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Stephan Jaenicke - One of the best experts on this subject based on the ideXlab platform.
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Post-synthesized zirconium-containing Beta zeolite in Meerwein–Ponndorf–Verley Reduction: Pros and cons
Applied Catalysis A: General, 2015Co-Authors: Jie Wang, Kazu Okumura, Stephan Jaenicke, Gaik-khuan ChuahAbstract:Abstract Zr-Beta zeolite was prepared by a two-step post-synthesis method involving dealumination of Al-Beta followed by wet impregnation with Zr(NO3)4. Compared with Zr-Beta formed under fluoride-mediated hydrothermal conditions, the post-synthesized samples had smaller particle size and stronger Lewis acidity. The materials were tested as catalysts for Meerwein–Ponndorf–Verley Reduction. In the Reduction of 4-tert-butylcyclohexanone, it exhibited the same excellent stereoselectivity toward cis-4-tert-butylcyclohexanol (>99%) as the HF-synthesized Zr-Beta, but had a lower TOF. Because of the higher density of zirconium sites and the nanosized crystallites, it was a more effective catalyst for the MPV Reduction of 1,4-cyclohexanedione, bulky aldehydes and aromatic ketones. However, it is more susceptible to poisoning by water adsorption because of its hydrophilic nature. The easily scalable synthesis method allows a faster preparation of metal-substituted Lewis acid zeolites, although differences in textural and chemical properties should be taken into consideration when the material is applied as a catalyst.
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Zirconium–Beta zeolite as a robust catalyst for the transformation of levulinic acid to γ-valerolactone via Meerwein–Ponndorf–Verley Reduction
RSC Adv., 2014Co-Authors: Jie Wang, Stephan Jaenicke, Gaik-khuan ChuahAbstract:Zr–Beta zeolite is a robust and active catalyst for the Meerwein–Ponndorf–Verley Reduction of levulinic acid to γ-valerolactone, a versatile intermediate for bio-fuels and chemicals. In a batch reactor, γ-valerolactone was formed with a selectivity of >96%. In a continuous flow reactor, >99% yield of γ-valerolactone was obtained with a steady space-time-yield of 0.46 molGVLgZr−1 h−1 within 87 h, on a par with that of noble metal based catalysts. The high activity of this catalyst was attributed to the presence of Lewis acidic sites with moderate strength. Due to the relatively few basic sites, it is not poisoned by the acidic reactant. Its robustness in liquid and gas phase reactants coupled with good thermal stability makes Zr–Beta a green regenerable catalyst that can be used directly on levulinic acid without the need for derivatization.
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Stereoselective cascade hydrogenation of 4-tert-butylphenol and p-cresol over Zr-zeolite beta-supported rhodium
Journal of Catalysis, 2007Co-Authors: Yuntong Nie, Stephan Jaenicke, Herman Van Bekkum, Gaik-khuan ChuahAbstract:Abstract The hydrogenation of 4- tert -butylphenol and p -cresol was investigated over Zr-beta-supported rhodium catalysts. By designing a suitable bifunctional catalyst, the intermediate, 4-alkylcyclohexanone, formed by metal-catalyzed hydrogenation of 4-alkylphenol, could be reduced via the highly stereoselective Meerwein–Ponndorf–Verley Reduction over zirconium Lewis acid sites. Thus, in the presence of 2-propanol as solvent and MPV reductant, a high stereoselectivity to cis -4-alkylcyclohexanol was observed. Over 0.5% Rh/Zr-beta, 4- tert -butylphenol, and p -cresol were hydrogenated to the cis -alcohols with 95 and 89% stereoselectivity, respectively. A higher metal loading or the use of solvents such as hexane or tert -butanol led to a lower stereoselectivity, as metal-catalyzed hydrogenation predominated. Similarly, the cis : trans alcohol ratio was lower for rhodium supported on zirconia or Al-beta. Compared with rhodium, palladium was less active in the hydrogenation of the 4-alkylphenols, requiring a higher hydrogen pressure and temperature. A two-step cascade reaction mechanism is proposed for the conversion of 4-alkylphenols to cis -4-alkylcyclohexanols.
