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Addition of gold to the Pt–CsPW catalyst has an enhancing effect on the HDO of DMTHF, with a twofold increase of turnover rate at Pt sites.

Acidic cesium salt of tungstophosphoric heteropoly acid, Cs2.5H0.5PW12O40 (CsPW), is an excellent solid acid catalyst for the reaction of phenylacetaldehyde with biorenewable monoterpenic alkenes: limonene, α-terpineol, α-pinene and β-pinene. Simultaneously with a conventional oxonium-ene cyclization to give an oxabicyclo[3.3.1]nonene compound, phenylacetaldehyde undergoes Friedel-Crafts alkylation by the monoterpenes resulting in a new product with an unusual fused tetracyclic structure, obtained in ca. 80 % yield. A combined yield for both products was up to 95 %. Styrene oxide can be also used as a starting material for these reactions to give the same products in up to 85 % combined yield. A novel one-pot tandem process thus developed involves the isomerization of styrene oxide into phenylacetaldehyde and cycloaddition of the latter to the monoterpene, with both steps being catalyzed by CsPW. The reactions were performed in green solvents diethylcarbonate or anisole, which have high sustainability ranks in modern solvent selection guides, comparable to those of ethanol and water.

2,5-Dimethylfuran is deoxygenated to n-hexane with 100% yield on a bifunctional Pt/C-Cs2.5H0.5PW12O40 catalyst under very mild conditions (90 °C, 1 bar H2) in a one-step gas-phase process. A proposed mechanism includes a sequence of hydrogenolysis, hydrogenation and dehydration steps occurring on Pt and proton sites of the bifunctional catalyst.

The role of 3D alumina foam support (Al-F) and titania-modified alumina foam support (Al-F-Ti-X, where X represents the weight ratio of Al-F/TiO2) on the dispersion and catalytic activity of NiMo m...

2,5-Dimethyltetrahydrofuran (DMTHF) is deoxygenated to

For ultra-deep desulfurization of diesel fuel, this study applied the ultrasound-assisted catalytic ozonation process to the dibenzothiophene (DBT) removal process with four Keggin-type heteropolyacids (HPA) as catalysts and acetonitrile as extractant. Through experimental evaluations, H3PMo12O40 was found to be the most effective catalyst for the oxidative removal of DBT. Under favorable operating conditions with a temperature of 0 °C, H3PMo12O40 dosage of 2.5 wt.% of n-octane, and ultrasonic irradiation, DBT can be effectively removed from simulated diesel. Moreover, the reused catalyst exhibited good catalytic activity in recovery experiments. This desulfurization process has high potential for ultra-deep desulfurization of diesel.

Keggin-type heteropoly acids supported on activated carbon (HPA/C) are active catalysts for oxidative desulfurization (ODS) of diesel fuel under mild conditions in a biphasic system composed of a benzothiophene-containing model diesel fuel (heptane) and aqueous 30% H2O2. The catalytic activity of HPA/C was found to decrease in the order of HPA: H3PMo12O40 > H3PW12O40 > H4SiW12O40. The most active catalyst, H3PMo12O40/C, exhibited 100% removal of benzothiophenes from model diesel fuel at 60 °C, and could be recovered and reused without loss of activity. This catalyst outperforms other recently reported heterogeneous catalysts for ODS in similar systems. Kinetic and DRIFTS studies provide new insights into the mechanism of ODS reaction on carbon-supported HPAs.

The aliphatic alcohols (methanol, ethanol, 1- and 2-propanol) were used for the upgrading of petroleum asphaltenes. The process was performed under supercritical (sc) conditions at 350 °C. CHNSO analysis and GC methods were used to characterize the elemental and chemical composition of the products preliminarily divided into three fractions: hexane-soluble (HSF), benzene-soluble (BSF), and insoluble residue (IR). It was shown that the sc alcohols leads to the decrease of total content of sulfur and nitrogen in the products (HSF + BSF + IR) by 18–23 and 31–33 wt%, correspondingly, as compared with the initial asphaltenes (IA). The highest yield of the soluble fractions (HSF and BSF) was observed for 1-propanol and ethanol. It appeared that the alcohols used as a reaction media are partially consumed by incorporating in the product molecules as alkoxy substituents. The H and O content of HSF and BSF for all alcohols was significantly higher than that for IA. The composition of hexane-soluble fraction obtained after sc upgrading is quite similar to chemical composition of the diesel fraction, specifically to straight-run gas oil. The efficiency of each supercritical alcohol used for the upgrading of asphaltenes is analyzed and discussed.

2,5-Dimethylfuran is deoxygenated to n-hexane with 100% yield on a bifunctional Pt/C-Cs

The isomerization of caryophyllene oxide, one of the most widespread sesquiterpenes found in various essential oils, is catalyzed by the acidic Cs salt of tungstophosphoric heteropoly acid, Cs2.5H0.5PW12O40, to give rare polycyclic oxygenated sesquiterpenes with a clovane structure. Cloven-9-ol and clovan-2,9-diol can be obtained with up to 80% combined selectivity and 60% individual selectivity each (under different reaction conditions), which is the best result reported for these compounds so far. The process is environmentally benign and can be performed not only in conventional solvents such as 1,2-dichloroethane and acetone but also in eco-friendly “green” organic solvents such as dimethylcarbonate, diethylcarbonate and 2-methyltetrahydrofuran. The reactions occur under ambient conditions at low catalyst loadings without catalyst leaching. The solid catalyst can be simply centrifuged from the reaction mixture, and low boiling solvents can be separated from reaction products by distillation.

