and the transition states of the associative and dissociative pathways were elucidated. Also, the energies and activation barriers of the optimized structures and transition states were calculated. Then, a microkinetic model was developed using the energies and activation barriers obtained from the MP2 calculations. Meanwhile, the pre-exponential factors of the kinetic parameters were not calculated theoretically but estimated by fitting the experimental data, which enhanced the reliability of the microkinetic model. By comparing the relative elementary-step reaction rates calculated using the developed model, the dissociative pathway was suggested as a dominant pathway of DME synthesis, while the DME formation reaction of the dissociative pathway (CH 3 OH-CH 3 -Z → CH 3 OCH 3 -H-Z) was found to be the rate-determining step. The developed model was also used to evaluate the effects of temperature on the site fractions over the catalyst. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ni 3 P, Ni 12 P 5 and Ni 2 P phases, identified by XRD and XAFS, are selective towards 1-propanol. • The presence of AlPO x and NiPO x species, determined by XAFS, increase the surface acidity. • Yield to 1-propanol decreases when surface acidity is higher than 1.3 × 103 mmol m−2. • With high surface acidity, selectivity towards 1-propanol decreases due to the formation of lateral dehydration products. The aim of this work was to investigate the catalytic properties of nickel over a carbon-based support modified with phosphorus for the hydrogenolysis of glycerol to obtain 1-propanol. For this, a series of nickel phosphide catalysts with different compositions were prepared employing Al(H 2 PO 4) 3 and NiCl 2 supported on mesoporous carbon and characterized by N 2 adsorption-desorption, acid-base properties measurements, TEM, XRD and XAFS analysis. These Ni catalysts presented different phases (Ni x P y , NiPO x , AlPO x), responsible of the increase in surface acidity, which depended on the Al(H 2 PO 4) 3 content. For Al(H 2 PO 4) 3 contents between 4 and 10 wt.%, an increase in surface acidity occurs that favors both the conversion and the selectivity of glycerol towards 1-propanol. These results show that the presence of the phosphates is necessary to reach high levels of catalytic activity. However, for Al(H 2 PO 4) 3 contents higher than 10 wt.%, a fall or loss of selectivity was produced due to the strong contribution of dehydration reactions on the support acid sites. The Ni/CPAl(10) catalyst, allows reaching 97 % conversion of glycerol with a selectivity of 74 % towards 1-propanol, employing an 80 wt.% glycerol aqueous solution, after 6 h of reaction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Niobia-based magnetic nanoparticles (MNP) coated with Nb 2 O 5 or Nb 2 O 5 -SiO 2 shells were prepared. • Prepared catalysts may produce HMF selectively by glucose dehydration. • High selectivity to HMF was correlated to pseudohexagonal niobium oxide (TT-Nb2O5) phase. • High catalytic activity was correlated to the small nanoparticles size. Niobia-based magnetic nanocomposites were prepared by covering magnetite nanoparticle cores (Fe 3 O 4 , MNP) with either Nb 2 O 5 or Nb 2 O 5 -SiO 2 shells using a two-step procedure. In the first step magnetite nanoparticles were prepared by the coprecipitation method. The second step involved their coverage with either Nb 2 O 5 shells, through a precipitation method, or with Nb 2 O 5 -SiO 2 shells, through a sol-gel protocol followed by precipitation in the presence of the CTAB surfactant. The obtained materials were exhaustively characterised by X-ray diffraction, Mössbauer spectroscopy, magnetic measurements, ICP-OES, DRIFT and Raman spectroscopy, and CO 2 - and NH 3 -TPD measurements, and investigated for glucose dehydration to HMF. The catalytic performances were directly correlated to the nature of the supported niobia phases, which, in turn, has been dictated by the niobia content and the preparation route. The high selectivity to HMF was correlated with to the large pseudohexagonal niobium oxide (TT-Nb 2 O 5) phase while the catalytic activity was directly correlated to the small nanoparticles size. A proper combination of these features led to an optimum catalytic system for the selective production of HMF through glucose dehydration. A third important feature making the developed catalyst promising is its magnetic property, ensured by the magnetite nanoparticles core. This allowed its easy separation from the reaction products. [ABSTRACT FROM AUTHOR]

[Display omitted] • Dehydration of ethanol was studied over silica-supported HPCs between 200 and 350 C°. • The XP spectra show that Pd doped HPAs consists of Cs3PW crystallites coated with Pd0.25 P W layers. • The value of Brönsted acidity has a significant impact on the coke formation. • Pd and SBA-15 improves the catalytic activity by reducing the catalysts deactivation. • After air regeneration, the catalysts regain the catalytic activity for o short time. The pure and palladium doped 12-tungstophosphoric acid - H 3 PW 12 O 40 (HPW) and its cesium salts Cs x H 3-x PW 12 O 40 (x = 1, 2, 2.25 and 2.5) were prepared and characterized by thermal analysis, FTIR, XRD, BET and XPS methods. In this paper were determined the optimal reaction temperature and the effect of palladium on the coke content during the dehydration of ethanol in the temperature range of 200−350 °C. Above 300 °C, a strong deactivation of the catalysts was caused by coke formation. The catalytic tests demonstrate that by supporting the HPW and Pd y PW (y = 0.15, 0.2 and 0.25) on mesoporous molecular sieve SBA-15 the catalytic activity in ethanol dehydration reaction was improved. Palladium doping of HPW/SBA-15 significantly decreases the formation of coke deposit. The formation of coke during the ethanol dehydration does not affect the Keggin structure which led us to conclude that such catalysts can be regenerated in air and regain their catalytic activity for a short time. [ABSTRACT FROM AUTHOR]

