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Calcium pyrophosphate and hydroxyapatite catalysts with varying C/P ratios have been previously used by our group for vapor phase dehydration of lactic acid to acrylic acid with almost 100% conversion and up to 78% acrylic acid selectivity. The activity was highly sensitive to acidity and basicity of the catalyst. Hence the catalyst with maximum activity, calcium pyrophosphate, was modified with MoO3 for modifying its acidity and to study its effect on product selectivity for lactic acid dehydration. The MoO3 modified calcium pyrophosphate with 5% MoO3 loading was used for vapor phase dehydration of lactic acid at 375°C using 50% lactic acid concentration with WHSV of 3 h-1. The activity was compared with nonmodified calcium pyrophosphate catalyst. Surprisingly, deoxygenation was predominant compared to dehydration. Acidity was observed to play a crucial role in product selectivity (i.e,. with less acidic support, calcium pyrophosphate with 5 wt% MoO3 showed more deoxygenation activity as compared to acidic support γ-Al2O3 as well as SiO2 with same MoO3 loading). Higher acidity led to formation of acetaldehyde as the only product. The results confirmed formation of propionic acid by deoxygenation of lactic acid using in situ generated hydrogen after decarboxylation of lactic acid to acetaldehyde.

International audience; Palladium catalysts supported on acidic fluorinated magnesium hydroxide Pd/MgF2x(OH)x were prepared through precipitation or impregnation methods. Applications to the hydrogenation of various aldimines and ketimines resulted in good catalytic activities at mild temperatures using one atmosphere of hydrogen. Quinolines, pyridines and other Nheterocycles were successfully hydrogenated at higher temperature and hydrogen pressure using low palladium loadings and without the use of any acid additive. Such reactivity trend confirmed the positive effect of the Brønsted and Lewis acid sites from the fluorinated magnesium hydroxide support resulting in the effective pre-activation of N-heterocycle substrates and therefore in the good catalytic activity of the palladium nanoparticles during the hydrogenations. As demonstrated in the hydrogenation of imines, the catalyst was recycled up to 10 times without either loss of activity or palladium leaching.

WO3/SiO2 solid acid catalyst synthesized using sol gel method has shown promising activity (up to 65% conversion) for aromatic nitration in liquid phase using commercial nitric acid (70%) as nitrating agent without using any sulfuric acid. The water formed during the reaction as well as water from dilute nitric acid (70%) was removed azeotropically, however due to the hydrophilic nature of the catalyst, some water gets strongly adsorbed on catalyst surface forming a barrier layer between catalyst and organics. This prevents effective adsorption of substrate on catalyst surface for its subsequent reaction. To improve the activity further, the hydrophilic/hydrophobic nature of the catalyst was altered by post modification by grafting with commercial short chain organosilane (Dynasylan 9896). The modified 20% WO3/SiO2 catalyst when used for o-xylene nitration in liquid phase, showed significant increase in the conversion from 65% to 80% under identical reaction conditions. Catalyst characterization revealed decrease in the surface area of 20% WO3/SiO2 from 356 m2/g to 302 m2/g after grafting with Dynasylan 9896. The fine dispersion of WO3 particles (2–5 nm) on silica support was not affected due to modification. NMR and FTIR study revealed the decrease in surface hydroxyl groups imparting hydrophobicity to the catalyst. Interestingly the total acidic sites of the catalyst remained almost unaltered (0.54 mmol NH3/g) even after modification. Even though, the acidity and other characteristics of the catalyst did not change appreciably, there was a considerable increase in the o-xylene conversion which can be ascribed to the hydrophobic nature of the catalyst.

A single step synthetic procedure for carbon microspheres from agricultural waste residue (sugarcane bagasse) by low-temperature hydrothermal carbonization using oxalic acid as a hydrating/dehydrating agent is developed. The FTIR and XPS spectroscopy analysis indicates the presence of −OH, −COOH, and C═O functional groups on the surfaces of carbon spheres. These functional groups of the carbon spheres were utilized as a novel route to anchor 3-aminopropyl-triethoxysilane and 3-(2-aminoethylamino)propyl)-trimethoxysilane via condensation of triethoxy/trimethoxy silanes for the synthesis of organo base supported on carbon catalysts. The catalytic activity of the obtained supported organo-base catalyst was demonstrated for C–C bond forming (Henry) reaction. Among all prepared catalysts, 3-(2-aminoethylaminopropyl)-trimethoxysilane grafted in toluene showed high conversion (up to 100%) of aldehydes with excellent selectivity toward β-nitrostyrene. The catalyst was reused five times without losing significant ...

The synthesis of highly active and reusable mesoporous siliceous phosphotungstic acid materials (mPTA-Si) which are prepared through a simple self-assembly between phosphotungstic acid (PTA), the polymeric surfactant, and the silica precursor assisted by KCl for cyclohexylation of phenol is reported. The surface area and the acidity of these materials are tuned with a simple adjustment of PTA in the silica framework. The prepared samples exhibit mesoporous structure with a high surface area, but the structure is collapsed when the loading of PTA is high. It is established that the Keggin structure of PTA is retained on the final mPTA-Si. mPTA-Si with different loadings of PTA are employed as the catalysts for the cyclohexylation of phenol under liquid phase conditions. Among the catalysts studied, 10.0-mPTA-8.3Si calcined at 350 degrees C is found to be highly active, selective, and recyclable and offers 100% conversion of phenol with the highest selectivity for p-cyclohexylphenol (96.8%). Refereed/Peer-reviewed