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Selective Meerwein–Ponndorf–Verley Reduction of α,βα,β-unsaturated aldehydes over Zr-zeolite beta
Journal of Catalysis, 2006Co-Authors: Yongzhong Zhu, Gaik-khuan Chuah, Stephan JaenickeAbstract:Zr-zeolite beta with Si/Zr ratio of 75–200, as well as zeolite beta with both Zr (Si/Zr ratio of 100) and Al (Si/Al ratios of 100 and 25), were synthesized in a seeded synthesis using HF as the mineralizer. The Al-free Zr-zeolite beta was found to catalyse the MPV Reduction of α,βα,β-unsaturated aldehydes to the corresponding alcohols with high selectivity. In the Reduction of cinnamaldehyde to cinnamyl alcohol, TONs of 55–77 mol mol−1Zr h−1 were obtained with selectivity >98%>98%. Zr-zeolite beta maintained good activity and selectivity in the presence of water and benzoic acid. Reuse of the catalyst by washing with 2-propanol or recalcination led to recovery of activity. For the Al-containing Zr-zeolite beta, 27Al NMR spectra showed that Al was incorporated into the zeolitic framework. This is in agreement with pyridine adsorption studies in which Bronsted acidity was detected. However, the increased acidity decreased the selectivity in the MPV Reduction of cinnamaldehyde as a significant amount of 1-cinnamyl 2-propyl ether was formed as a byproduct. Hence, Al-free Zr-zeolite beta is a useful chemoselective catalyst for the MPV Reduction of α,βα,β-unsaturated aldehydes.
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zirconia catalysts in meerwein ponndorf verley Reduction of citral
Catalysis Today, 2004Co-Authors: Stephan Jaenicke, Gaikhuan ChuahAbstract:Abstract Zirconium-containing catalysts were found to be active in the Meerwein-Ponndorf-Verley (MPV) Reduction of citral. Good activity and selectivity to the reduced alcohol, geraniol and nerol, were observed over hydrous zirconia and zirconium 1-propoxide supported on silica. In particular, hydrous zirconia calcined at temperatures below 300 °C was highly active. Hydrous zirconia catalysts modified by NaOH, NH4F, PO43− and SO42− had lower activity. Surface hydroxyl groups are postulated to be involved in ligand exchange with the reductant, 2-propanol. Zr-zeolite beta showed high activity, but poorer selectivity than the other two samples, due to subsequent dehydration of the product formed. For all catalysts, the trans-isomer of citral was preferentially reduced over the cis-isomer.
Gaik-khuan Chuah - One of the best experts on this subject based on the ideXlab platform.
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Post-synthesized zirconium-containing Beta zeolite in Meerwein–Ponndorf–Verley Reduction: Pros and cons
Applied Catalysis A: General, 2015Co-Authors: Jie Wang, Kazu Okumura, Stephan Jaenicke, Gaik-khuan ChuahAbstract:Abstract Zr-Beta zeolite was prepared by a two-step post-synthesis method involving dealumination of Al-Beta followed by wet impregnation with Zr(NO3)4. Compared with Zr-Beta formed under fluoride-mediated hydrothermal conditions, the post-synthesized samples had smaller particle size and stronger Lewis acidity. The materials were tested as catalysts for Meerwein–Ponndorf–Verley Reduction. In the Reduction of 4-tert-butylcyclohexanone, it exhibited the same excellent stereoselectivity toward cis-4-tert-butylcyclohexanol (>99%) as the HF-synthesized Zr-Beta, but had a lower TOF. Because of the higher density of zirconium sites and the nanosized crystallites, it was a more effective catalyst for the MPV Reduction of 1,4-cyclohexanedione, bulky aldehydes and aromatic ketones. However, it is more susceptible to poisoning by water adsorption because of its hydrophilic nature. The easily scalable synthesis method allows a faster preparation of metal-substituted Lewis acid zeolites, although differences in textural and chemical properties should be taken into consideration when the material is applied as a catalyst.