[Display omitted] • Functionalised nanographitic carbon is active in the fructose dehydration reaction to 5-HMF. • HMF yield can be adjusted by changing the reaction parameters. • Sulfonated carbons have the best activity/selectivity balance, being p -toluenesulfonic activated sample the best one. • The samples is stable under recycling in terms of HMF selectivity. A series of functionalized nanographitic carbons is prepared, characterized and tested in fructose dehydration reaction to 5-hydroxymethylfurfural. The functionalization treatment was selected to introduce various Brönsted acid sites and to modify the textural and catalytic properties of the initial carbon material. Within the series, the sulfonated carbons present the most interesting catalytic behavior resulting in important selectivity to the desired product once the reaction variables were properly adjusted. [ABSTRACT FROM AUTHOR]

[Display omitted] • Shift from sulfuric acid catalysts to novel solid acid foam catalyst for the continuous synthesis of furfural • Solid acid foams as catalyst and liquid-liquid contactor for synthesis and in-situ extraction of furfural: high yield, minimal residence time, and stable performance. • Novel and reproducible procedure to deposit stable sulfonic resins on foam structure. This paper demonstrates the use of sulfonated foam structures, acting both as catalyst and liquid-liquid contactor, during the continuous dehydration of xylose to furfural in biphasic media. First, we develop and optimize a coating procedure comprising a two-step polymerization technique (polypropylene and polystyrene-divinylbenzene), followed by swelling and sulfonation. The method was highly reproducible and led to a stable, well-adhered, 12–50 μ m layer of sulfonic resin with an ion exchange capacity of 0.1 meq/cm foam 3. The catalytic foams showed the same activity than H 2 SO 4 in terms of conversion and selectivity versus residence time and temperature. The enhanced mass transfer properties of the foam-based reactor facilitated rapid furfural extraction, thus allowing for higher temperature operations (ca. 20–50 ° C higher) and shorter residence times (ca. 10 min vs. 4–5 h) than conventionally reported in the literature, while preserving high furfural selectivity (ca. 70–80%). Finally, the stability of the sulfonated foam catalyst during operation was demonstrated up to 170 ° C, although higher temperatures led to a visible decay in activity. We conclude that the sulfonated foams show great potential for this application. [ABSTRACT FROM AUTHOR]

MgO-La 2 O 3 catalysts with different Mg/La molar ratio were synthesized by a precipitation method and a subsequent calcination and then characterized by x-ray diffraction, N 2 adsorption-desorption isotherms (at −196 °C), CO 2 - and NH 3 -thermoprogrammed desorption and x-ray photoelectronic spectroscopy. The coexistence of acid and basic sites promoted the selective transformation of ethanol into valuable products. Thus, MgO catalyst promoted the Guerbet reaction obtaining n -butanol as product while the incorporation of La 2 O 3 in the catalytic system improved the ethanol conversion notably, obtaining ethylene as the main product due to a dehydration reaction. The highest ethylene yield was obtained for the catalyst with a Mg/La molar ratio of 1. [Display omitted] • The coexistence of acid and basic sites promotes the selective transformation of ethanol. • MgO catalyst promotes the Guerbet reaction obtaining n -butanol as main product. • The presence of La 2 O 3 in Mg-La-O catalysts improves the ethanol conversion to ethylene. • The highest ethylene yield was obtained for the catalyst with a Mg/La molar ratio of 1. [ABSTRACT FROM AUTHOR]

The sustainable chemistry based on acid-catalysed alcohol conversion reaction is a promising route to contribute to the de-fossilization strategies completion. In this concern, C1 and C2 alcohols are both well recognised sources for the production of ethers and olefins from sustainable sources in acid catalysed dehydration reaction pathway. Most of the literature is devoted to the investigation of pure alcohols conversion, whilst the simultaneous dehydration of alcohol in mixture can broad the product panel (contributing to the enlargement of bio-alcohols based chemistry) also elucidating the role of acidity (type and distribution) on the reaction mechanism. This paper is the first contribution analysing the role of acid sites (amount and distribution) on the simultaneous methanol/ethanol dehydration using ZSM-5 zeolites. ZSM-5 materials with different aluminium content were synthesised and used in catalytic test. The obtained results showed how Lewis acid sites are less important when dealing with ethanol (also in mixture with methanol) and how the different methylated- ethylated species formation can affect the product composition and the coke amount and composition. [Display omitted] • ZSM-5 with a different Si/Al in the range 11–50 were successfully synthesised. • Simultaneous methanol/ethanol dehydration was assessed. • Methyl ethyl ether is mainly produced at low temperature. • Methoxy species formation is inhibited in presence of ethanol. • No ethyl-substituted aromatics are formed during MeOH/EtOH simultaneous conversion. [ABSTRACT FROM AUTHOR]