Mesoporous tin oxide was prepared by template assisted and template-free methods. As-prepared materials were calcined at various temperatures to generate different nature (Bronsted and Lewis), amount and strength of acidic sites. The physico-chemical properties of the catalysts were studied by XRD, N2 sorption, pyridine-FTIR, NH3-TPD, DRS UV-vis, TGA, SEM, TEM, 1H MAS and 119Sn MAS NMR analyses. The catalytic behavior of mesoporous tin oxide catalysts was evaluated for acetalization and ketalization of glycerol with benzaldehyde and acetone respectively under solvent free conditions. The catalytic performance of mesoporous tin oxide was compared with that of other conventional solid acid catalysts namely H-ZSM-5, H-mordenite, H-beta, Al-MCM-41, Al-SBA-15 and Al-TUD-1. The efficiency of mesoporous tin oxide was also tested for cyclohexene epoxidation reaction. The catalyst prepared by template assisted method showed excellent catalytic performance compared to other catalysts due the difference in nature and amount of acidic sites in the catalyst. Meso-SnO2-T-350 was stable and reusable catalyst for four cycles without any appreciable loss in activity, and therefore it offers a good catalyst for potentially wide applications.

Selective oxidation of various alkanes/alkyl aromatics to corresponding carbonyl compounds has been carried out with very high conversion (∼98%) and selectivity (up to 100%) for carbonyl compounds using cyclopentadienyl molybdenum acetylide complex, CpMo(CO) 3 (C CPh) ( 1 ) as catalyst and tert -butyl hydrogen peroxide (TBHP) as an oxidant and turnover number (TON) of 88 was obtained with turnover frequency (TOF) of 2.45 h −1 . Mo acetylide oxo-peroxo species is formed in situ by reaction of 1 with TBHP during the course of reaction as catalytically active species. Interestingly even though the catalytically active species is homogeneous in nature it could be recycled very easily by recovering the catalytically active species as solid after addition of diethyl ether, and separating the products into organic phase. In the case of ethyl benzene oxidation, even after three recycles no appreciable loss in ethyl benzene conversion and acetophenone selectivity was observed. This complex showed high catalytic activity for the oxo functionalization of other alkyl aromatics and alkanes such as substituted ethyl benzenes, toluene as well as cyclohexane. TBHP was found to be more efficient oxidant than hydrogen peroxide for this oxidation.

A one-pot synthesis of molybdenum oxide nanoparticles (NPs) supported on bioderived carbon microspheres is reported. The catalyst was synthesized by the low temperature hydrothermal (LTH) method using d-glucose and bagasse as the carbon source. The carbonization of bagasse resulted in the formation of nonuniform carbon microspheres while glucose resulted in uniform carbon spheres. SEM and STEM elemental mapping show the uniform distribution of molybdenum oxide NPs over the carbon microspheres. XPS spectroscopy confirmed that molybdenum was in the Mo6+ oxidation state. The 1% MoO3 supported on carbon microspheres derived from d-glucose showed excellent catalytic activity up to 100% olefin conversion with 100% epoxide selectivity using organic tert-butyl hydroperoxide as an oxidant. The catalyst was successfully used for up to five cycles without losing substantial activity and selectivity.

The heterogeneously catalyzed esterification (acetylation) of glycerol toward triacetin in batch mode in presence of toluene as entrainer was studied. Silicotungstic acid, tungstophosphoric acid and phosphomolybdic acid as heteropolyacids (HPAs) supported on silica, alumina or silica-alumina were used as catalysts. The course of the reaction was found to be very sensitive to the nature of the HPA as well as the support. Solid characterization by Raman spectroscopy, XRD, and pyridine-FTIR revealed that only combinations of tungsten-based HPAs and silica support were able to preserve the structure of active component throughout the preparation process, which was essential to obtain active and selective catalysts. The interaction between HPA and support was decisive for stability and dispersion of the catalytically active species. With the best performing catalyst H 4 SiW 12 O 40 /SiO 2 , selectivity to triacetin reached 71% at complete conversion within 24 h. The high selectivity to triacetin is attributed the Bronsted acidic sites originated from stabilized Keggin structure and continuous removal of water during course of reaction. Toluene is able to form azeotropic mixtures with water and acetic acid and keeps the reaction temperature below the boiling point of acetic acid. Thus, water-free reaction conditions can be established. The catalyst was reusable; however, the activity and selectivity towards triacetin slightly decreased in a repetition run due to loss of active sites.

Palladium supported on a strontium hydroxyl fluoride catalyst was synthesized by a one-pot fluorolytic sol–gel method. The prepared catalyst was characterized by various physicochemical techniques. The sol–gel method has led to the formation of a high surface area (57 m2g−1), mesoporous (pore diameter = 13.0 nm) catalyst with uniform dispersion of Pd nanoparticles of size ∼7 nm on the surface of strontium hydroxyl fluoride. The catalyst was used for epoxide alcoholysis, and 100% conversion was obtained with 96% selectivity for β-alkoxy alcohols under mild conditions. The catalyst could be recycled for up to three catalytic cycles without any appreciable decrease in conversion and selectivity, indicating the stability of the catalyst under the reaction conditions. Further, the mechanism of alcoholysis was proposed on the basis of the physicochemical characteristics of the catalyst and on the basis of the products formed during the catalytic reaction.

