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Catalytic synergism was observed for a bimetallic Pd−Ir catalyst supported on activated carbon for chemoselective hydrogenation of 5‐hydroxymetahyl furfural (5‐HMF) to 2, 5‐(bishydroxymethyl) furan (BHMF) with complete conversion and 97 % selectivity under very mild reaction conditions. The structural characterization like XRD, N2 sorption, FE‐SEM and TEM suggested formation of fine nanoparticles (1.95–3.08 nm) having very higher surface area, uniform distribution and mesoporous nature of the material. XPS spectra and Pyridine‐IR spectroscopy revealed formation of Pd‐PdO and Ir/IrO2/IrO3 interface on the catalytic surface along with strong Brönsted acidic sites which were responsible for high efficiency of catalyst at 80 °C, 100 psig H2 pressure at 5‐HMF/Catalyst=20 and within 2.5 h of reaction time. A plausible reaction mechanism is also elucidated based on structure activity correlation. [ABSTRACT FROM AUTHOR]

2‐Methyltetrahydrofuran is a valuable commercial product that can be obtained by direct hydrogenation of furfural. In the present study, among several carbon supported bimetallic Ir−Ni catalysts with different loadings screened, 4% Ir‐4% Ni/C catalyst showed excellent activity in terms of direct conversion (99%) to 2‐MeTHF with a maximum selectivity of ∼74% at 220 °C and 750 psig, suppressing the formation of side chain as well as ring opening products. The catalytic activity was found to be mainly affected by catalyst preparation methods, metal loadings, surface composition, temperature, pressure and catalyst loading. HR‐TEM and STEM revealed well dispersed Ir−Ni NPs having the particle sizes in the range of 2 to 5 nm. Different phases of Ir i. e. Ir° and IrO2 as well as oxygen vacancies were found to be responsible for hydrogenation of furfural to 2‐methyl furan while, Ni° and NiO were responsible for further hydrogenation to 2‐MeTHF. The synergic effect between Ir and Ni was established through XPS, H2‐TPR analysis. With the help of some control experiments, the plausible reaction pathway was also proposed. The catalyst prepared by co‐impregnation method found more effective than prepared by sequential addition method. At lower Ni loadings of 1% and 2%, low temperature of 160 °C as well as at low H2 pressure of 250 psig, mixture of furfuryl alcohol and 2‐methyl furan were formed selectively. Catalyst could be successfully reused up to 3 times without leaching of metals. [ABSTRACT FROM AUTHOR]

A non-noble bimetallic catalyst Cu–Fe (1 : 2) was magnetically recoverable, highly selective and efficient for 5-(hydroxymethyl) furfural (5-HMF) hydrogenation to 2,5-dimethyl furan (DMF). The structure–activity correlation was established by characterising the prepared catalyst by XRD, XPS, TEM, ESEM, BET surface area, N2-adsorption, NH3-TPD, pyridine-IR and H2-TPR measurements. The high catalytic efficiency was attributed to the oxophilic nature and Lewis acidity of Fe, whereas the selectivity towards DMF was attributed to the Brønsted acidity of CuO and its affinity towards the C–O bond which was further confirmed by NH3-TPD and Py-IR analyses. XPS and XRD revealed the presence of Cu/CuFe2O4 species which catalyzed the hydrogenolysis pathway. TEM and SEM images evidenced the presence of a Cu–Fe nanomorph in which Cu/CuFe2O4 was present. The size of the Cu–Fe nanomorph was found to be between 15.4–17.6 nm. Under the optimised reaction conditions, the highest conversion of 97% and selectivity of 93% were achieved. [ABSTRACT FROM AUTHOR]

The combination of supported rhodium metal catalysts and supercritical carbon dioxide solvent was effective for the stereoselective ring hydrogenations of aromatic compounds at low temperature. Higher solubility of hydrogen in supercritical carbon dioxide provides higher concentration of hydrogen on the rhodium surface, but lower that of the intermediate on rhodium surface, which suppresses the flipping of surface intermediate, leading to higher catalyst activities and cis selectivities to the corresponding ring‐hydrogenated products as compared with those in organic solvents. [ABSTRACT FROM AUTHOR]