Keggin-type polyoxometalates (POM) immobilized on alkylaminophosphazene (RPN)-functionalized silica (POM/RPN-SiO2) are new effective single-site solid catalysts for oxidative desulfurization (ODS) of diesel fuel under mild conditions in a biphasic system composed of a benzothiophene-containing model diesel fuel (heptane) and aqueous 30% H2O2. The catalytic activity of POM/RPN-SiO2 was found to be influenced by the choice of POM and the amine R group in RPN, decreasing in the order PMo > PW > SiW and Bz > iBu > iPr, respectively. The most effective catalyst, PMo/BzPN-SiO2 (PMo = PMo12O403−), exhibited 100% removal of dibenzothiophene from model diesel fuel at 60 °C and ambient pressure and could be reused without loss of activity. This catalyst outperforms other recently reported heterogeneous catalysts for ODS in similar systems. 13C, 29Si and 31P MAS NMR, FTIR, SEM, BET and elemental analysis were used to characterize the structure of surface phosphazene and POM species in the new catalysts.

Ketonisation of acetic acid to acetone was studied in the gas phase using γ-Al2O3, TiO2, ZrO2 and CeO2 as the catalysts in the temperature range of 180–350 °C and ambient pressure. Catalyst activity was found to increase in the order Al2O3

An original method for direct synthesis of tetramethyl orthosilicate from SiO2 raw minerals and supercritical methanol was developed for the first time in a flow mode. The process promoted by KOH was performed at 270 °C and 100 atm using 3 A zeolite molecular sieves to shift the reversible reaction toward TMOS formation by removing released water. The equilibrium constant Keq of the reaction was determined as 0.839E-08. Silica gel (100 wt% SiO2), quartz sand (97 wt% SiO2), expanded perlite (73 wt% SiO2) and vermiculite (38 wt% SiO2) were tested as SiO2 minerals. The highest equilibrium concentration of TMOS equal to 20.4 g/L was achieved for silica gel that can be increased using larger amount of water adsorbent.

The aliphatic alcohols (methanol, ethanol, and 1- and 2-propanols) were used for the first time as a reaction media for the upgrading of crude oil asphaltenes. The process was realized in a batch reactor under supercritical conditions (at 350 °C). The three main fractions of the products (hexane- and benzene-soluble fractions, HSF and BSF, and insoluble residue, IR) were analyzed using attenuated total reflection Fourier tranform infrared (ATR-FTIR) and 1H and 13C nuclear magnetic resonance (NMR) spectroscopy to characterize structural changes of the initial asphaltenes (IA). According to NMR data, the aliphatics are the main part of the hexane-soluble fraction (HSF) and benzene-soluble fraction (BSF). The alcohols were appeared to influence the content of both aliphatics and aromatics in the products. The content of aliphatics in the HSF increases in the line from “lighter” to “heavier” alcohols used but reduces in the BSF. However, the content of aromatics in the HSF increases from “heavier” to “lighter...

Acidic Cs salt of tungstophosphoric heteropoly acid, Cs2.5H0.5PW12O40 (CsPW), is excellent solid acid catalyst for liquid-phase cycloaddition reactions of biomass-based and easily available from essential oils monoterpenic compounds, such as limonene, α-terpineol, α-pinene, β-pinene and nerol, with aldehydes, including benzaldehyde, crotonaldehyde as well as biomass-derived cuminaldehyde and trans-cinnamaldehyde. The reactions give oxabicyclo[3.3.1]nonene compounds potentially useful for the fragrance and pharmaceutical industries in good to excellent yields. The process is environmentally benign and can be performed in biomass-derived solvent 2-methyltetrahydrofuran and eco-friendly “green” organic solvents such as dimethylcarbonate and diethylcarbonate under mild conditions at low catalyst loadings without leaching problems. The solid CsPW catalyst can be easily separated from the reaction media and low-boiling solvents can be removed by distillation. Silica-supported H3PW12O40 also demonstrated good performance in these reactions.

Silica-supported zinc oxide possessing acid and dehydrogenation functions is an efficient, noble-metal-free bifunctional catalyst for the environment-friendly synthesis of p-Cymene from renewable monoterpene feedstock by gas-phase dehydroisomerisation of α-pinene and limonene in a fixed-bed reactor. The reaction involves acid-catalysed terpene isomerisation to p-menthadienes followed by dehydrogenation to form p-Cymene. Dehydroisomerisation of α-pinene produces p-Cymene with 90% yield at 100% conversion at 370 °C and WHSV = 0.01–0.020 h−1. The reaction with limonene gives a 100% p-Cymene yield at 325 °C and WHSV = 0.080 h−1. ZnO/SiO2 catalyst shows stable performance for over 70 h without co-feeding hydrogen.