• Al 2 O 3 -Ga 2 O 3 solid solutions were obtained and resulted in high activity. • The Pd deposited resulted in metallic nanoparticles highly dispersed. • Gallium oxide content impact directly on the dehydration activity and selectivity. • The morphology of Pd nanoparticles resulted Ga 2 O 3 content dependent. • The highest activity among series was observed over the Pd/AlGa-50 catalyst. A series of mixed Al 2 O 3 -Ga 2 O 3 oxides were prepared with different Ga 2 O 3 content (labeled as AlGa-x; where x is the wt % of Ga 2 O 3) by precipitation method. The oxides were then used as supports of palladium (2 wt %) catalysts (labeled as Pd/AlGa-x). Both series of samples, AlGa-x and Pd/AlGa-x were characterized by several techniques such as Raman spectroscopy, XPS, XRD, SEM, and HRTEM, and were tested in the 2-propanol dehydration reaction. The steady-state conversions displayed by the Pd/AlGa-x series was almost twice as that obtained for the AlGa-x series in all the range of tested temperatures. It was worth noting that the presence of palladium changed the yield observed for the AlGa-x series mainly at low temperatures. While at high temperatures the Lewis acidity provided by the well dispersed Pd nanoparticles increased the activity considerably and improved the propylene production. A balance between the dispersion of palladium and the surface acidity, both related to the Ga 2 O 3 content was responsible for the observed catalytic behavior. [ABSTRACT FROM AUTHOR]

• Selective production of terephthalate from FDCA ester over heteropolyacids. • Silica-supported HPW is significantly more active than other supported HPAs. • Strong Brønsted acidity is a key to improving the selectivity toward terephthalate. • Terephthalate yield of ˜60% can be achieved by 25%-HPW/SiO 2. The Diels-Alder reaction of biomass-derived dimethyl 2,5-furandicarboxylate (DMFDC) with ethylene followed by dehydrative aromatization is a sustainable route for the production of terephthalic acid, a monomer used for the synthesis of polyethylene terephthalate (PET). In this work, a series of heteropolyacid (HPA) catalysts with different supports, in this case SiO 2 , TiO 2 and ZrO 2 , and hetero-addenda atoms, here phosphotungstic acid (HPW), silicotungstic acid (HSiW) and phosphomolybdic acid (HPMo), were used as catalysts, and their structure-activity correlation in the conversion of DMFDC to terephthalate was examined based on the density and strength of the acid sites. Characterization by XRD and Raman indicated that the Keggin structures of HPAs were well preserved on the SiO 2 support compared to other supports, resulting in strong Brønsted acidity. The silica-supported HPW and HSiW catalysts exhibited significantly higher activity for terephthalate production than other supports and HPMo catalysts, but their activity were not correlated with the total acidity as measured by NH 3 -TPD. In contrast, the catalyst acid strength, as determined by the NH 3 desorption temperature, decreased in the order HPW/SiO 2 > HSiW/SiO 2 >> HPW/ZrO 2 > HPW/TiO 2 > HPMo/SiO 2 and was well correlated with the turnover rate for terephthalate production, suggesting that the higher activity of HPW/SiO 2 is at least partly due to its stronger Brønsted acidity and that promoting the dehydration step of this reaction is a key to improving the selectivity to terephthalate. The effects of reaction conditions, in this case the acid loading amount, solvent used, temperature, and time, were also investigated with the most active silica-supported HPW catalysts to optimize the terephthalate yield. The 25%-HPW/SiO 2 catalyst demonstrated a remarkable terephthalate yield of ∼60% with almost complete conversion under the optimum condition. [ABSTRACT FROM AUTHOR]

• The biphasic reaction of oleic acid with glycerol is limited by diffusion. • Ester products act as phase transfer catalysts accelerating the reaction. • Ester formation is accompanied by oxidation/dehydration co-products. This work investigates two new aspects of the biphasic esterification reaction of glycerol (G) and oleic acid (A), i.e. the formation of several oxidation/dehydration co-products and the effect of the ester products as phase transfer agents to accelerate the reaction. Potentiometric titration, FTIR, TG and especially paper electrospray mass spectrometry (PS-MS) were employed to analyze the products. Reactions with different G:A molar ratios (1:0.5, 1:1 and 1:2) without catalyst at 140, 160 and 180 °C showed oleic acid conversions of 50–80% to form the mono, di and triesters with several other by co-products due to dehydrogenation/oxidation of the oleic chain and dehydration of the glycerol moiety identified by PS-MS. The phase transfer autocatalytic effect was investigated by the addition of the oleate esters (2, 4 and 10 wt%) to the reaction. It was observed a strong acceleration of at the initial stage of the process indicating an autocatalysis likely due to a phase transfer effect. The reaction is discussed in terms of three stages. In the initial biphasic Stage 1, oleic acid suffers some dehydrogenation/oxidation and the esterification reaction takes place slowly at the glycerol-oleic acid interface to form mainly the monooleate ester which is an amphiphilic/tensoactive molecule. In the Stage 2, the amphiphilic ester products act as phase transfer agents taking glycerol molecules to the oleic acid phase for the formation of mono and mainly dioleate ester. At the Stage 3 in the presence of relatively high concentration of the tensoactive ester products the reaction becomes homogeneous/monophasic. [ABSTRACT FROM AUTHOR]