High surface area mesoporous silica based catalysts have been prepared by a simple hydrolysis/sol–gel process without using any organic template and hydrothermal treatment. A controlled hydrolysis of ethyl silicate-40, an industrial bulk chemical, as a silica precursor, resulted in the formation of very high surface area (719 m 2 /g) mesoporous (pore size 67 A and pore volume 1.19 cc/g) silica. The formation of mesoporous silica has been correlated with the polymeric nature of the ethyl silicate-40 silica precursor which on hydrolysis and further condensation forms long chain silica species which hinders the formation of a close condensed structure thus creating larger pores resulting in the formation of high surface mesoporous silica. Ethyl silicate-40 was used further for preparing a solid acid catalyst by supporting molybdenum oxide nanoparticles on mesoporous silica by a simple hydrolysis sol–gel synthesis procedure. The catalysts showed very high acidity as determined by NH 3 -TPD with the presence of Lewis as well as Bronsted acidity. These catalysts showed very high catalytic activity for esterification; a typical acid catalyzed organic transformation of various mono- and di-carboxylic acids with a range of alcohols. The in situ formed silicomolybdic acid heteropoly-anion species during the catalytic reactions were found to be catalytically active species for these reactions. Ethyl silicate-40, an industrial bulk silica precursor, has shown a good potential for its use as a silica precursor for the preparation of mesoporous silica based heterogeneous catalysts on a larger scale at a lower cost.

A series of WO3/SiO2 catalysts have been prepared by sol-gel method using ammonium metatungstate and ethyl silicate-40 (ES-40) as WO3 and SiO2 precursors respectively. The sol-gel method has led to the formation of WO3 nano-particles of 2–5 nm well dispersed on mesoporous silica along with some WO3 agglomerates. Formation of monoclinic WO3 was seen on the catalysts above 5 wt% WO3 loading by XRD analysis. Silica has shown very high surface area of 606 m2/g which decreased gradually upto 368 m2/g with 20 wt% WO3 loading. 20 wt% WO3/SiO2 catalyst has shown maximum acidity (0.56 mmol NH3/g) with presence of both Lewis and Bronsted acidity. UV–vis DRS analysis showed formation of polytungstate species along with WO3 on silica surface. The prepared catalysts were used for liquid phase nitration of aromatics using 70% nitric acid as nitrating agent without using any sulfuric acid. Very high conversion (99%) was obtained for p-cresol nitration with very high selectivity (99%) for 2-nitro p-cresol. The water formed during the reaction was removed azeotropically using ethylene dichloride as solvent. In case of o-xylene 74% conversion was obtained with 54% selectivity for 4-nitro o-xylene. The effect of different WO3 precursors on nitration efficiency was studied using sodium tungstate and tungstic acid as precursors. However,ammonium metatungstate showed the highest acidity. Sodium tungstate showed formation of dimer of sodium tungstate which did not show any acidity and hence no activity for nitration. The mechanism for nitration using WO3/SiO2 has been proposed based on polarisation of water on tungsten centre generating Bronsted acidity which can further generate nitronium ion giving subsequently nitration of the aromatic ring.

International audience; This paper reports a short review on the impact of poisoning effects and thermal aging on the reactivity of surface vanadate species on benchmark V2O5−WO3/TiO2 Selective‐Catalytic‐Reduction catalysts. A renewed interest of this SCR technology is related to its diversification notably as after‐treatment systems to treat the exhaust from Diesel engines with higher running temperature especially when SCR catalysts are coated on Diesel Particulates Filters. Particular attention is also paid to poisoning effects in conjunction with the progressive replacement of fossil fuels by bio‐fuels containing alkaline contaminants which drastically deactivate the catalyst through neutralization of strong acid sites. Most of the investigations show that better insight into the mechanisms of poisoning and aging processes is needed especially to understand the relative sensibility of various vanadate species. This could provide original guidelines to catalyst preparation and or the developments of more stable bulk systems as exemplified.

Bimetallic Ag–Au/Al2O3 catalyst was synthesised by successive impregnation of 1% Au and 1% Ag on in-house prepared high surface area alumina (450 m2/g). The corresponding monometallic catalysts were also prepared by loading 1% Ag or 1% Au on the same high surface area alumina for comparison. The catalysts were characterised by various physico-chemical techniques and tested for SCR activity under lean burn engine exhaust conditions. Ag–Au/Al2O3 catalyst prepared by successive impregnation method showed considerably higher NO reduction (100%) to N2 compared to 1% Au/Al2O3 (70%) whereas the activity was comparable with that of 1% Ag/Al2O3 (96%). The effect of various pretreatments on SCR activity of Ag–Au/Al2O3 was studied and pretreatment at 250 °C in flow of hydrogen was found to give the best results with 100% NO conversion to N2 at 353 °C. Further ageing of the catalyst under reaction feed at 500 °C resulted in considerable increase in low temperature activity of bimetallic catalyst with ∼40% NO conversion at 222 °C. Even though the SCR activity of pretreated Ag–Au/Al2O3 and Ag/Al2O3 were comparable, after ageing the Ag–Au/Al2O3 showed significantly higher NO conversion (95%) compared to Ag/Al2O3 (83%) and Au/Al2O3 (70%). The formation of H2 and CO due to steam reforming of higher hydrocarbon (decane) was evidenced at the temperature of highest deNOx activity. Detailed investigation of the textural properties of the pretreated and aged catalysts showed presence of well dispersed metallic Au and Agnδ+ clusters after pretreatment in hydrogen at 250 °C.