Keggin-type heteropoly acids (HPAs) H3PMo12O40 and H3PW12O40 supported on activated carbon were shown to be highly active catalysts for oxidative desulfurization (ODS) of model diesel fuel containing dibenzothiophene (DBT) and heptane by 30% H2O2. A number of commercial activated carbons differing in their acid-base properties were tested as the HPA support to reveal a strong effect of basicity of carbon support on the integrity of HPA structure on the carbon surface and catalyst activity. The most active catalysts, comprising decomposed H3PW12O40, outperformed best reported heterogeneous catalysts for ODS in similar systems, exhibiting 100% DBT removal from the model diesel fuel at 40–60 °C and H2O2/DBT = 3 mol/mol in 20–30 min with 85–88% H2O2 efficiency and could be recovered and reused without loss of activity. DRIFTS studies provided an insight into the mechanism of ODS reaction on carbon-supported HPAs.

Hydrodeoxygenation (HDO) of 2,5-dimethyltetrahydrofuran (DMTHF) was studied at a gas-solid interface in a fixed-bed microreactor in the presence of bifunctional metal-acid catalysts comprising Pt/C and acidic heteropoly salt Cs2.5H0.5PW12O40 (CsPW). The Pt–CsPW catalyst deoxygenated DMTHF to n-hexane with >99% selectivity under mild conditions (90–100 °C, ambient pressure) and was much more efficient than monofunctional Pt/C. On the basis of kinetic studies, a mechanism for the HDO of DMTHF over Pt–CsPW was proposed, which includes a sequence of hydrogenolysis, dehydration and hydrogenation steps catalysed by Pt and proton sites of the bifunctional catalyst. The turnover rate of HDO increased with increasing Pt particle size suggesting that the hydrogenolysis of C–O bond in furanic compounds on Pt is a structure-sensitive reaction.

The impact of CaO on oakwood pyrolysis was explored by the Py-GC/MS at 500 °C. Ca(OH)2 presents on the CaO surface, indicating its partial hydration (noted as CaOOH). CaOOH promoted the ketonisation of carboxylic acids to aliphatic ketones, furfural to cyclopentanone/2-cyclopentenone, facilitated the elimination of the methoxy-phenolic compounds. The catalyst loading did not show any significant effect on the formation of acetone, while a noticeable reduction in the phenolics was revealed. Increasing catalyst loading almost eliminated CO2, acids, furans, aldehydes, ether groups, whilst the fractions of alcohols, esters, sugars, and alkoxybenzene decreased noticeably. The use of partially hydrated CaOOH in the CFP can create conditions where by-products generated during the ketonisation and phenolics upgrading reactions (CO2, H2O, CO) interact through the adsorption enhance water-gas-shift reaction and through coking reactions with formation of H2 used for hydrogenation during multistep conversion of furfural to cyclopentanone in a vapour phase.

The reactions of biomass-based substrates, i.e., limonene, α-pinene, β-pinene, terpinolene, α-terpineol, nerol and linalool, with benzaldehyde in the presence of tungstophosphoric heteropoly acid H 3 PW 12 O 40 (HPW) supported on silica give an oxabicyclo[3.3.1]nonene compound with fragrance characteristics in good to excellent yields. The reactions apparently involve the formation of α-terpenyl carbenium ion by the protonation of alkene or dehydration of alcohol followed by the nucleophilic attack of benzaldehyde. The subsequent oxonium-ene cyclization of the resulting oxocarbenium ion gives the oxabicyclic product. The process is an environmentally benign and heterogeneous and can be performed under mild conditions with low catalyst amounts and no significant leaching of active components.

The sulfidation of NiMo catalyst by thermal decomposition of support surface-bound thiols to generate stoichiometric amount of H2S has proved to be a clean and remarkable approach for catalyst activation. The role of loading of thiol groups on the formation and dispersion of MoS2 active phase on the mesoporous silica support was further evaluated. The catalytic activity of the supported catalysts and a reference catalyst was evaluated in the hydrodesulfurization (HDS) of dibenzothiophene. The soft acid-soft base interaction between Mo metal and thiol groups enhanced proportionately the metal’s dispersion on the thiol containing support. The thermal decomposition of thiols to generate H2S result in slow and uniform sulfidation of the NiMo to form the NiMoS catalyst. This approach of in-situ generation of H2S for sulfidation provides a promising green method of activating the HDS catalysts without direct use of H2S. Key: hydrodesulfurization; sulfidation; thiol; silica; dibenzothiophene

Aiming at developing a simple, feasible method for SO2 and NOx removal, in this work, various doping amounts of heteropolyacid and heteropolyacid salts were prepared and used in wet absorption for simultaneous removal of SO2 and NO. The desulfurization and denitrification performance was evaluated by investigating dynamic SO2 and NO absorption in a simulated reactor containing a heteropoly compound (HPC) solution along with various factors influencing the reaction. The results demonstrate that this system had a high removal efficiency of SO2 and modest NO removal. The amount of Wolfram (W) doping and the pH of the solution affecting the removal performance was studied, and a stable SO2 removal efficiency higher than 95% was obtained for HPW1Mo at a pH value of 5.5. In addition, the desulfurization performance of NaPWMo with a 50% removal efficiency was higher than that of the HPWMo solution (20%) after a 60 min reaction time. A high concentration of the NaPWMo solution and the presence of O2 were beneficial to desulfurization at room temperature. In addition, the removal efficiency of SO2 or NO by NaPWMo was only affected by its own gas concentration rather than their mutual influences on each other. This work should be beneficial to the optimization leading to the development of simultaneous desulfurization and denitrification systems in practical applications.