Different metal halide catalysts supported on a commercial active charcoal have been synthesized, activated, characterized and tested in glucose dehydration to 5-hydroxymethylfurfural using a biphasic water/methyl isobutyl ketone media. The influence of the cation nature (K+, Ca2+, Sr2+, Mg2+) and anion nature (F-, Cl-, Br-) on the catalytic performance of the solid is discussed in terms of glucose conversion, HMF yield and products selectivity. The activation of the impregnated catalysts results in a great diversity of active sites, such as Bronsted sites (carboxylic groups), basic sites (metal oxide), and Lewis acid site (Mn+). Their distribution within the samples determinates the resulting products and the final HMF yield. [Display omitted] • Metal Halide catalysts supported on active carbon are active in the glucose dehydration to 5-HMF. • Cation (K+, Ca2+, Sr2+, Mg2+) and anion nature (F-, Cl-, Br-) affects the catalytic performance. • Thermal activation of the catalysts decreases the surface acidity and originates new active sites, such as MOx. • Activated catalysts shows higher glucose conversions and minor HMF selectivity than fresh ones. • The best performing catalyst is stable and maintains it activity during four cycles of reutilization. [ABSTRACT FROM AUTHOR]

Graphical abstract The one-pot production of HMF from glucose in biphasic water/MIBK solvent using Nb(0.02 and 0.05 mol%)-Beta zeolites occurs with a selectivity to HMF of 84.3% for a glucose conversion of 97.4%. Highlights • Niobium-Beta zeolites were prepared via a post synthesis methodology. • Efficient one-pot transformation of glucose to 5-hydroxymethylfurfural (HMF). • The catalysts are stable in hot water, at 180 °C. • Working in biphasic water/MIBK solvent improves the selectivity to HMF. Abstract The one-pot production of HMF from glucose was investigated in pure hot water and biphasic water/methylisobutylketone (MIBK) solvent using mesoporous Nb(0.02 and 0.05 mol%)-Beta zeolites obtained by a post synthesis methodology. The mesoporous Nb-Beta zeolites present residual framework Al-acid sites, extra-framework isolated Nb(V) and Nb 2 O 5 pore-encapsulated clusters in which Nb(V)O-H exhibit moderate strength Brønsted acidity. After optimization, the dehydration of glucose onto the Nb-modified Beta-zeolites occurred with a selectivity of 84.3% in HMF for a glucose conversion of 97.4%. This result has been obtained in a biphasic water/MIBK solvent and in the presence of NaCl, at 180 °C, after 12 h. [ABSTRACT FROM AUTHOR]

1-butanol dehydration reaction has recently emerged as a sustainable route to produce butenes which can be further oligomerized to be applied as jet fuel. However, the high catalyst deactivation rates observed during this reaction due to coke deposition is still a pending matter. As promising catalysts for this reaction, we have supported two heteropolyacids (HPA), i.e. H 4 SiW 12 O 40 (STA) and H 3 PW 12 O 40 (TPA), on two commercial carbon materials: an activated carbon (AC) and a high surface area graphite (HSAG). Aiming to evaluate the role of HPA-support interactions, the STA was also dispersed over metallic oxides of different acidic nature, namely SiO 2 , Al 2 O 3 and ZrO 2. An exhaustive physicochemical characterization revealed that after the HPA dispersion thorough the support, the Keggin structure was maintained and an increase in the amount and strength of acid sites was provoked, but in different degree according to the HPA type and support's nature. While the TPA-based catalysts developed less quantity of total acid sites, but higher strength than their STA-carbon counterparts, the STA/AC and TPA/AC samples exhibited a slight major amount of acid sites than STA/HSAG and TPA/HSAG. The HPA-support interactions have ultimately modulated to some extent the activity, selectivity, stability and regeneration ability of the synthesized catalysts, when applied in the gas phase butanol dehydration reaction at 275 °C. The higher STA decomposition temperature prompted by the graphitic support, among other factors, allowed the total regeneration of the highly active (39 mmol BuOH ∙min−1∙g a.p) and n-butenes selective (>98 %) STA/HSAG catalyst by means of combustion of carbon deposits at 400 °C. [Display omitted] • Two heteropolyacids, STA and TPA, are dispersed on supports of different nature. • The amount and strength of acid sites depend on the HPA type and support's nature. • HPA-support interactions modulate the catalytic performance in butanol dehydration. • The optimal HPA-support interactions are observed in the STA/HSAG catalyst. • STA/HSAG is the only regenerable catalyst through a proper coke oxidation treatment. [ABSTRACT FROM AUTHOR]

A fast and simple post-synthesis method for creating secondary mesoporosity in EMT zeolites was developed using an ammonium fluoride / cetyltrimethylammonium bromide (NH 4 F/CTAB) solution at low temperature with ultrasound irradiation. This strategy is shown to be highly effective for producing hierarchical EMT structured zeolites through the etching of both Si and Al species. The catalytic performance of these materials were assessed using glycerol dehydration as a reaction test, which is in addition a relevant reaction due to the high amounts of glycerol generated as a by-product of biodiesel production. The resulting hierarchical EMT structured zeolites exhibited improved catalytic activity and high selectivity towards acrolein (around 80 %). This innovative approach creates new opportunities for using hierarchical EMT structured zeolites in processes related with biodiesel manufacture. [Display omitted] • Simple and fast post-synthesis treatment to achieve hierarchical EMT zeolites. • NH 4 F/CTAB solution preserves the zeolitic framework getting narrower mesopores. • Mesoporosity/acidity synergism in hierarchical EMT promotes catalytic improvement. • Use of hierarchical EMT in glycerol dehydration was reported for the first time. • Hierarchical EMT structured zeolites show around 80 % acrolein selectivity. [ABSTRACT FROM AUTHOR]