Various iridium supported carbon catalysts were prepared and screened for the direct hydrogenation of furfural (FFR) to 2-methyl furan (2-MF). Amongst these, 5% Ir/C showed excellent results with complete FFR conversion and highest selectivity of 95% to 2-MF at a very low H2 pressure of 100 psig. Metallic (Ir°) and oxide (IrO2) phases of Ir catalyzed the first step hydrogenation involving FFR to FAL and subsequent hydrogenation to 2-MF, respectively. This was confirmed by XPS analysis and some control experiments. At a low temperature of 140 °C, almost equal selectivities of FAL (42%) and 2-MF (43%) were observed, while the higher temperature (220 °C) favored selective hydrodeoxygenation. At optimized temperature, 2-MF was formed selectively while higher pressure and higher catalyst loading favored ring hydrogenation of furfural rather than side chain hydrogenation. With the combination of several control experimental results and detailed catalyst characterization, a plausible reaction pathway has been proposed for the selective formation of 2-MF. The selectivity to various other products in FFR hydrogenation can be manipulated by tailoring the reaction conditions over the same catalyst. [ABSTRACT FROM AUTHOR]

Several copper based catalysts were prepared, characterized and evaluated for the hydrogenation of levulinic acid and its methyl ester. Among these, nanocomposites of Cu–ZrO2 and Cu–Al2O3 quantitatively catalyzed the hydrogenation of levulinic acid and its methyl ester to give 90–100% selectivity to γ-valerolactone in methanol and water respectively. Both the Cu–ZrO2 and Cu–Al2O3 nanocomposites were prepared by the co-precipitation method using mixed precursors under controlled conditions. XRD results showed that the main active phase of the reduced Cu–ZrO2 catalyst was metallic copper and particle size was found to be of 10–14 nm by HRTEM. The active metal leaching was at a maximum for the Cu–Al2O3 catalyst in a water medium due to the formation of a copper–carboxylate complex that was blue in colour. Surprisingly, copper leaching was completely suppressed in the case of the Cu–ZrO2 catalyst in methanol in spite of the substrate loading was increased from 5 to 20% w/w. The excellent recyclability of the Cu–ZrO2 catalyst with complete LA conversion and ＞90% GVL selectivity makes it a sustainable process having a commercial potential. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogenation of 2-, 3-, and 4-tert-butylphenols was studied over a charcoal-supported rhodium catalyst in supercritical carbon dioxide (scCO2) solvent, and the results were compared with those in organic solvents. In the hydrogenation of 4-tert-butylphenol, a higher cis ratio for 4-tert-butylcyclohexanol (0.79) was obtained in scCO2 (10 MPa) than in 2-propanol (0.70) and cyclohexane (0.64) under similar conditions of hydrogen pressure (2 MPa) and temperature (313 K). In the case of 2-tert-butylphenol, the cis ratio for 2-tert-butylcyclohexanol was as high as 0.95 in both scCO2 and 2-propanol (hydrogen pressure, 2 MPa; reaction temperature, 313 K). In the case of hydrogenation of 3-tert-butylphenol, the cis ratio decreased with the progression of consecutive hydrogenation of 3-tert-butylcyclohexanone intermediate. In addition, the stereoselectivity to cis-tert-butylcyclohexanols in scCO2 was improved in the presence of hydrochloric acid. It was found that the protons of hydrochloric acid accelerated the hydrogenation of the intermediates, tert-butylcyclohexanones, to the corresponding cis-tert-butylcyclohexanols. The hydrogenation mechanism of tert-butylphenols, particularly the enhanced selectivity to cis-tert-butylcyclohexanols in scCO2, is postulated based on the observed reaction profiles. [Copyright &y& Elsevier]

Abstract: Catalytic ring hydrogenations of naphthalene and 1-naphthol were studied over several supported metal catalysts in supercritical carbon dioxide solvent at low temperature. Higher concentration of hydrogen in supercritical carbon dioxide and lower reaction temperature were responsible for higher catalyst activity and selectivities to the desired partial ring hydrogenated products as compared with those observed in organic solvent for the same catalyst. [Copyright &y& Elsevier]

Abstract: Catalytic hydrogenation of biphenyl to bicyclohexyl, an organic hydrogen storage medium, was examined over supported transition metal catalysts in supercritical carbon dioxide solvent. The yield of bicyclohexyl was almost 100% over the charcoal-supported rhodium (Rh/C) and ruthenium (Ru/C) catalysts at the temperature of 323K, which was much lower than that required for biphenyl hydrogenation in organic solvents (573K). The initial activity was higher over the Rh/C catalyst, while the initial selectivity to bicyclohexyl was higher over the Ru/C catalyst. The conversion of biphenyl increased with increase in hydrogen and carbon dioxide pressures, while the selectivity to bicyclohexyl was independent of hydrogen and carbon dioxide pressures over both catalysts. [Copyright &y& Elsevier]