NiMo/SiO2 hydrodesulfurization catalyst prepared through the polyoxometalate route using Keggin type phosphomolybdates has high activity in HDS of thiophene at 350–400 °C and 1 bar pressure. The NiMo/SiO2 pre-catalyst retains intact Keggin structure of phosphomolybdic polyoxometalate, which transforms on stream into a NiMo sulfidic active phase. The pre-catalyst also possesses Bronsted and Lewis acidity, which is lost during the HDS reaction. This catalyst undergoes faster sulfidation and shows higher thiophene conversion and higher butene selectivity than conventional industrial NiMo/Al2O3 catalyst with similar Mo loading. The polyoxometalate catalyst preparation route is therefore considered to be a performance enhancement methodology for HDS catalysis.

Deoxygenation and decomposition of ethers and esters, including anisole, diisopropyl ether (DPE), and ethyl propanoate (EP), was investigated using bifunctional metal–acid catalysis at a gas–solid interface in the presence and absence of hydrogen. The bifunctional catalysts studied comprised Pt, Ru, Ni, and Cu as the metal components and Cs2.5H0.5PW12O40 (CsPW), an acidic Cs salt of Keggin-type heteropoly acid (HPA) H3PW12O40, as the acid component, with the main focus on Pt–CsPW catalyst. It was found that bifunctional metal–acid catalysis in the presence of H2 is more efficient for ether and ester deoxygenation than the corresponding monofunctional metal and acid catalysis and that metal- and acid-catalyzed pathways play different roles in these reactions. With Pt-CsPW, hydrodeoxygenation of anisole, a model for the deoxygenation of lignin, occurred with 100% yield of cyclohexane under very mild conditions (60–100 °C and 1 bar of H2). This catalyst had the highest activity in anisole deoxygenation for a gas-phase catalyst system reported so far. The catalyst activity decreased in the order of metals: Pt ≫ Ru > Ni > Cu. For HPA-catalyzed DPE and EP decomposition, relationships between the turnover reaction rate (turnover frequency) and the HPA acid strength were found, which can be used to predict the activity of acid catalysts in these reactions.

The cesium salt of tungstophosphoric heteropoly acid, Cs2.5H0.5PW12O40, is an active and environmentally friendly heterogeneous catalyst for the liquid-phase acetylation of nopol and several biomass-derived terpenic alcohols (i.e., α-terpineol, nerol, geraniol, linalool, menthol, isoborneol, perillyl alcohol, carveol, isopulegol, carvacrol and nerolidol) with acetic anhydride. The resulting flavor and fragrance acetic esters, which are widely used in perfumery, household and food products, are obtained in good to excellent yields. The reactions occur at room temperature with low catalyst loadings without substantial catalyst leaching and can be performed with stoichiometric amounts of an acetylating agent in solvent free systems.

Alkylaminophosphazenes (RPN) are efficient and tuneable phase-transfer agents for environmentally benign biphasic oxidation with hydrogen peroxide catalysed by polyoxometalates (POMs). Substituent groups on the phosphazene ring can be varied to modify the phase-transfer efficiency of RPN for use in water–organic two-phase systems. Active phosphazene–polyoxometalate aggregates that self-assemble in situ from RPN and Keggin POMs, such as PMo12O403− and PW12O403−, were found to be efficient and recyclable catalysts for the oxidation of benzothiophenes and the epoxidation of alkenes with hydrogen peroxide. Lipophilic phosphazene cations present in these aggregates render the POM soluble in organic media. Catalyst activity in the biphasic oxidation with H2O2 varies with the RPN substituent alkylamino groups with respect to the solvent system used. The activity decreases in the series of POMs: PMo12O403−>PW12O403−≫SiW12O404− irrespective of the solvent system used.

Dehydration of methanol to dimethyl ether (DME) was studied at a gas/solid interface over a wide range of bulk and supported Bronsted acid catalysts based on tungsten Keggin heteropoly acids (HPA) and compared with the reaction over HZSM-5 zeolites (Si/Al = 10–120). Turnover rates for these catalysts were measured under zero-order reaction conditions. The HPA catalysts were demonstrated to have much higher catalytic activities than the HZSM-5 zeolites. A good correlation between the turnover rates and catalyst acid strengths, represented by the initial enthalpies of ammonia adsorption, was established. This correlation holds for the HPA and HZSM-5 catalysts studied, which indicates that the methanol-to-DME dehydration with both HPA and HZSM-5 catalysts occurs via the same (or similar) mechanism and the turnover rate of methanol dehydration for both catalysts is primarily determined by the strength of catalyst acid sites, regardless of the catalyst pore geometry.

Bulk and supported hydrodesulfurization catalysts based on Mo and W and containing Co or Ni as promoters and phosphorus as a modifier are prepared through the polyoxometalate route using Keggin type phosphomolybdates and phosphotungstates and tested in the HDS of thiophene at 350–400 °C and 1 bar pressure. The corresponding oxidic pre-catalysts retain intact Keggin structure of the parent polyoxometalates and possess Bronsted and Lewis acidity. In the course of sulfidation, the oxidic pre-catalysts transform into an active sulfidic phase with the loss of Keggin structure and catalyst acidity. Catalyst activity increases in the order of supports: SiO 2 2 2 O 3 . CoMoP/γ-Al 2 O 3 catalyst prepared through the polyoxometalate route shows higher HDS activity and butene selectivity than industrial catalyst of comparable composition. The results indicate that polyoxometalate catalyst preparation route can be considered a performance enhancement methodology for HDS catalysis.