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Zirconium–Beta zeolite as a robust catalyst for the transformation of levulinic acid to γ-valerolactone via Meerwein–Ponndorf–Verley Reduction
RSC Adv., 2014Co-Authors: Jie Wang, Stephan Jaenicke, Gaik-khuan ChuahAbstract:Zr–Beta zeolite is a robust and active catalyst for the Meerwein–Ponndorf–Verley Reduction of levulinic acid to γ-valerolactone, a versatile intermediate for bio-fuels and chemicals. In a batch reactor, γ-valerolactone was formed with a selectivity of >96%. In a continuous flow reactor, >99% yield of γ-valerolactone was obtained with a steady space-time-yield of 0.46 molGVLgZr−1 h−1 within 87 h, on a par with that of noble metal based catalysts. The high activity of this catalyst was attributed to the presence of Lewis acidic sites with moderate strength. Due to the relatively few basic sites, it is not poisoned by the acidic reactant. Its robustness in liquid and gas phase reactants coupled with good thermal stability makes Zr–Beta a green regenerable catalyst that can be used directly on levulinic acid without the need for derivatization.
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Stereoselective cascade hydrogenation of 4-tert-butylphenol and p-cresol over Zr-zeolite beta-supported rhodium
Journal of Catalysis, 2007Co-Authors: Yuntong Nie, Stephan Jaenicke, Herman Van Bekkum, Gaik-khuan ChuahAbstract:Abstract The hydrogenation of 4- tert -butylphenol and p -cresol was investigated over Zr-beta-supported rhodium catalysts. By designing a suitable bifunctional catalyst, the intermediate, 4-alkylcyclohexanone, formed by metal-catalyzed hydrogenation of 4-alkylphenol, could be reduced via the highly stereoselective Meerwein–Ponndorf–Verley Reduction over zirconium Lewis acid sites. Thus, in the presence of 2-propanol as solvent and MPV reductant, a high stereoselectivity to cis -4-alkylcyclohexanol was observed. Over 0.5% Rh/Zr-beta, 4- tert -butylphenol, and p -cresol were hydrogenated to the cis -alcohols with 95 and 89% stereoselectivity, respectively. A higher metal loading or the use of solvents such as hexane or tert -butanol led to a lower stereoselectivity, as metal-catalyzed hydrogenation predominated. Similarly, the cis : trans alcohol ratio was lower for rhodium supported on zirconia or Al-beta. Compared with rhodium, palladium was less active in the hydrogenation of the 4-alkylphenols, requiring a higher hydrogen pressure and temperature. A two-step cascade reaction mechanism is proposed for the conversion of 4-alkylphenols to cis -4-alkylcyclohexanols.
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Selective Meerwein–Ponndorf–Verley Reduction of α,βα,β-unsaturated aldehydes over Zr-zeolite beta
Journal of Catalysis, 2006Co-Authors: Yongzhong Zhu, Gaik-khuan Chuah, Stephan JaenickeAbstract:Zr-zeolite beta with Si/Zr ratio of 75–200, as well as zeolite beta with both Zr (Si/Zr ratio of 100) and Al (Si/Al ratios of 100 and 25), were synthesized in a seeded synthesis using HF as the mineralizer. The Al-free Zr-zeolite beta was found to catalyse the MPV Reduction of α,βα,β-unsaturated aldehydes to the corresponding alcohols with high selectivity. In the Reduction of cinnamaldehyde to cinnamyl alcohol, TONs of 55–77 mol mol−1Zr h−1 were obtained with selectivity >98%>98%. Zr-zeolite beta maintained good activity and selectivity in the presence of water and benzoic acid. Reuse of the catalyst by washing with 2-propanol or recalcination led to recovery of activity. For the Al-containing Zr-zeolite beta, 27Al NMR spectra showed that Al was incorporated into the zeolitic framework. This is in agreement with pyridine adsorption studies in which Bronsted acidity was detected. However, the increased acidity decreased the selectivity in the MPV Reduction of cinnamaldehyde as a significant amount of 1-cinnamyl 2-propyl ether was formed as a byproduct. Hence, Al-free Zr-zeolite beta is a useful chemoselective catalyst for the MPV Reduction of α,βα,β-unsaturated aldehydes.