Catalytic hydrogenation of 3,3,5-trimethyl-2-cyclohexen-1-one (isophorone) was examined over several supported noble metal catalysts in supercritical carbon dioxide. Charcoal supported rhodium and platinum catalysts were found to be active for the isophorone hydrogenation to 3,3,5-trimethylcyclohexanone (dihydroisophorone), but undesirable successive hydrogenation to 3,3,5-trimethylcyclohexanol also proceeded. Supported palladium catalysts were less active than the supported rhodium and platinum catalysts, but were highly selective for dihydroisophorone. [Copyright &y& Elsevier]

The cover feature highlights the distinct advantages of heterogeneously catalyzed multi-phase hydrogenation in supercritical carbon dioxide solvent, resulting in not only easy separation of products and catalyst, but also control of the product selectivity and activity. Hydrogenation, supercritical carbon dioxide, stereoselectivity, rhodium catalyst. [Extracted from the article]

Presents a study which examined the activities of various catalysts for the hydrogenation of tetralin to cis-decalin. Importance of hydrogenation of tetralin for the production of a high performance diesel fuel; Advantages of hydrogenation with supported metal catalysts in supercritical carbon dioxide solvent; Reaction profile for the hydrogenation of tetralin.

Selective ring hydrogenation of naphthols to tetrahydronaphthols and tetralones proceeded at 323 K over a charcoal supported rhodium catalyst in supercritical carbon dioxide. [ABSTRACT FROM AUTHOR]

A charcoal-supported rhodium catalyst was highly active and selective to decalin for the hydrogenation of naphthalene at very low temperature (333 K) under supercritical carbon dioxide. [ABSTRACT FROM AUTHOR]

Naphthalene hydrogenation over activated carbon-supported rhodium metal particles having dispersion between 10 and 30% was studied; the turnover frequencies increased with decreasing dispersion in supercritical carbon dioxide, while were independent of the metal dispersion in n-heptane. [ABSTRACT FROM AUTHOR]

cis-4-tert-Butylcyclohexanol was obtained with a high cis ratio (cis/(cis + trans) = 0.9) in the hydrogenation of 4-tert-butylphenol over a carbon-supported rhodium catalyst along with hydrochloric acid in supercritical carbon dioxide solvent. [ABSTRACT FROM AUTHOR]

Abstract: Activities of graphite-supported rhodium catalysts were examined for the hydrogenation of naphthalene in supercritical carbon dioxide (scCO2) solvent at 313K, and results were compared with those of activated carbon-supported rhodium catalysts. The graphite-supported rhodium catalysts exhibited higher activities on a catalyst-weight basis and higher turnover frequency values for the naphthalene hydrogenation in scCO2 than activated carbon-supported rhodium ones. [Copyright &y& Elsevier]

Abstract: Hydrogenation of benzothiophene-free naphthalene was examined over various transition metal (rhodium, ruthenium, palladium, and platinum) catalysts supported on charcoal in supercritical carbon dioxide (scCO2) solvent at low temperature (313K). Among these, a charcoal-supported rhodium catalyst was found to be the most active, while a charcoal-supported ruthenium catalyst was found to give the highest cis-decahydronaphthalene (cis-decalin) selectivity. A systematic investigation of hydrogenations of naphthalene and tetrahydronaphthanele (tetralin) in scCO2 revealed that naphthalene hydrogenation is a consecutive and cis- and trans-decalin were formed via tetralin. [Copyright &y& Elsevier]

Abstract: Hydrogenation of tetralin was studied over supported rhodium catalysts in supercritical carbon dioxide solvent at 333K. The results were compared with those in an organic solvent and under neat conditions. Higher cis-decalin yield was obtained in supercritical carbon dioxide solvent than under non-supercritical conditions. It was observed that higher hydrogen concentration at the surface in supercritical carbon dioxide solvent led to fast direct hydrogenation of tetralin to cis-decalin; the flipping of the intermediate, octalin, to give trans-decalin could be prevented. [Copyright &y& Elsevier]