Dehydration of MeOH to dimethyl ether and EtOH to diethyl ether and ethene was studied at the gas-solid interface in the presence of bulk and SiO2-supported Keggin heteropoly acids (HPAs) H3PW12O40 (PW) and H4SiW12O40 (SiW) as catalysts. The catalysts were prepared by HPA impregnation from water and MeOH. Their acid strength, texture and structural integrity was characterised using NH3 adsorption calorimetry, BET, XRD and DRIFT spectroscopy. The strength of acid sites in HPA/SiO2 catalysts increased monotonously with HPA loading. In the dehydration of MeOH and EtOH, the turnover reaction rate for PW catalysts was higher than for SiW catalysts in agreement with their acid strength. HPA catalysts prepared from water and MeOH had a very close acid strength and showed similar activities in alcohol dehydration. The steady-state catalyst activity was found to correlate with the density of catalyst proton surface sites rather than with the HPA loading. This indicates that alcohol dehydration occurred via a mechanism of surface-type HPA catalysis at the gas-solid interface rather than a bulk-type (pseudo-homogeneous) catalysis.

One-pot conversion of mechanically activated cellulose to sorbitol was investigated over bifunctional catalysts based on Ru (0.6, 1 and 3 wt.%) and cesium salts of heteropoly acids (HPA) Cs2.1H0.9PW12O40 and Cs3HSiW12O40 (Cs-PW and Cs-SiW, respectively). The maximal yield of sorbitol equal to 59 % and selectivity 94 % were achieved over the 1%Ru/Cs3HSiW12O40 catalyst. Physicochemical and catalytic data showed that the rate-determining step, i.e. the hydrolysis of cellulose, depended on the surface acidity of catalysts, whereas Ru content in catalyst affected both the hydrolysis and the hydrogenation steps. The kinetic parameters for one-pot conversion of cellulose were determined by mathematical modeling approach and were successfully used for the prediction of the yields of sorbitol and mannitol.

Gas-phase hydrogenation of a wide range of ketones to alkanes, including hydrogenation of aliphatic ketones and acetophenone, was investigated using bifunctional metal–acid catalysis. The catalysts were comprised of a metal (Pt, Ru, Ni, and Cu) supported on acidic caesium salt of tungstophosphoric heteropoly acid Cs2.5H0.5PW12O40 (CsPW). The reaction occurred via a sequence of steps involving hydrogenation of ketone to alcohol on metal sites followed by dehydration of alcohol to alkene on acid sites and finally hydrogenation of alkene to alkane on metal sites. Catalyst activity decreased in the order: Pt > Ru >> Ni > Cu. Pt/CsPW showed the highest catalytic activity, giving almost 100% alkane yield at 100 °C and 1 bar pressure. Evidence is provided that the reaction with Pt/CsPW at 100 °C is limited by ketone-to-alcohol hydrogenation, whereas at lower temperatures (≤60 °C) by alcohol dehydration yielding alcohol as the main product. The catalyst comprised of a physical mixture of Pt/C + CsPW was found to be highly efficient as well, which indicates that the reaction is not limited by migration of intermediates between metal and acid sites in the bifunctional catalyst.

The alkylation of benzene with propane to yield isopropylbenzene proceeds with high selectivity over bifunctional metal–acid catalysts comprising Pt and Keggin heteropoly acid in a fixed-bed reactor at 250–350 °C and 1 bar pressure. Most efficiently the reaction occurs over Pt/H4SiW12O40/SiO2 catalyst at 300 °C, giving isopropylbenzene with 90–93% selectivity at 6–8% benzene conversion, significantly exceeding the efficiency of previously reported Pt/HZSM-5 catalyst. The alkylation proceeds through bifunctional reaction pathway including dehydrogenation of propane to propene (1) on Pt sites followed by benzene alkylation with propene (2) on acid sites. At Pt loadings above 0.5%, step 1 is at fast quasi-equilibrium and step 2 is the rate-limiting one.

Bulk Zn(II)-Cr(III) mixed oxides with a Zn/Cr atomic ratio of 1:1–20:1 were found to be active catalysts for the gas-phase ketonisation of carboxylic acids (acetic and propionic) to form acetone and 3-pentanone, respectively, at 300–400 °C and ambient pressure. Zn-Cr (10:1) oxide showed the best performance, significantly exceeding that of the parent oxides ZnO and Cr2O3. The catalytic activity was further enhanced by supporting Zn-Cr (10:1) oxide on TiO2 and γ-Al2O3. With 20%Zn-Cr/Al2O3, ketonisation of propionic acid occurred with 97% selectivity to 3-pentanone at 99% conversion at 380 °C. Zn-Cr oxides were characterised by BET, XRD, DRIFTS of pyridine and acetic acid adsorption and microcalorimetry of ammonia adsorption. From DRIFTS, carboxylic acid adsorbed dissociatively on Zn-Cr oxide to form a surface metal carboxylate in bidentate bridging bonding mode. A mechanism for ketonisation of carboxylic acids via β-ketoacid intermediate route has been proposed.