International audience; This study emphasizes the importance of the preparation method for bimetallic Au–Ag catalysts supported on alumina in the selective reduction of NOx by hydrocarbons with gas feed compositions representative of diesel fuelled engine exhaust gas. An optimal balance between oxidative and reductive surface properties is obtained when Au and Ag are successively introduced. Significant re-dispersion processes take place when the catalyst runs at 500 °C leading to a gain in activity at low temperature and ascribed to a better interaction between Au and Ag species. Co-precipitation leads to a preferential formation of intermetallic Au–Ag particles which is detrimental to the catalytic performances. Aging at 500 °C leads to a significant particle sintering and a strengthening of the metallic character.

Uniformly sized silica microspheres were synthesized by a hydrolysis–condensation method. The obtained material was etched with a mild aqueous potassium hydroxide solution for different periods of time to break their Si–O–Si bonds and increases the density of hydroxyl groups on their surfaces. The resulting materials were then used as transition metal-free catalysts for oxidation of olefins in the presence of hydrogen peroxide as a green oxidant. The materials were thoroughly characterized using various physicochemical techniques. These highly populated hydroxyl groups on the surface of silica microspheres were proven to be responsible for excellent conversion (up to 93%) and epoxide selectivity (up to 100%) for various olefins. Quantum mechanical calculations also corroborate the experimental findings. Furthermore, both experimental and theoretical studies show that tertiary silanols were present at the active sites of the catalyst surface and were responsible for olefin epoxidation.

Esterification of glycerol with acetic acid in the presence of toluene as an entrainer was performed over acidic Amberlyst ion-exchange resins in a batch reactor. Toluene continuously removed the reaction water, thus the chemical equilibrium was effectively shifted; the selectivity for the most desired product triacetin was dramatically increased. The influence of reaction conditions such as reaction time, acetic acid: glycerol molar ratio and catalyst amount were investigated. More than 95% selectivity to triacetin at complete glycerol conversion was obtained. The ion-exchange resin catalysts were reusable in subsequent runs, but due to some deactivation the triacetin yields deteriorated.

A one-pot synthesis of palladium nanoparticles supported on magnesium hydroxide fluoride has been performed with the fluorolytic sol–gel method. The prepared catalysts were characterized by using various physicochemical techniques. The sol–gel method led to high surface area (>135 m2 g−1), mesoporous catalysts (pore volume=0.19–0.23 cm3 g−1, pore diameter=3–5 nm) with uniformly dispersed palladium nanoparticles approximately 2 nm in diameter on the surface. The catalysts synthesized by using different concentrations of aqueous hydrofluoric acid exhibited changing surface and acidic properties. Very high dispersion of palladium on magnesium fluoride (47 %) was obtained with 1 wt % palladium loading. The catalysts were used for hydrogenation of various olefins in the presence of other organic functionalities at room temperature and atmospheric hydrogen pressure. Various substituted olefins were hydrogenated with almost 100 % conversion and selectivity. The catalysts were recycled efficiently over five cycles without appreciable loss in catalytic activity. There was no palladium leaching under the reaction conditions, which was confirmed by inductively coupled plasma atomic emission spectroscopy analysis. Activation of olefin on the catalyst surface could not be observed by in situ FTIR studies, indicating facile activation of hydrogen on the palladium supported on magnesium hydroxide fluoride.

A series of magnesia doped Ag/Al 2 O 3 catalysts were prepared by modified impregnation method using boehmite as alumina precursor. The prepared catalysts were characterized and tested for the SCR of NO x using propene as reductant under lean condition. Doping of magnesia improved the low temperature catalytic activity for HC-SCR of NO x as well as sulfur tolerance. Maximum 98% NO conversion with 100% selectivity for N 2 was obtained at 350 °C with 7% Mg doping to Ag/Al 2 O 3 . The improvement in low temperature activity and the sulfur tolerance has been correlated to decreased acidity after addition of magnesia to alumina support. In situ FTIR study showed that the deactivation in the presence of SO 2 was due to the sulfation of silver and aluminum sites in Ag/Al 2 O 3 catalyst, however its formation was suppressed in case of magnesia doped Ag/Al 2 O 3 improving its sulfur tolerance.

Ultrasmall molybdenum oxide (MoO3) nanoparticles supported on various (SiO2, TiO2 or ZrO2) nanospheres were synthesized in one pot using a reverse micelle method. The prepared catalysts were thoroughly characterized by various physico-chemical methods. TEM images showed uniform dispersion of MoO3 nanoparticles (1.5–4 nm) onto silica (∼275 nm). No separate MoO3 particles were identified from TEM for MoO3/TiO2 (∼10.5 nm) and MoO3/ZrO2 (∼6.5 nm) because AHM reacted with titanium and zirconium hydroxides to form solid solution. Among the prepared catalysts MoO3/SiO2 showed excellent catalytic activity (up to 90% conversion and 100% epoxide selectivity) for olefin epoxidation. The catalyst was successfully recycled up to five cycles without losing much activity and selectivity.

Calcium phosphate catalysts were prepared by co-precipitation method using calcium nitrate and mixtures of ammonium and different sodium phosphates as calcium and phosphate precursors, respectively. Depending on the phosphate precursor, the pH of the synthesis mixture changed during the catalyst precipitation. The catalyst characterisation by XRD and ICP revealed the formation of a calcium pyrophosphate structure with varying Ca/P ratio from 1.02 to 0.76 which could be correlated to the different pH of the synthesis solutions. Vapour phase dehydration of lactic acid to acrylic acid was carried out using these calcium pyrophosphate catalysts. Non-stoichiometric calcium pyrophosphate catalyst with Ca/P ratio 0.76 was found to be the most efficient catalyst among the synthesized series with 100% lactic acid conversion and 78% acrylic acid selectivity at 375 °C. The higher selectivity for acrylic acid has been correlated to the increased acidity and reduced basicity of non-stoichiometric calcium pyrophosphate compared to other stoichiometric pyrophosphates. In situ FTIR studies showed the formation of a higher amount of calcium lactate on non-stoichiometric compared to stoichiometric pyrophosphate leading to higher selectivity for acrylic acid.