The acid functionality of montmorillonite clay K 10 (MMT-K 10) was found to play a key role to give 1,2-pentanediol (1,2-PeDO) in Pd catalysed furfural hydrogenation. Among various Pd loadings on MMT-K 10, 3% Pd/MMT-K 10 catalyst exhibited excellent performance giving almost complete conversion of FFR and the highest selectivity of 66% to 1,2-PeDO. Py-IR of the catalyst evidenced the presence of Brønsted acidity which was responsible in C5-O cleavage of furan ring after the formation of furfuryl alcohol which is the first step intermediate in FFR hydrogenation. At a lower temperature of 140 °C, highest selectivity of 56% was achieved for FAL while increase in temperature to 220 °C, enhanced the selectivity to 1,2-PeDO. Keeping the temperature constant at 220 °C, increase in H 2 pressure from 500 to 750 psig, resulted in decrease in 1,2-PeDO selectivity from 66 to 34% with proportionate increase in THFAL selectivity. Thus as per the requirement, the product selectivities can be tailored by varying the reaction parameters suitably. Several control experiments were also performed the results of which combined with the characterization data allowed to propose a plausible reaction pathway for the formation of 1,2-PeDO. [ABSTRACT FROM AUTHOR]

Supported monometallic (Pt, Ni,) and bimetallic (Ni–Pt)catalysts were prepared for the selective liquid phase hydrogenationof m-chlronitrobenzene to m-chloroaniline(m-CAN). It was found that the use of sodium carbonateas an additive substantially reduced the extent of dehydrohalogenationin the case of monometallic, 1% Pt/C catalyst, to give the highestselectivity of 96% to m-CAN. Ni–Pt bimetalliccatalyst although showed almost complete selectivity (>99%) to m-chloroaniline; its activity was several fold lower thanthat of 1% Pt/C–Na2CO3system. However,compared with Ni monometallic catalyst, bimetallic Ni–Pt showedhigher activity and selectivity due to the presence of electron richsurface metallic Pt stabilized by Ni having lower ionization potentialcompared with Pt. [ABSTRACT FROM AUTHOR]

Two steps involving catalytic hydrogenation of nitrobenzene to phenylhydroxylamine (PHA) in acid medium and its rearrangement to p-aminophenol (PAP) were studied separately in a batch reactor, using a well-characterized 3% Pt/C catalyst. The first step of hydrogenation of nitrobenzene to PHA could be carried out at 303 K and a H2 pressure of 0.69 MPa with complete conversion of nitrobenzene, while the achieved selectivity to PHA was higher than 90% with some formation of aniline, even at lower temperature. The second step of PHA rearrangement to PAP could be achieved under a hydrogen atmosphere at elevated temperature of 353 K to give a maximum selectivity to PAP of 74%. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogenation of 4-alkylphenols was studied over a carbon-supported rhodium catalyst in supercritical carbon dioxide (scCO2) solvent, and the results were compared with those in 2-propanol. Higher selectivities to cis-4-alkylcyclohexanols were obtained in scCO2 than in 2-propanol for the hydrogenation of all 4-alkylphenols tested. In addition, the formation of alkylcyclohexane (dehydroxylated product) was suppressed in scCO2. Stereoselectivities to cis forms were further improved in the presence of hydrochloric acid. [Copyright &y& Elsevier]

Abstract: Catalytic ring hydrogenation of 1- and 2-phenylethanols was studied over several noble metal catalysts supported on charcoal or γ-alumina in supercritical carbon dioxide. The major products formed were corresponding cyclohexylethanols via aromatic ring hydrogenation of 1- and 2-phenylethanols while by products, ethylbenzene and cyclohexylethane were formed in minor quantities due to dehydroxylation reaction. A charcoal supported ruthenium catalyst gave the highest selectivity to (>80%) cyclohexylethanols among the other catalysts tested in this study at 323K in supercritical carbon dioxide solvent. [Copyright &y& Elsevier]

Catalytic hydrogenation of 2-tert-butylphenol over a charcoal-supported rhodium catalyst in carbon dioxide solvent at 313 K was studied in a batch reactor. To elucidate the effect of carbon dioxide pressure on the initial rate of reaction, the phase behavior of the ternary (2-tert-butylphenol−carbon dioxide−hydrogen) system was separately observed with a view cell, and the calculations of vapor−liquid equilibrium and compositions in the vapor and liquid phases inside the reactor were carried out using the Peng−Robinson equation of state. The hydrogenation behavior in the carbon dioxide solvent is discussed based on the phase behavior of the ternary system. [ABSTRACT FROM AUTHOR]