Polyisobutylene (PIB) oligomer-bound amines render Keggin polyoxometalates (POM) heptane soluble, making them efficient and recyclable catalysts for environmentally benign biphasic oxidations with hydrogen peroxide. This is illustrated using both oxidative desulfurization and alkene epoxidation reactions that can be efficiently carried out in a heptane–water two-phase system occurring through facile phase transfer of POM by the amine terminated PIB oligomer.

Dehydration of ethanol was studied at a gas–solid interface over a wide range of solid Bronsted acid catalysts based on Keggin-type heteropoly acids (HPAs) in a continuous flow fixed-bed reactor in the temperature range of 90–220 °C focussing on the formation of diethyl ether (DEE). The catalysts included H3PW12O40 (HPW) and H4SiW12O40 (HSiW) supported on SiO2, TiO2, Nb2O5 and ZrO2 with sub-monolayer HPA coverage, as well as bulk acidic Cs salts of HPW (Cs2.5H0.5PW12O40 and Cs2.25H0.75PW12O40) and the corresponding core–shell materials with the same total composition (15%HPW/Cs3PW12O40 and 25%HPW/Cs3PW12O40, respectively) comprising HPW supported on the neutral salt Cs3PW12O40. The ethanol-to-DEE reaction was found to be zero order in ethanol in the range of 1.5–10 kPa ethanol partial pressure. The acid strength of catalysts was characterised by ammonia adsorption microcalorimetry. A fairly good correlation between the catalyst activity (turnover frequency) and the catalyst acid strength (initial enthalpy of ammonia adsorption) was established, which demonstrates that Bronsted acid sites play important role in ethanol-to-DEE dehydration over HPA catalysts. The acid strength and the catalytic activity of core–shell catalysts HPW/Cs3PW12O40 did not exceed those of the corresponding bulk Cs salts of HPW with the same total composition, which contradicts the literature claims of the superiority of the core–shell HPA catalysts.

The cesium salt of tungstophosphoric heteropoly acid, Cs2.5H0.5PW12O40, is an active and environmentally friendly solid-acid catalyst for the liquid-phase alkoxylation of widespread monoterpenes, such as camphene, limonene, α-pinene, and β-pinene. These reactions provide isobornyl or α-terpenyl ethers, useful as fragrances, in good to excellent yields. The reactions are equilibrium-controlled and occur with high catalyst turnover numbers (TONs) up to 1500–4200 without catalyst leaching. Heteropoly acid H3PW12O40 also efficiently catalyzes the alkoxylation of these monoterpenes under homogeneous conditions with TONs up to 1500–11 300.

Metal oxides such as Nb2O5, Cr2O3, and especially a ZnIICrIII mixed oxide are demonstrated to be highly active and recyclable heterogeneous catalysts for Prins condensation, which provides a clean, high-yielding route for the synthesis of nopol through the condensation of biorenewable β-pinene with paraformaldehyde. ZnCr mixed oxide with an optimum Zn/Cr atomic ratio of 1:6 gave 100 % nopol selectivity at 97 % β-pinene conversion, with the catalyst easily recovered and recycled. The acid properties of Nb2O5 and ZnCr mixed oxide were characterized by the diffuse reflectance IR Fourier transform spectroscopy of adsorbed pyridine and ammonia adsorption microcalorimetry. An appropriate combination of acid–base properties of ZnCr mixed oxide is believed to be responsible for its efficiency.

We demonstrate, for the first time, the application of FTIR spectroscopic imaging approach in situ to monitor the precipitation process of oil asphaltenes, induced by n-heptane under flow using microfluidic devices. The aggregation of asphaltenes induced by n-heptane flow with subsequent precipitation and formation of the deposits was studied for solution containing 5 wt % of asphaltenes in benzene. The FTIR spectroscopic approach with an array detector allowed us to assess the spatial distribution of the chemical components and their amounts in the system and display the process of aggregates formation with a spatial resolution of few micrometres. This chemical imaging technique shows that the flow of heptane results in non-equilibrium condition when the local content of the flocculants reaches the threshold amount needed for the asphaltenes aggregation. The relatively slow process of heptane diffusion into the benzene induces the asphaltenes aggregation followed by their precipitation and compaction. Fast asphaltene aggregation process under heptane flow leads to the formation of the deposit firmly fixed to the surface, while the precipitates formed during the diffusion process of heptane into the benzene can be easily taken from the channel. The FTIR spectroscopic imaging of the deposits formed revealed the spatial inhomogeneity of the precipitated asphaltenes in the direction of the heptane flow in microfluidic channel which is reflected in their different chemical composition and the presence of different functional groups (CH2–CH3, C O, S O). In particular, it was found that asphaltenes of different types and different CH2/CH3 ratios gradually start to precipitate in the direction of n-heptane flow. The data obtained demonstrate the importance of local concentration of flocculants as well as local characteristics of the system for asphaltenes aggregation, and overall precipitation process in flow regime.