Pyruvates are important intermediates for various bioactive and pharmaceutical molecules. Synthesis of pyruvates is challenging due to low selectivity, as the pyruvates are prone to polymerisation. In the present work, oxidative dehydrogenation of ethyl lactate to ethyl pyruvate was carried out under very mild conditions using vanadium-based homogeneous and heterogeneous catalysts in the presence of aqueous t-butyl hydroperoxide as an oxidant. Homogenous vanadium-based catalyst, VO(acac)2 in acetonitrile solvent, gave excellent conversion (upto 83%) with 100% selectivity to ethyl pyruvate at room temperature. However, the heterogeneous catalyst, V2O5 exhibited very high activity for oxidative dehydrogenation of ethyl lactate only at higher temperature (80 °C). At higher temperature, significant TBHP decomposition was observed if all TBHP was added in one lot. In case of ethyl lactate dehydrogenation using V2O5 catalyst at 80 °C with two equivalents TBHP, 60% ethyl lactate conversion with 100% TBHP conversions were observed after 5 h when all TBHP was added initially in the reaction mixture. However, the ethyl lactate conversion at 80 °C, after 5 h increased to 72% when the same amount of TBHP was added batch wise over a period of 4 h, indicating improved conversion of TBHP to ethyl pyruvate. The heterogeneous catalyst, V2O5 exhibited up to 98% conversion with 100% ethyl pyruvate selectivity at 80 °C after 10 h with 3 equivalent TBHP added batch wise. The homogeneous catalyst could not be reused while V2O5 could be successfully recycled five times without catalytic performances loss. Oxidation proceeds by radical mechanism, as proved by experiment with radical scavenger.

Metal oxide supported mesoporous catalysts are receiving great attention nowadays because of their abilities to catalyze various key chemical reactions. A simple and cost-effective synthesis of thermally stable mesoporous solid acid catalysts is desired to replace conventional homogeneous catalysts for acid-catalyzed reactions to overcome the well-known drawbacks associated with homogeneous catalytic reactions. 3] One such largely studied mesoporous solid catalyst is MoO3 supported on various supports. Silica-supported molybdenum oxide (MoO3/SiO2) catalysts with varying MoO3 loading prepared by using different methods have been used for various organic transformations, such as olefin metathesis, selective oxidation, oxidative dehydrogenation of light alkanes, and photocatalytic oxidation of CO. MoO3/SiO2 has also been used extensively to catalyze the selective oxidations, such as methane to methanol. It also gives activity comparable to that of the commercial catalyst TS-1 for the liquid-phase epoxidation of propylene, which is an important industrial process commercialized by Sumitomo using TS-1 and cumene hydroperoxide as an oxidant. Much research work has been performed on the use of MoO3/SiO2 as a solid acid catalyst. For example, MoO3/SiO2 catalysts prepared by the sol–gel process were used for electrophilic aromatic nitration with N2O5. [13] Park et al. used MoO3/SiO2 prepared by using the wet impregnation technique for the isomerization of 2-butene to 1-butene. In our group, a series of mesoporous MoO3/SiO2 (1–20 mol% MoO3 loading) solid acid catalysts were synthesized using the simple sol–gel technique with ethyl silicate-40 as a novel silica source and ammonium heptamolybdate as a molybdenum source and with no surfactant/template and hydrothermal treatment. These MoO3/SiO2 catalysts were prepared and used for various acid-catalyzed organic transformations, such as nitration of benzene and cumene, transesterification, Beckmann rearrangement, acetalization of glycerol, and one-pot synthesis of 2,4,5-trisubstituted imidazoles. Among the series, 20 mol% MoO3/SiO2 has shown very high acidity and hence very high catalytic activity for many reactions. Although there are many reports that describe the synthesis of MoO3/SiO2 catalysts by using various techniques and their catalytic activity for various oxidation and acid-catalyzed reactions, so far there are no reports that describe the nature of catalytically active species formed on MoO3/SiO2 in various organic transformations. Hence, to study the nature of catalytically active species formed during acid-catalyzed reactions with the MoO3/SiO2 catalyst prepared by the sol–gel process, the esterification of ethWe report the isolation, characterization, and identification of the catalytically active species formed during various acid-catalyzed reactions if silica-supported MoO3 was used as a catalyst. We have reported previously the synthesis and extensive characterization of the silica-supported MoO3 catalyst prepared by the sol–gel process with ammonium heptamolybdate and ethyl silicate-40 as molybdenum and silica precursors, respectively. The TEM images showed uniformly distributed MoO3 nanoparticles on the high-surface area mesoporous silica support and high acidity (0.9 mmolg ) by using temperature-programmed desorption of ammonia (NH3-TPD) analysis. This catalyst has already shown high activity for various acid-catalyzed reactions. To understand the nature of catalytically active species formed during the reaction, the liquid-phase esterification of acetic acid and ethanol was studied as a probe reaction with very high acid conversion (83%) in 8 h. During esterification, the reaction mixture turned blue, which indicated a change in the nature of the catalyst under reaction conditions. These catalytically active species formed in the reaction mixture were isolated and extensively characterized by using FTIR, Raman, powder XRD, BET surface area, NH3-TPD, energy dispersive X-ray, and TEM analysis. The characterization results revealed the in situ formation of silicomolybdic acid on the silica surface in the presence of water, which acts as catalytically active species responsible for the acid-catalyzed reactions.