This study investigated the use of 30 w/v% H 2 SO 4 sulfonated wood waste-derived biochar as catalysts for production of value-added chemicals from carbohydrates in water as an environmentally benign solvent. Physicochemical characteristics of the sulfonated biochar were revealed by Fourier transform infrared spectroscopy (FTIR), acid-base neutralization titration, gas adsorption analysis, thermogravimetric analysis (TGA), and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). Using the sulfonated biochar as catalysts, hydrolysis of maltose at 140–160 °C resulted in the maximum glucose yield of 85.4% and selectivity of 88.2%, whereas dehydration of fructose at 160–180 °C produced the maximum HMF yield of 42.3% and selectivity of 60.4%. A higher range of reaction temperature was required for fructose dehydration due to the higher energy barrier compared to maltose hydrolysis. While increasing the temperature accelerated the catalytic reactions, the maximum product selectivity remained unchanged in the sulfonated biochar-catalyzed systems. The products were stable despite the increase in reaction time, because rehydration and adsorption of products was found to be minor although polymerization of intermediates led to unavoidable carbon loss. This study highlights the efficacy of engineered biochars in biorefinery as an emerging application. [ABSTRACT FROM AUTHOR]

Several new solid oxo-rhenium and oxo-molybdenum catalysts were tested for the deoxydehydration (DODH) of 1,2-diols to terminal olefins employing aromatic solvents and reaction temperatures of 150–200 °C. A catecholato oxo-rhenium catalyst tethered to silica was prepared and found to have comparably high DODH activity to its soluble analog with triphenylphosphine as the reductant. Catalyst re-use and leach-test experiments show significant leaching into the liquid phase. Silica, ceria and, for the first time, alumina and iron oxide were tested as supports for perrhenate, with ceria producing the least active material in 1,2-decane diol DODH. Decene yields obtained with ReO x /SiO 2 , ReO x /Fe 2 O 3 , ReO x /Al 2 O 3 were highest when triphenylphosphine was the reductant and reached 70 − 78% (at 90–100% conversion) at 150 °C. These three catalysts were also effective with gaseous reductants H 2 or CO. Leaching of rhenium species occurred for all supports and was most pronounced for SiO 2 . New solid oxo-molybdenum catalysts were synthesized. At 200 °C, decene yields observed using MoO x /Fe 2 O 3 , MoO x /SiO 2 , MoO x /Al 2 O 3 , MoO x /TiO 2 and MoO x /ZrO 2 were comparable and did not exceed 20%. There were homogeneous contributions through leached molybdenum species. [ABSTRACT FROM AUTHOR]

Zeolite-catalyzed dehydration of ethanol is an attractive economically feasible route for production of ethylene and butenes. The goal of this contribution is to monitor the intermediate species on the surface of “working” catalyst to rationalize the influence of the reaction conditions and zeolite characteristics on the dehydration pathways. With this respect the rates of diethyl ether (DEE) and ethylene formation in ethanol dehydration along with the quantification of the surface-intermediates (ethanol monomer and dimer) were simultaneously assessed under different reaction conditions in H- MFI zeolite. The reaction conditions (pressure, temperature, and ethanol conversion) control the population of surface intermediates and hence determine the dominant reaction mechanism. The results support the prevalence of dimer-assisted etherification at high ethanol pressures and enhanced contribution of ethoxide-mediated route with increasing the temperature. At high conversion, the DEE decomposition route producing ethylene was confirmed for H- MFI at 488 K along with ethoxide-mediated pathway. [ABSTRACT FROM AUTHOR]

Phosphorus-modified Al 2 O 3 supports containing different P content were prepared to control the acidity of Ni-impregnated catalysts for application in the dry reforming of methane (DRM). Results from the H 2 -temperature-programmed reduction showed that an increase in P content promoted the formation of an AlPO 4 phase, and resulted in an increase in Ni particle size. Although the initial conversion of CH 4 and CO 2 decreased with increasing P content, the addition of P influenced on the acidic properties of the support and the catalyst. Indeed, a decrease in catalytic deactivation correlated with the decreasing acidity of the P-modified supports and the Ni/P-Al 2 O 3 catalysts, and the acidic properties were determined by the behaviors of the temperature-programmed desorption of iso -propanol (IPA) and the dehydration of IPA. We found that the Ni/Al 2 O 3 catalyst modified by 2 wt.% P exhibited the weakest acidity whilst demonstrating excellent coke resistance and stability over 100 h in the DRM reaction. [ABSTRACT FROM AUTHOR]

The present review aims at summarizing the scientific literature data and patents concerning the isobutanol, preferably from a fermentation process, selective dehydration reaction to produce isobutene (isobutylene). The benefits and drawbacks of the conditions used on the process design and catalyst performances are illustrated, analyzed and discussed with much objectivity. Thermodynamic equilibria of the various reactants and products are provided together with the limiting step rate. Isobutanol selective dehydration to isobutene can be done under low or high pressure conditions. This choice impacts not only the downstream recovery and purification of isobutene, but also the stability of the catalyst and the reactor volume. Due to the strong inhibition of the alumina catalysts by steam, the reaction under pressure requires longer contact times and catalyst volume. The alumina catalysts need to have a good hydrothermal stability to avoid a rapid deactivation. Isobutene purification is also addressed. The impact of the water partial pressure on the catalytic dehydration is described and shown to affect the side reactions. Mass transfer limitations and kinetics of the reaction are well documented. Relevant advices are provided to perform the reaction without undesired products. [Display omitted] • Dehydration can be done under low or high pressure conditions, which impacts the purification. • The reaction is inhibited by water adsorption. • The alumina catalyst surface has to be stabilized to avoid continuous reconstruction. • Isobutene final end-use determines the dehydration process conditions. [ABSTRACT FROM AUTHOR]