Terpenes are an abundant class of natural products, which is important for flavor and fragrance industry. Many acid catalyzed reactions used for upgrading terpenes still involve mineral acids as homogeneous catalysts and/or toxic solvents. Heteropoly acids represent a well-established eco-friendly alternative to conventional acid catalysts. As these reactions are usually performed in the liquid phase, solvents play a critical role for the process sustainability. In the present work, we developed a catalytic route to valuable fragrance ingredients, dihydrocarvone and carvenone, from limonene oxide by its isomerization using silica-supported tungstophosphoric acid as a heterogeneous catalyst and dialkylcarbonates as green solvents. The reaction pathway can be switched between dihydrocarvone and carvenone (obtained in 90% yield each) simply by changing the reaction temperature. In addition, we developed an efficient method for kinetic separation of trans-limonene oxide from commercial cis/trans-limonene oxide mixture and stereoselective synthesis of trans-dihydrocarvone.

SiO2-containing materials (quartz, Pyrex glass, silica gel, and H-Y zeolite) react slowly with methanol at 350 °C under both supercritical and gas-phase conditions. The amount of SiO2 reacted with supercritical methanol depends on the kind of the material and is varied from 0.05 wt% for quartz sand to 4.0 wt% for wide-porous silica gel for 5 h of the reaction. The main products of the reaction are methyl orthosilicates, mainly tetramethyl orthosilicate. N-Unsubstituted 1H-indole, 1H-benzimidazole, and 1H-indazole additives considerably increase the amount of reacted SiO2-containing material. Noteworthy, quartz sand “solubility” is increased ca 14-fold when indole is used at the same reaction conditions. These benzazoles provide a nucleophilic assistance to the reaction between SiO2 and methanol. During the assistance, the azole ring is methylated by methanol, and the participation of SiO2-surface or tetramethyl orthosilicate molecule facilitates the alkylation reaction of benzazole used.

The liquid-phase isomerization of limonene oxide was studied in the presence of heteropoly acid catalysts in aprotic solvents in homogeneous and heterogeneous systems. Among the catalysts were bulk and silica-supported tungstophosphoric acid H3PW12O40 and its acidic Cs salt Cs0.5H0.5PW12O40 (CsPW). The reaction gave dihydrocarvone, a valuable fragrance intermediate, as the main product with turnover numbers of up to 8000. The nature of the solvent had a strong effect on reaction rate and selectivity. CsPW (0.1 mol%) was found to be a highly efficient and truly heterogeneous catalyst for this reaction, providing 82% yield of dihydrocarvone in 1,4-dioxane as a solvent under ambient conditions. This simple catalytic method represents economically attractive route to industrially important compounds starting from bio-renewable substrates easily available from essential oils.

Reaction pathways of the gas-phase deoxygenation of propionic acid in the presence of heteropoly acid and bifunctional metal-loaded heteropoly acid catalysts were investigated in a fixed-bed reactor at 250–400 °C in flowing H 2 or N 2 . Silica-supported H 3 PW 12 O 40 (HPW) and bulk acidic salt Cs 2.5 H 0.5 PW 12 O 40 (CsPW), both in H 2 and in N 2 , exhibited ketonisation activity between 250 and 300 °C to yield 3-pentanone, CsPW being more selective than HPW. At 400 °C, HPW and CsPW were active for decarbonylation and decarboxylation of propionic acid to yield ethene and ethane, respectively. Loading Pd or Pt onto CsPW greatly enhanced decarbonylation in flowing H 2 but had little effect in N 2 . Similar performance exhibited Pd/SiO 2 and Pt/SiO 2 , giving almost 100% selectivity to ethene in H 2 . These results are consistent with hydrodeoxygenation of propionic acid on Pd and Pt, suggesting that hydrogenolysis of C C bond plays essential role. In contrast to the Pd and Pt catalysts, Cu catalysts, Cu/CsPW and Cu/SiO 2 , were both active in hydrogenation of C O bond to yield propanal and 1-propanol. Turnover rates of propionic acid conversion on metal catalysts followed the order Pd > Pt > Cu for both CsPW-supported and silica-supported metal catalysts.

It was demonstrated that iron molybdate catalysts for methanol oxidation can be prepared using Fe(II) as a precursor instead of Fe(III). This would allow for reduction of acidity of preparation solutions as well as elimination of Fe(III) oxide impurities which are detrimental for the process selectivity. The system containing Fe(II) and Mo(VI) species in aqueous solution was investigated using UV–Vis spectroscopy. It was demonstrated that three types of chemical reactions occur in the Fe(II)–Mo(VI) system: (i) formation of complexes between Fe(II) and molybdate(VI) ions, (ii) inner sphere oxidation of coordinated Fe(II) by Mo(VI) and (iii) decomposition of the Fe–Mo complexes to form scarcely soluble Fe(III) molybdate, Mo(VI) hydrous trioxide and molybdenum blue. Solid molybdoferrate(II) prepared by interaction of Fe(II) and Mo(VI) in solution was characterized by EDXA, TGA, DTA and XRD and a scheme of its thermal evolution proposed. The iron molybdate catalyst prepared from Fe(II) precursor was tested in methanol-to-formaldehyde oxidation in a continuous flow fixed-bed reactor to show similar activity and selectivity to the conventional catalyst prepared with the use of Fe(III).