Titania-based hydrodesulfurization catalysts were prepared by using a one-pot sol–gel method with the titanium peroxo complex as titanium precursor and molybdenum and cobalt precursors dissolved in the aqueous hydrogen peroxide solution used during synthesis. Catalysts with MoO3 loadings varying from 5 to 40 wt % and a Co/Mo atomic ratio of 0.5 were prepared. Solids with molybdenum loadings below 20 wt % MoO3 demonstrated poor hydrodesulfurization activity for the model compound thiophene. This was attributed to the presence of a large amount of embedded cobalt and molybdenum species in the titania matrix. A significant increase in the catalytic activity was observed for solids containing 20 and 25 wt % of MoO3 on which active species appeared to be accessible on the titania surface. Furthermore, the highest conversion obtained on these sol–gel solids was superior to the highest conversion obtained on reference catalysts prepared through the impregnation of ammonium heptamolybdate and cobalt nitrate on commercial titania.

The synthesis and catalytic properties of molybdenum acetylide complexes CpMo(CO)3(–C≡CR), R = Ph(1), C6H4–p-CF3 (2) and C6H4–p-CH3 (3) has been studied. The molybdenum acetylide complexes were synthesized from CpMo(CO)3Cl and aryl acetylenes via Stephens–Castro coupling reaction. These complexes were characterized by single crystal X-ray diffraction analysis, FTIR and 1H NMR spectroscopy. These complexes on treatment with hydrogen peroxide, formed corresponding molybdenum oxo-peroxo species. These in situ formed oxo-peroxo species were found very active (up to 100 % conversion) and selective (up to 100 %) oxidation catalysts for various refractory and nonrefractory sulfides. Interestingly, even though the molybdenum acetylide complexes are homogeneous, they could be recycled very efficiently by extracting the catalytically active molybdenum oxo-peroxo species in aqueous phase. Molybdenum acetylide complexes CpMo(CO)3(C≡CR) synthesized from CpMo(CO)3Cl via Stephens- Castro coupling with aryl acetylenes were used as catalyst precursors for selective oxidation of various sulfides including refractory sulfides to sulfoxides or sulfones using H2O2 as an environmentally benign oxidant with excellent conversion under mild reaction conditions.

Catalytic properties of supported gold catalysts on γ -Al 2 O 3 prepared by a conventional deposition–precipitation method were compared with those obtained by anionic‐exchange for the reduction of NO x by hydrocarbon under lean conditions that simulate Diesel engine exhaust gas. Interestingly, a catalytic activity enhancement is observed after thermal ageing under reactive conditions at 500 °C on anionic-exchanged samples which make them suitable for practical developments. On the other hand, the reverse trend is observed on the solids prepared by deposition–precipitation which deactivate at low temperature. Such changes in catalytic properties have been tentatively explained on the basis of textural and structural modifications taking place during thermal ageing under wet atmosphere.

A simple one-pot synthesis has been developed for the synthesis of 2,4,5-trisubstituted imidazoles using an efficient and recyclable MoO3/SiO2 solid acid catalyst by condensation of benzil or benzoin, benzaldehyde, and ammonium acetate in acetonitrile as a solvent. Using this solid catalyst, the reactions could be carried out under mild reaction conditions with very good yield of imidazoles, up to 95%. This catalyst could be recycled very easily, which makes this methodology environmentally benign.

Gold supported on alumina was prepared by urea deposition-precipitation method and compared to silver supported on alumina for the selective catalytic reduction of NO by hydrocarbons under lean conditions. The catalyst showed activity in the reduction of NO and 100% selectivity towards N2 in the temperature range 300–350 °C. At higher temperature the NO conversion decreased due to competitive oxidative reactions of the reductants. XPS analysis confirmed the good stability of gold nanoparticles deposited on alumina. Infrared studies showed the formation of various adsorbed species (formates, carboxylates, ad-NOx and cyanide) on the catalyst surface. Addition of H2 to the feed containing decane enhanced the formation of these species on the catalyst surface as well as the catalytic activity for the NO conversion to N2.

Thin films of vanadia–titania with good adhesion to the substrates have been deposited on various substrates such as glass slides, glass helix and silica raschig rings by simple sol–gel dip coating process using vanadium and titanium peroxide gel. The optimum concentration of vanadia in titania for obtaining good uniform viscous gel was found to be 0.5–4 wt% beyond which the vanadia particles disturb the gel network, resulting in the formation of a gelatinous precipitate. The films of vanadia–titania as well as the dried powder of the bulk gel were characterized by different characterization techniques. Optical characterization by UV–vis spectrophotometer showed a shift in optical absorption wavelength to the visible region that may be due to the incorporation of vanadia into titania structure. The XRD revealed the formation of anatase phase in pure titania as well as titania with up to 2% vanadia loading, whereas formation of rutile as minor phase along with anatase as major phase was observed at higher vanadia loading. The XRD did not show any peaks of vanadia phase up to 5% vanadia loading indicating either incorporation of vanadia into titania structure or high dispersion of amorphous vanadia on titania support. The pure and vanadia doped TiO2 thin films were evaluated for their photocatalytic activity for degradation of methylene blue as a model pollutant under sunlight. Doping of V2O5 in TiO2 showed an increase in the photo-degradation rate of methylene blue by a factor of 3–6.6 times compared to pure TiO2. The highest rate has been obtained for 4% V2O5-doped TiO2 films. Vanadia doped TiO2 thin films were also found to be very active for photocatalytic degradation of formaldehyde from aqueous solution in sunlight.