The oxidative dehydration of glycerol to acrylic acid can be performed in one single step using bifunctional catalysts containing both acid and redox sites. In this sense, zeolites containing transition metals are promising catalysts. Zeolites of different topologies: FAU, FER, MEL, MFI, MOR, MWW and OFF were synthesized and further impregnated with 5% vanadium. The catalysts were characterized and evaluated in the gas phase glycerol oxidative dehydration. All catalysts showed high conversions of glycerol (100-78%). The acrolein selectivity decreases with the total density of acid sites in these zeolites. The selectivity to acrylic acid is related to the ability of each topology of stabilizing the redox pair V 5+ /V 4+ . The best performances were observed for zeolite catalysts with MWW, BEA and MFI topologies. [ABSTRACT FROM AUTHOR]

Propylene is an important constituent of many products that we rely upon in our daily life. This essential raw material is currently produced from fossil-derived feedstocks such as oil and natural gas. However, conversion of bioethanol to propylene represents an interesting opportunity for the utilization of renewable feedstocks such as bioethanol as one of the main biomass-derived products via dehydration process. The catalytic production of propylene from bioethanol has gained significant attention recently as a renewable alternative to conventional technologies. This review will discuss the state-of-the-art on the use of catalytic materials, such as zeolites and transition metals, in catalytic conversion of bioethanol to propylene and related reactions. The corresponding mechanisms are reviewed with emphasis on the possibilities provided by these materials to develop alternative processes for selective production of propylene and other olefins from bioethanol. Important aspects such as catalyst texture and architecture, the impact of promoters and co-feeding water on ethanol to propylene reaction and fundamental understanding of reaction mechanisms involved in ethanol dehydration reaction are discussed accordingly. [ABSTRACT FROM AUTHOR]

Direct dimethyl ether (DME) synthesis from synthesis gas is studied with regard to potential effects of methanol dehydration on methanol formation and copper-based catalyst performance. For this, the influence of the operating conditions (space velocity, temperature, pressure, time-on-stream and syngas composition) on activity, selectivity and stability of the catalyst was studied and compared for methanol synthesis and direct DME synthesis. The advantage of the direct over the two-step DME synthesis is apparent at conditions where syngas conversion to methanol is thermodynamically limited. However, under the applied operating conditions, results suggest that combining methanol synthesis and dehydration has a negative effect on the methanol formation kinetics. The origin of the observed phenomena is investigated by varying dehydration catalyst and by introducing dehydration products (DME and water) into the methanol synthesis feed. Choice of the solid acid catalyst does not seem to affect methanol formation, and DME is also found to be practically inert over the methanol synthesis catalysts. Water injection, on the other hand, led to a significant decrease in the methanol synthesis rate. Thus, formation of an additional amount of water through methanol dehydration might be an explanation for the lower methanol formation rate in the direct DME synthesis. [ABSTRACT FROM AUTHOR]

Rb + - and Cs + -exchanged Beta zeolites (Rb x Na 1− x β and Cs x Na 1− x β) of varying exchange degrees ( x = 0–1.00) were employed to catalyze the gas-phase dehydration of lactic acid (LA) for sustainable production of acrylic acid (AA) in a flow fixed-bed reactor at 360 °C, using an aqueous solution of LA (10 mol% or 35.7%) as the reaction feed at a weight hourly space velocity by LA of 2.1 h −1 . An appropriate window of the ion exchange degrees for highly selective AA production (≥60 mol%) was determined for either series of the samples, i.e., x = 0.85–0.98 for the Rb x Na 1− x β and x = 0.71–0.90 for the Cs x Na 1− x β samples. The best performing catalysts Rb 0.95 Na 0.05 β, and Cs 0.81–0.90 Na 0.19–0.10 β offered the highest AA selectivity (ca. 70 mol%) and yield (ca. 60–65 mol%) for reaction periods of longer than 10 h. Measurements of the surface acidity and basicity of the catalyst samples by temperature-programmed desorption of NH 3 and CO 2 showed that the highly selective catalysts in such widows should have both weakly acidic and weakly basic surface sites with suitably balanced acidity and basicity. The acid-catalyzed decarbonylation/decarboxylation and base-catalyzed condensation of LA, which lead respectively to formation of acetaldehyde and 2,3-pentanedione, always occurred as the competing reactions over the investigated catalysts. Observations on the catalyst selectivity changes for these competing reactions clearly demonstrate that the suitably balanced acidity and basicity at the catalyst surface is the key to the high selectivity for the desired dehydration reaction. [ABSTRACT FROM AUTHOR]