Methyl isobutyl ketone (MIBK) can be viewed as a key intermediate for the conversion of biomass-derived acetone – the by-product of biobutanol production – to transportation fuel. Zeolite H-ZSM-5 doped with Pt nanoparticles was found to be a highly efficient catalyst for gas-phase hydrogenation of MIBK to methylpentanes with >99% yield at 200 °C. The reaction proceeds via bifunctional metal-acid catalysed pathway involving MIBK hydrogenation to 4-methyl-2-pentanol (MP-ol) on metal sites followed by MP-ol dehydration on acid sites to form olefin and finally olefin hydrogenation to 2-methylpentane (2MP) on metal sites, with all three steps occurring on a single catalyst bed. 2MP thus obtained underwent isomerisation over bifunctional Pt/H-ZSM-5 catalyst to give a mixture of 2- and 3-methylpentanes in a ratio of 83:17. The catalyst did not show any deactivation for at least 16 h on stream.

Methylation reaction of indole was studied in supercritical methanol (350 °C, 215 atm) catalyzed by TMOS and TEOS. Use of both orthosilicates shows the same result of indole methylation. The indole conversion is ∼30% for 5 h of the reaction with and without catalysts. But catalytic reaction is more high-selective on 3-methyl-1H-indole formation – 95–96 mol% against 60 mol% for non-catalytic methylation. Indole conversion in catalytic reaction increases by a quarter (with no change of selectivity) when two equivalents of water are added into reaction mixture. Methylating system was assumed to be the TMOS–MeOH, and methylation proceeds via cyclic, multi-centered transition state (TS). The TS involves molecules of indole, TMOS, methanol, and water (if used), which are orientated in a certain way to each other by hydrogen and coordinate bonding. The reaction does not occur in supercritical ethanol or isopropanol with and without using the catalysts.

Kinetics of isopropanol dehydration at a gas–solid interface over a range of bulk and supported Bronsted acid catalysts based on H 3 PW 12 O 40 (HPW) Keggin-type heteropoly acid was studied in a continuous flow fixed-bed reactor in the temperature range of 55–135 °C and isopropanol partial pressure of 0.94–5.52 kPa. The bulk catalysts included HPW itself and its Cs acid salts Cs n H 3− n PW 12 O 40 (Cs n H 3− n PW). The supported catalysts comprised of 15 wt.% HPW supported on SiO 2 , TiO 2 , ZrO 2 and Nb 2 O 5 . Under the conditions studied, the reaction was found to be of zero order in isopropanol. The turnover rate decreased in the order HPW > Cs 2.5 H 0.5 PW ≈ Cs 2 HPW > HPW/SiO 2 > HPW/TiO 2 > HPW/Nb 2 O 5 ≈ HPW/ZrO 2 , which is in line with the acid strength of these catalysts. The true activation energies E and pre-exponential factors A obtained from zero-order kinetics, were found to exhibit a compensation linear relationship ln A = mE + c . Moreover, the bulk and supported catalysts exhibited different compensation plots. This is suggested to be due to the different chemical structure of Bronsted acid sites in these catalysts, resulting in differing reaction mechanisms. The bulk catalysts possess strong surface H + sites located on peripheral (bridging) oxygen atoms in the Keggin unit, whereas supported HPW catalysts have weaker H + sites probably located on oxygen atoms of support. Consequently, on the bulk catalysts, isopropanol dehydration is suggested to occur via E1 elimination pathway, whereas on the supported catalysts it might also involve a contribution of E2 elimination pathway.

Aryl alcohols are employed as feedstock for the Heck reaction. Keggin-type heteropolyacids catalyse the selective dehydration of the alcohols to styrenes, which, in one-pot, undergo palladium-catalysed Heck arylation with aryl bromides, affording broadly functionalised stilbenes. The choice of solvent is critical for the cascade dehydration–Heck reaction, with electron-rich aryl alcohols preferring a basic medium while electron-deficient ones demanding solvents of lower basicity.

New data on enthalpy and entropy contributions to the energy barrier of β-pinene thermal isomerization were obtained. The rate of β-pinene conversion is higher in supercritical EtOH (P = 120 atm) than in the gas phase (P ≤ 1 atm, without solvent, or for inert carrier gas N2) at equal temperatures. The highest activation energy EΣ of total β-pinene conversion is also observed in reactions in the supercritical (sc) condition. Activation parameters ΔHΣ#, ΔSΣ#, and ΔGΣ# depend strongly on the reaction pressure. Thus, at P ≤ 1 atm (gas-phase reaction) the values of ΔSΣ# are negative, while at sc conditions at P = 120 atm is positive. The linear dependences lnkΣ0 − EΣ and ΔSΣ# − ΔSΣ# indicate an isokinetic relation (IKR) and enthalpy-entropy compensation effect (EEC). The isokinetic temperature was calculated (Tiso = 605.5 ± 22.7 K). It was shown that elevation of temperature reduces the value of ΔGΣ#(T) upon sc thermolysis only, whereas in all gas-phase reactions ΔGΣ#(T) increases. At equal reaction temperatures, the greatest values of Keq#(T) proved to be typical for thermolysis in sc-EtOH. We hypothesize that the rate of total β-pinene conversion increases dramatically due to a considerable shift in equilibrium toward higher concentrations of activated complex yTS#. A detailed analysis of activation parameters shows that the IKR and EEC coincide, evidence of a common mechanism of β-pinene conversion observed under different reaction conditions, including thermolysis in sc-EtOH.