Acetalization of glycerol with various aldehydes has been carried out using mesoporous MoO3/SiO2 as a solid acid catalyst. A series of MoO3/SiO2 catalysts with varying MoO3 loadings (1–20 mol%) were prepared by sol–gel technique using ethyl silicate-40 and ammonium heptamolybdate as silica and molybdenum source respectively. The sol–gel derived samples were calcined at 500 °C and characterized using various physicochemical characterization techniques. The XRD of the calcined samples showed the formation of amorphous phase up to 10 mol% MoO3 loading and at higher loading of crystalline α-MoO3 on amorphous silica support. TEM analyses of the materials showed the uniform distribution of MoO3 nanoparticles on amorphous silica support. Raman spectroscopy showed the formation of silicomolybdic acid at low Mo loading and a mixture of α-MoO3 and polymolybdate species at high Mo loadings. Moreover the Raman spectra of intermediate loading samples also suggest the presence of β-MoO3. Acetalization of glycerol with benzaldehyde was carried out using series of MoO3/SiO2 catalysts with varying MoO3 loadings (1–20 mol%). Among the series, MoO3/SiO2 with 20 mol% MoO3 loadings was found to be the most active catalyst in acetalization under mild conditions. Maximum conversion of benzaldehyde (72%) was obtained in 8 h at 100 °C with 60% selectivity for the six-membered acetal using 20% MoO3/SiO2. Interestingly with substituted benzaldehydes under same reaction conditions the conversion of aldehydes decreased with increase in selectivity for six-membered acetals. These results indicate the potential of this catalyst for the acetalization of glycerol for an environmentally benign process.

Ag/Al 2 O 3 catalysts with 1 wt% SiO 2 or TiO 2 doping in alumina support have been prepared by wet impregnation method and tested for sulphur tolerance during the selective catalytic reduction (SCR) of NO x using propene under lean conditions. Ag/Al 2 O 3 showed 44% NO x conversion at 623 K, which was drastically reduced to 21% when exposed to 20 ppm SO 2 . When Al 2 O 3 support in Ag/Al 2 O 3 was doped with 1 wt% SiO 2 or TiO 2 the NO x conversion remained constant in presence of SO 2 showing the improved sulphur tolerance of these catalysts. Subsequent water addition does not induce significant deactivation. On the contrary, a slight promotional effect on the activity of NO conversion to nitrogen is observed after Si and Ti incorporation. FTIR study showed the sulphation of silver and aluminum sites of Ag/Al 2 O 3 catalysts resulting in the decrease in the formation of reactive intermediate species such as –NCO, which in turn decreases NO x conversion to N 2 . In the case of Ag/Al 2 O 3 doped with SiO 2 or TiO 2 , formation of silver sulphate and aluminum sulphate was drastically reduced, which was evident in FTIR resulting in remarkable improvement in the sulphur tolerance of Ag/Al 2 O 3 catalyst. These catalysts before and after the reaction have been characterized with various techniques (XRD, BET surface area, transmittance FTIR and pyridine adsorption) for physico-chemical properties.

A facile method for the synthesis of porous platinum nanoparticles by transmetallation reactions between sacrificial nickel nanoparticles and chloroplatinic acid (H(2)PtCl(6)) in solution, as well as at the constrained environment of the air-water interface, using a Langmuir-Blodgett instrumental setup is presented. To carry out the transmetallation at the air-water interface hydrophobized nickel nanoparticles are assembled as a monolayer on the sub phase containing platinum ions. The porous Pt nanoparticles obtained as a result of the reaction are found to act as extremely good catalysts for hydrogenation reaction. The products are well characterized by TEM, HRTEM, EDAX, and STEM. Attempts are made to postulate the plausible mechanism of this reaction to generate this kind of nanoparticle with controllable geometric shape and structure. This simple strategy has the potential to synthesize other nanomaterials of interest too.

Selective oxidation of various aromatic alcohols to aldehydes has been carried out with very high conversion (90%) and selectivity (90%) for aldehydes using cyclopentadienyl molybdenum acetylide complex, CpMo(CO)3(CCPh) (1) as catalyst and hydrogen peroxide as environmentally benign oxidant. Water-soluble Mo acetylide oxo-peroxo species is formed in situ after reaction of 1 with aqueous hydrogen peroxide during the course of reaction as catalytically active species. Interestingly even though the catalyst is homogeneous it could be recycled very easily by separating the products in organic phase and catalyst in aqueous phase using separating funnel. Even after five recycles no appreciable loss in alcohol conversion and aldehyde selectivity was observed.

The molybdenum acetylide oxo-peroxo complex obtained in situ by the treatment of the corresponding molybdenum acetylide carbonyl complex, CpMo(CO)3(C CPh); Cp = η5-C5H5 with H2O2, has been used as an efficient catalyst for selective N-oxidation of primary amines to nitroso derivatives. Excellent amine conversion (up to 100%) and very high selectivity for nitroso compounds (99%) have been obtained using 30% hydrogen peroxide as an oxidant. The oxo peroxo Mo(VI) complex has also been found to be very active for the oxidation of various substituted primary aromatic amines with electron donating as well as electron withdrawing substituents on the aromatic ring.