A carbon-based solid acid catalyst was prepared via hydrothermal method using glucose as carbon precursors and aqueous solution of H 2 SO 4 as sulfonation agent. The as-synthesized solid acid catalyst was attempted in the catalytic dehydration of fructose to 5-hydroxymethylfurfural (HMF). The effects of acid site density, reaction time, solvents, catalyst amount, temperature and mole ratio of catalyst to substrate were investigated. Under the optimum reaction conditions, the HMF yield of 90% was achieved in dimethylsulfoxide (DMSO) solvent at 160 °C after 1.5 h reaction time duration. The solid acid catalyst can be separated from the reaction mixture after reaction and reused without substantial loss in catalytic activity. [ABSTRACT FROM AUTHOR]

In 0.1 M sulfuric acid at 125 °C, levulinic acid did not form humins, and if HMF was present, levulinic acid was not incorporated in the humins that formed from it. Levulinic acid was converted to unidentified products believed to include angelica lactones, at a rate more than 500 times smaller than the rate of HMF conversion. Quantum chemical calculations indicate that at reaction conditions, levulinic acid is protonated to form protonated dihydro-5-hydroxy-5-methyl-2(3H)-furanone which is very stable. Very small amounts of levulinic acid and 5-hydroxy-γ-valerolactone may be present in equilibrium with this cation. Angelica lactones can then be formed from 5-hydroxy-γ-valerolactone in an acidic aqueous environment. [ABSTRACT FROM AUTHOR]

W–V–Nb–O complex metal oxides having a structure like that of orthorhombic Mo 3 VO x were found to be an efficient catalyst for the gas-phase direct oxidative transformation of glycerol to acrylic acid. The catalysts with various compositions were facilely synthesized by hydrothermal method. The W–Nb–O catalyst without V component, mainly promoted the glycerol dehydration, giving acrolein selectively. Since Nb–O catalyst showed poor activity for the reaction, the introduction of W into the Nb–O catalysts was found effective for improving the activity for the dehydration of glycerol to acrolein. This is mainly due to the increase of Brönsted acidity by the combination of W and Nb. When V was incorporated into the framework of W–Nb–O, the resulting catalyst was found to prominently promote the formation of acrylic acid in the glycerol transformation in the presence of O 2 , while showed no effect on the dehydration of glycerol to acrolein. It was also found that V acts as an oxidation site only when glycerol is completely reacted. The optimum elemental composition for the reaction was W 2.2 V 0.4 Nb 2.4 O 14 giving ca. 46% one path yield of acrylic acid and this catalytic performance was further improved by the surface modification with phosphoric acid, achieving ca. 60% one path yield of acrylic acid. [ABSTRACT FROM AUTHOR]

The gas phase dehydration of glycerol to acrolein over a series of supported silicotungstic acid (HSiW) on zirconia (10HZ, 20HZ, 30HZ and 40HZ) has been investigated. The catalysts were characterized by temperature programmed desorption, nitrogen adsorption–desorption, thermogravimetric analysis, Fourier transform infrared spectroscopy, X-ray diffraction, field-emission scanning electron microscopy and energy dispersive X-ray techniques. The large pore diameters (>19 nm) of the prepared catalysts alleviated the coke deposition effect. Also, the specific surface area and acidity of the samples surged from 18 to 22 m 2 /g and 0.38 to 1.24 mmol/g cat, respectively by varying HSiW loadings from 10 to 40 wt% on zirconia. The highest acrolein yield achieved was 63.75% at 92% glycerol conversion over 30HZ catalyst for 10 wt% glycerol feed concentration and 300 °C reaction temperature in 3 h. The combined physico-chemical characteristics of 30HZ made it more superior compared with other samples in the current study. [ABSTRACT FROM AUTHOR]

Xylose together with other pentose and hexose sugars can be dehydrated to produce interesting platform chemical compounds, like 5-hydroxyfurfural (HMF) and furfural. This study continues our investigation on the niobium oxide based catalysts in connection with the research of adequate solvents systems to minimize catalyst deactivation and increase catalyst stability and durability during the dehydration of sugars. Silica-zirconia supported niobia samples (10 wt.% of Nb) prepared by impregnation or sol–gel in comparison with pure niobic acid are here presented for xylose dehydration. The reactions have been studied at different temperatures (130–180 °C) in batch or fixed bed continuous catalytic reactors in various solvents. Green solvents soluble in the aqueous solution of xylose or biphasic systems have been taken into account: water, water–isopropanol mixtures, water-γ-valerolactone, and water-cyclopentylmethyl ether. The surface acidities of the catalysts have been measured in cyclohexane ( intrinsic acidity) and also in water to determine the effective catalyst acidity. The continuous tests and batch-recycling tests showed that the supported Nb-catalysts, even if initially less active, are more stable than niobic acid. The presence of isopropanol in water improves both the activity and stability of the catalysts in comparison with water and the use of cyclopentylmethyl ether gave the most interesting selectivity to furfural preserving the catalyst stability. [ABSTRACT FROM AUTHOR]