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Supported zirconium propoxide—a versatile heterogeneous catalyst for the Meerwein–Ponndorf–Verley Reduction
Journal of Catalysis, 2003Co-Authors: Yongzhong Zhu, Stephan Jaenicke, Gaik-khuan ChuahAbstract:Grafting of zirconium 1-propoxide on SBA-15 resulted in highly active catalysts for the MPV Reduction. The activity increased with zirconium loading up to a monolayer coverage. In most cases, there were no side products other than the desired alcohol. Electron-donating groups adjacent to the carbonyl group in the substrate facilitate the reaction. The grafted zirconium catalysts did not lose their activity in the presence of moisture or on exposure to ambient atmosphere, making them easy to handle and reuse. No leaching of the grafted zirconium 1-propoxide into the reaction mixture was observed. The addition of pyridine and water to the reaction medium had only a small effect on its activity while benzoic acid led to severe deactivation. The deactivation is attributed to strong adsorption of benzoic acid at the Zr metal centres which could be reversed on removal of the poison. Aluminum 2-propoxide grafted on SBA-15 resulted in a less active catalyst than the zirconium catalysts. The good resistance to hydrolysis of the zirconium catalysts makes them superior to the aluminum 2-propoxide catalysts.
H. Van Bekkum - One of the best experts on this subject based on the ideXlab platform.
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Zeolite Beta: The Relationship Between Calcination Procedure, Aluminum Configuration and Lewis Acidity
Journal of Catalysis, 1998Co-Authors: P.j. Kunkeler, B.j. Zuurdeeg, J.c. Van Der Waal, J. A. Van Bokhoven, D.c. Koningsberger, H. Van BekkumAbstract:Abstract Zeolite Beta was calcined under a variety of carefully controlled conditions to study the influence of (hydro)thermal treatments on the catalytic activity of zeolite Beta in the Lewis acid-catalyzed Meerwein–Ponndorf–Verley Reduction of ketones. The activity of (H)Beta can be increased by several orders of magnitude by mild steaming. The catalytic activity of the materials following reactivation can be diminished again by adsorption of ammonia followed by an induction period. For these changes, an explanation is offered in terms of Lewis acidic framework aluminum atoms which undergo a change of configuration depending on the ligands present, rather than becoming extraframework aluminum. FTIR, 29 Si, and 27 Al MAS NMR spectroscopy were applied to investigate the changes induced by the (hydro)thermal procedures.
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Zeolite Titanium Beta: A Selective Catalyst for the Gas-Phase Meerwein–Ponndorf–Verley, and Oppenauer Reactions☆
Journal of Catalysis, 1998Co-Authors: J.c. Van Der Waal, P.j. Kunkeler, K. Tan, H. Van BekkumAbstract:Aluminium-free zeolite titanium beta was tested in the Meerwein–Ponndorf–Verley Reduction of 4-methylcyclohexanone with various secondary and primary alcohols as hydrogen donors, using a fixed-bed continuous-flow gas-phase reactor. A high selectivity towards the thermodynamically unfavourablecis-4-methylcyclohexanol was observed, which is ascribed to transition-state selectivity in the straight channels of zeolite beta. However, in the gas-phase, the selectivity to thecis-alcohol is significantly lower than in the liquid-phase when using 2-propanol as the hydrogen donor. Based on kinetic and adsorption experiments, it is concluded that the concentration of alcohol reductant in the zeolite is an important parameter in determining selectivity. More hydrophobic alcohols give rise to an increased selectivity to thecis-alcohol product. From the sorption experiments it was concluded that this is due to a higher internal concentration of the alcohol reductant in the hydrophobic titanium beta zeolite. The observed selectivities and activities are consistent with a mechanism in which this alcohol is not only the hydrogen donor but is also required to remove thecis-alcohol product formed from the catalytic site by alcoholysis, before consecutive reactions can take place.