Selective cis -dihydroxylation of various olefins has been carried out using molybdenum acetylide complex CpMo(CO) 3 (C CPh) ( 1 ) as catalyst and hydrogen peroxide as an efficient and environmentally benign oxidant. In case of cyclohexene, very high conversion (95%) and selectivity (86%) for cis -dihydroxylated product has been achieved using H 2 O 2 as an oxidant and t -butanol as a solvent. cis -Dihydroxylation of other substrates like styrene, α-methyl styrene, limonene and cyclopentene has also been carried out with very high selectivity for diol. The catalyst and intermediate species have been characterized using FT-IR, UV–vis spectral analysis and XPS studies as well as cyclic voltametric studies. These studies suggest that molybdenum oxo–peroxo complex is the catalytically active species. The intermediate blue complex when characterized by ESI MS suggested the formation of dimeric molybdenum complex and XPS and cyclic voltametric studies confirm the presence of mixed valence Mo(V) and Mo(VI) in the reaction intermediate. Based on the characterization results possible mechanism for dihydroxylation is proposed. Interestingly, even though the catalyst is homogeneous; it could be recovered quantitatively by extraction in aqueous phase and recycled five times without any appreciable loss in cyclohexene conversion and selectivity for cis -1,2-cyclohexanediol.

Antimicrobial drug, tinidazole has been synthesized by condensation of 2-methyl,5-nitro-imidazole and 2-ethyl-thio-ethanol over MoO 3 /SiO 2 catalyst to obtain 1-(2-ethyl-thio-ethanol)-2-methyl-5-nitro-imidazole which is further oxidized using hydrogen peroxide using the same MoO 3 /SiO 2 catalyst to obtain tinidazole. MoO 3 /SiO 2 catalyst (20%), synthesized by sol–gel process showed the highest acid strength and was successfully demonstrated to catalyze both condensation and oxidation in the synthesis of tinidazole. Due to the bifunctional activity of the catalyst, the use of acetic acid for condensation step and tungstic acid or ammonium molybdate for oxidation step in the conventional synthesis of tinidazole could be eliminated, thus making it an environmentally benign process. The catalysts could be recycled five times without any appreciable loss in the conversion and selectivity showing the potential for the use of MoO 3 /SiO 2 as bifunctional catalyst for the production of this industrially important compound.

Barium oxide containing catalysts with different compositional and structural features have been prepared by impregnation and sol–gel technique for NO x storage reduction (NSR). Barium oxide supported on γ -alumina prepared by impregnation method exhibited better NO x storage reduction behavior compared to the catalysts prepared by sol–gel process. Barium oxide containing ceria/zirconia catalysts were also prepared without alumina, which showed lower NO x storage compared to alumina supported catalysts. In this case also the catalysts prepared by impregnation displayed better NO x storage behavior than the catalyst prepared by sol–gel process. The catalysts were characterized by X-ray diffraction analysis and BET surface area measurements. XRD and BET surface area measurements indicated the influence of structure and composition of the support on the NO x storage behavior of barium oxide.

Inexpensive NiXMg2AlOY nanocomposites with high Ni content (Ni wt% > 40%) are developed as efficient catalysts for the sustainable hydrogen production from a mixture of ethanol and water at low temperature. The NiXMg2AlOY nanocomposites are composed of small and uniform nanoparticles (4–6 nm) of NiO, Ni–Mg–(Al)–O and/or MgO. The strong interactions existing between Ni2+ cations and Mg2+ and/or Al3+ cations either in the Ni–Mg–(Al)–O solid solution and/or at the interface of nanoparticles of NiO and/or Ni–Mg–(Al)−O make the catalyst highly active and stable. The behavior of the solids is analyzed in the presence of low and high concentrations of ethanol while maintaining a H2O/EtOH molar ratio of 3. The NiXMg2AlOY catalysts are shown to be efficient toward H2 production between 250 and 650 °C. In the presence of low concentration of ethanol, on the highly loaded Ni compound (Ni12Mg2AlOY), total conversion of ethanol is obtained at 250 °C without formation of CO and carbon, and at 300 °C a H2 yield of 3 mol molEtOH−1 is obtained without the formation of CO, exhibiting a remarkable stability with the time on stream even if some carbon is formed. In high concentration of ethanol, total conversion of ethanol is obtained at 450 °C on the highly loaded Ni compound (Ni12Mg2AlOY). In such conditions, a stable co-generation of carbon nanofibrous materials which amount increases with Ni content is also obtained. The catalytic stability is related to the type and morphology of the carbon species formed. The correlations among the catalyst properties, the catalytic performances and the characterizations are thoroughly discussed.

A newly synthesized molybdenum(VI) dioxo complex is used as a catalyst for the epoxidation of allylic alcohols and olefins.

Present work deals with the extended applicability of the in situ generated supported silicomolybdic heteropolyanions from the sol-gel synthesized MoO3/SiO2 catalyst for the acetylation of glycerol. The best results were obtained at 118°C using a glycerol: AcOH molar ratio of 1:10 with 100% glycerol conversion in 2 hr and 76% selectivity for triacetin when the reaction was continued for 20 hr.

The regioselective nitration of cumene to 4-nitro cumene (4-NC) has been carried out using 70% nitric acid over MoO 3 /SiO 2 solid acid catalyst with high conversion (62%) and selectivity (68%) for 4-NC. A series of MoO 3 /SiO 2 catalysts with different MoO 3 loadings (1–20 mol%) were prepared by sol–gel technique and characterized using different characterization techniques. XRD analysis revealed the amorphous nature of the catalyst up to 10-mol% MoO 3 loading and formation of α-MoO 3 crystalline phase on amorphous high surface area mesoporous silica support at higher MoO 3 loading. Maximum conversion and selectivity has been obtained with slower addition of nitric acid and simultaneous azeotropic removal of water formed during the reaction.