A series of solid acid catalysts based on vanadium and vanadium–phosphorous supported on a zirconium doped mesoporous SBA-15 silica has been synthesized, characterized by using XRD, N 2 sorption, NH 3 –TPD, FT-IR spectroscopy, X-ray photoelectron spectroscopy and diffuse reflectance UV–vis spectroscopy, and evaluated in the gas-phase dehydration of glycerol. Under the operating conditions used, all materials are active in the glycerol dehydration, being acrolein the main product in all cases. Although higher values of conversion are obtained in the presence of vanadium oxide based catalysts, acrolein yield improves after the treatment with phosphoric acid, attaining a value of 42% after 2 h of reaction at 325 °C with the 12VP0.2 catalyst, which contains 12 wt.% of V 2 O 5 and a V/P molar ratio of 0.2. However, the incorporation of phosphorous to the catalytic system partially destroys the mesoporous structure. Allyl alcohol has been also detected using vanadium based catalysts, due to a partial reduction of V 2 O 5 species during the reaction, increasing its yield with the vanadium oxide loading. All catalysts suffer from deactivation by coke deposition on the catalyst surface, being the carbon content considerably higher for catalysts without phosphorous. [ABSTRACT FROM AUTHOR]

A superhydrophobic mesoporous polymer-based acid catalyst (P-SO 3 H) was synthesized from solvothermal co-polymerization. The N 2 sorption isotherms indicate the rich porosity of P-SO 3 H, confirmed by the TEM image. The IR spectra indicate the presence of sulfonic acid groups. Interestingly, P-SO 3 H gives contact angle of water droplet on the sample surface at 154°, suggesting its superhydrophobicity. More importantly, P-SO 3 H is highly efficient catalyst for dehydration of sorbitol to isosorbide, giving sorbitol conversion higher than 99.0% and isosorbide yield at 87.9%. In addition, P-SO 3 H exhibits excellent recyclability. After recycles for 5 times, the isosorbide yield is still 77.7%. In contrast, conventional acid catalyst of Amberlyst-15 shows the yield at only 15.4% after recycles for 3 times. The unique catalytic properties are reasonably related to the superhydrophobicity and porosity of P-SO 3 H. The sample large porosity offers a high degree of the exposed acidic sites to the reactants, and the sample superhydrophobicity would keep the water formed in the dehydration away from the catalyst, promoting the reaction equilibrium. As a result, the catalytic performance in dehydration of sorbitol to isosorbide over the superhydrophobic P-SO 3 H catalyst is significantly enhanced, compared with conventional acid catalyst of Amberlyst-15. [ABSTRACT FROM AUTHOR]

Highlights: [•] Reactions of glycerol, 1,2- and 1,3-propanediol on various acid–base catalysts were compared. [•] Similarity between the dehydration reactions of 1,2-propanediol and glycerol were disclosed. [•] 1,3-Propanediol reacted quite differently from 1,2-propanediol, as well as glycerol. [•] Mechanistic consideration on the activation of propane polyols on acid–base catalysts is given. [Copyright &y& Elsevier]

Highlights: [•] A modified biphasic system was applied for producing furfural from xylose. [•] 3563.3μmol/g of furfural yield with 97.9% xylose conversion was obtained. [•] The optimum biphasic system (water:DMI/MIBK:2-butanol, 8:2/7:3) was obtained. [Copyright &y& Elsevier]

Highlights: [•] Comparison of the catalytic behavior of WO3 dispersed on Al2O3, ZrO2 and SiO2 is presented. [•] Effects of WO3 dispersion and supporting materials on the catalyst performance are uncovered. [•] Correlations between the catalytic behavior and WO x -density on support surfaces are given. [•] WO x -density and reaction temperature leading to maximum acrolein selectivity are identified. [Copyright &y& Elsevier]

Highlights: [•] Mesoporous niobium oxide is active in acid-catalyzed dehydration of xylose. [•] Xylose conversions higher than 70% were obtained after 45min at 140°C. [•] At 170°C and 90min, a maximum furfural yield of 50% was achieved. [•] No leaching of niobia was detected in the reaction medium. [ABSTRACT FROM AUTHOR]

Highlights: [•] Direct production of furan-based diols via one-pot cascade reactions was realized. [•] IL serves as an advantageous solvent in both hydrolysis and dehydration reactions. [•] Metal species and nature of the supports strongly affect products’ selectivity. [•] The controllable production of two kinds of furan-based diols was achieved. [Copyright &y& Elsevier]

Highlights: [•] 50HPW/Cs-SBA gave 85% of acrolein yield in glycerol dehydration. [•] Active sites are medium acid sites of HPW dispersed on Cs+ modified SBA-15. [•] Acrolein yield was correlated with fraction of medium acid sites. [•] Catalyst activity was completely recovered after coke burning regeneration. [Copyright &y& Elsevier]

Highlights: [•] We prepare PO4/Nb2O5 catalyst using the incipient impregnation method. [•] The amount of the acid sites and strength of the surface acidity increased with the amount of PO4 supported. [•] Conversion of glycerol and selectivity of acrolein are strengthened by increasing the PO4 content. [•] The catalyst could not be fully recovered because of the significant amount of PO4 loss during reaction. [ABSTRACT FROM AUTHOR]

Highlights: [•] MFI zeolites at various Si/Al ratios have been prepared and characterised. [•] Catalysts have been tested for methanol to DME dehydration reaction. [•] Conversion data have been obtained at different temperature. [•] Activation energy has been calculated as a function of the catalyst acidity. [•] The lower is the catalyst acidity, the lower activation energy. [Copyright &y& Elsevier]

Highlights: [•] Activity of ZrO2 and TiO2 based catalysts in the gas phase dehydration of glycerol. [•] Determination of surface acidity/basicity by FTIR of CO2 and pyridine. [•] Relationship of surface acid/base features with selectivity and conversion. [•] Influence of the nature of basic sites on the selectivity. [Copyright &y& Elsevier]