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Beta–type zeolites as selective and regenerable catalysts in the Meerwein–Ponndorf–Verley Reduction of carbonyl compounds
Topics in Catalysis, 1997Co-Authors: J.c. Van Der Waal, E.j. Creyghton, P.j. Kunkeler, K. Tan, H. Van BekkumAbstract:Zeolite Beta, in the Al–form as well as in the Al–free, Ti–containing form, appears to be a selective and regenerable catalyst in the Meerwein–Ponndorf–Verley and Oppenauer (MPVO) reactions. In the liquid–phase MPV Reduction of 4–tert–butylcyclohexanone with secondary alcohols, both catalysts display a high stereoselectivity to cis–4–tert–butylcyclohexanol, the isomer of industrial relevance. This stereoselectivity can be explained by considering the two transition states inside the pores of zeolite Beta. By using (S)–2–butanol as the reductant enantioselective Reduction of phenylacetone was observed. 4–methylcyclohexanone was studied as the substrate in the gas–phase MPV Reduction. Catalyst deactivation is much more pronounced with the acidic Al–Beta catalyst than with the non–acidic Ti–Beta.
J.c. Van Der Waal - One of the best experts on this subject based on the ideXlab platform.
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Zeolite Beta: The Relationship Between Calcination Procedure, Aluminum Configuration and Lewis Acidity
Journal of Catalysis, 1998Co-Authors: P.j. Kunkeler, B.j. Zuurdeeg, J.c. Van Der Waal, J. A. Van Bokhoven, D.c. Koningsberger, H. Van BekkumAbstract:Abstract Zeolite Beta was calcined under a variety of carefully controlled conditions to study the influence of (hydro)thermal treatments on the catalytic activity of zeolite Beta in the Lewis acid-catalyzed Meerwein–Ponndorf–Verley Reduction of ketones. The activity of (H)Beta can be increased by several orders of magnitude by mild steaming. The catalytic activity of the materials following reactivation can be diminished again by adsorption of ammonia followed by an induction period. For these changes, an explanation is offered in terms of Lewis acidic framework aluminum atoms which undergo a change of configuration depending on the ligands present, rather than becoming extraframework aluminum. FTIR, 29 Si, and 27 Al MAS NMR spectroscopy were applied to investigate the changes induced by the (hydro)thermal procedures.
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Zeolite Titanium Beta: A Selective Catalyst for the Gas-Phase Meerwein–Ponndorf–Verley, and Oppenauer Reactions☆
Journal of Catalysis, 1998Co-Authors: J.c. Van Der Waal, P.j. Kunkeler, K. Tan, H. Van BekkumAbstract:Aluminium-free zeolite titanium beta was tested in the Meerwein–Ponndorf–Verley Reduction of 4-methylcyclohexanone with various secondary and primary alcohols as hydrogen donors, using a fixed-bed continuous-flow gas-phase reactor. A high selectivity towards the thermodynamically unfavourablecis-4-methylcyclohexanol was observed, which is ascribed to transition-state selectivity in the straight channels of zeolite beta. However, in the gas-phase, the selectivity to thecis-alcohol is significantly lower than in the liquid-phase when using 2-propanol as the hydrogen donor. Based on kinetic and adsorption experiments, it is concluded that the concentration of alcohol reductant in the zeolite is an important parameter in determining selectivity. More hydrophobic alcohols give rise to an increased selectivity to thecis-alcohol product. From the sorption experiments it was concluded that this is due to a higher internal concentration of the alcohol reductant in the hydrophobic titanium beta zeolite. The observed selectivities and activities are consistent with a mechanism in which this alcohol is not only the hydrogen donor but is also required to remove thecis-alcohol product formed from the catalytic site by alcoholysis, before consecutive reactions can take place.
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Beta–type zeolites as selective and regenerable catalysts in the Meerwein–Ponndorf–Verley Reduction of carbonyl compounds
Topics in Catalysis, 1997Co-Authors: J.c. Van Der Waal, E.j. Creyghton, P.j. Kunkeler, K. Tan, H. Van BekkumAbstract:Zeolite Beta, in the Al–form as well as in the Al–free, Ti–containing form, appears to be a selective and regenerable catalyst in the Meerwein–Ponndorf–Verley and Oppenauer (MPVO) reactions. In the liquid–phase MPV Reduction of 4–tert–butylcyclohexanone with secondary alcohols, both catalysts display a high stereoselectivity to cis–4–tert–butylcyclohexanol, the isomer of industrial relevance. This stereoselectivity can be explained by considering the two transition states inside the pores of zeolite Beta. By using (S)–2–butanol as the reductant enantioselective Reduction of phenylacetone was observed. 4–methylcyclohexanone was studied as the substrate in the gas–phase MPV Reduction. Catalyst deactivation is much more pronounced with the acidic Al–Beta catalyst than with the non–acidic Ti–Beta.
Yongzhong Zhu - One of the best experts on this subject based on the ideXlab platform.
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Selective Meerwein–Ponndorf–Verley Reduction of α,βα,β-unsaturated aldehydes over Zr-zeolite beta
Journal of Catalysis, 2006Co-Authors: Yongzhong Zhu, Gaik-khuan Chuah, Stephan JaenickeAbstract:Zr-zeolite beta with Si/Zr ratio of 75–200, as well as zeolite beta with both Zr (Si/Zr ratio of 100) and Al (Si/Al ratios of 100 and 25), were synthesized in a seeded synthesis using HF as the mineralizer. The Al-free Zr-zeolite beta was found to catalyse the MPV Reduction of α,βα,β-unsaturated aldehydes to the corresponding alcohols with high selectivity. In the Reduction of cinnamaldehyde to cinnamyl alcohol, TONs of 55–77 mol mol−1Zr h−1 were obtained with selectivity >98%>98%. Zr-zeolite beta maintained good activity and selectivity in the presence of water and benzoic acid. Reuse of the catalyst by washing with 2-propanol or recalcination led to recovery of activity. For the Al-containing Zr-zeolite beta, 27Al NMR spectra showed that Al was incorporated into the zeolitic framework. This is in agreement with pyridine adsorption studies in which Bronsted acidity was detected. However, the increased acidity decreased the selectivity in the MPV Reduction of cinnamaldehyde as a significant amount of 1-cinnamyl 2-propyl ether was formed as a byproduct. Hence, Al-free Zr-zeolite beta is a useful chemoselective catalyst for the MPV Reduction of α,βα,β-unsaturated aldehydes.
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Supported zirconium propoxide—a versatile heterogeneous catalyst for the Meerwein–Ponndorf–Verley Reduction
Journal of Catalysis, 2003Co-Authors: Yongzhong Zhu, Stephan Jaenicke, Gaik-khuan ChuahAbstract:Grafting of zirconium 1-propoxide on SBA-15 resulted in highly active catalysts for the MPV Reduction. The activity increased with zirconium loading up to a monolayer coverage. In most cases, there were no side products other than the desired alcohol. Electron-donating groups adjacent to the carbonyl group in the substrate facilitate the reaction. The grafted zirconium catalysts did not lose their activity in the presence of moisture or on exposure to ambient atmosphere, making them easy to handle and reuse. No leaching of the grafted zirconium 1-propoxide into the reaction mixture was observed. The addition of pyridine and water to the reaction medium had only a small effect on its activity while benzoic acid led to severe deactivation. The deactivation is attributed to strong adsorption of benzoic acid at the Zr metal centres which could be reversed on removal of the poison. Aluminum 2-propoxide grafted on SBA-15 resulted in a less active catalyst than the zirconium catalysts. The good resistance to hydrolysis of the zirconium catalysts makes them superior to the aluminum 2-propoxide catalysts.