Intramolecular selective hydrogenation of cinnamaldehyde over CeO2–ZrO2-supported Pt catalysts

Selective liquid phase hydrogenation of cinnamaldehyde is reported, for the first time, over CeO₂, ZrO₂, and CeO₂–ZrO₂-supported Pt catalysts. Cinnamyl alcohol is the selective product. These catalysts are highly active and selective even at 25 °C and found to be superior to most of the hitherto known supported Pt catalysts. Alkali addition (NaOH) has enhanced the performance of these catalysts. At an optimized reaction condition, 95.8% conversion of cinnamaldehyde and 93.4% selectivity of cinnamyl alcohol have been obtained. Acidity of the support (due to the presence of ZrO₂ component) and higher electron density at Pt (due to CeO₂ component) are attributed to be responsible for the superior catalytic activity of Pt supported on CeO₂–ZrO₂ composite material.     

Fullerene‐based ruthenium catalysts in cinnamaldehyde hydrogenation

Ruthenium on fullerenes and ruthenium and palladium on activated carbon were compared for their catalytic activity and selectivity in cinnamaldehyde hydrogenation. The fullerene support had a marked effect on the selectivity, even though the fullerenes themselves showed no catalytic activity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Influence factors on activity of Ru–Zn catalysts in selective hydrogenation of benzene

Selective hydrogenation of benzene is an atom economic green route to produce cyclohexene. The control of Zn species is the key to the catalytic performance of Ru–Zn catalysts. The influences of ZnO crystals on selective hydrogenation of benzene were explored. A series of Ru–Zn catalysts with different Zn contents and ZnO morphologies were prepared by changing the amount of NaOH in the co-precipitation process. The catalysts were characterized by N_2 physisorption, X-ray powder diffraction(XRD), inductively coupled plasma optical emission spectrometer(ICP-OES), scanning electron microscope(SEM), temperature-programmed reduction(H_2-TPR)and Malvern laser particle size analyzer. It is found that with increasing the amount of NaOH, the Zn content first increased then decreased, and the ZnO crystals changed from relatively thicker pyramidal-shaped crystals to slimmer needle-shaped crystals. The catalyst had the highest Zn content(22.1%) and strongest interaction between ZnO crystals and Ru particles at pH 10.6 of the solution after reduction. As a result, it had the lowest activity. The activity of Ru–Zn catalysts is affected by both the Zn content and the interaction between ZnO crystals and Ru particles. The effect of reduction time was also investigated. Prolonging the reduction time caused no significant growth of ZnO crystals but the aggregation of catalyst particles and growth of Ru nanocrystals, thus resulting in the decrease of catalytic activity.     

EXAFS characterization of bimetallic Pt–Pd/SiO2–Al2O3 catalysts for hydrogenation of aromatics in diesel fuel

Bimetallic Pt–Pd/SiO₂–Al₂O₃ catalysts exhibited much higher activities in aromatic hydrogenation of distillates than monometallic Pt/SiO₂–Al₂O₃ and Pd/SiO₂–Al₂O₃ catalysts. The studies of extended X‐ray absorption fine structure (EXAFS) indicated that there was an interaction between Pt and Pd in the Pt–Pd/ SiO₂–Al₂O₃ catalyst. Furthermore, from the EXAFS, it was assumed that the active metal particle on the Pt–Pd/SiO₂–Al₂O₃ catalysts is composed of the “Pd dispersed on Pt particle” structure. Regarding both the activities of aromatic hydrogenation and the EXAFS results, it was concluded that the Pd species dispersed on Pt particles were responsible for the high activity of the bimetallic Pt–Pd/SiO₂–Al₂O₃ catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Tuning product selectivity of CO2 hydrogenation by OH groups on Pt/γ-AlOOH and Pt/γ-Al2O3 catalysts

Herein, we explore how OH groups on Pt/γ-AlOOH and Pt/γ-Al₂O₃ catalysts affect CO₂ hydrogenation with H₂ at temperatures from 250°C to 400°C. OH groups are abundant on γ-AlOOH, but rare at Pt-(γ-AlOOH) interface which is the most favorable site for CO₂ conversion on Pt/γ-AlOOH. This makes CO₂ hydrogenation on Pt/γ-AlOOH form CO weakly bonding to γ-AlOOH, which prefers to desorption from Pt/γ-AlOOH rather than further conversion, thus enhancing CO production on Pt/γ-AlOOH. Different from Pt/γ-AlOOH, OH groups are abundant at Pt-(γ-Al₂O₃) interface which is the most favorable site for CO₂ conversion on Pt/γ-Al₂O₃. This promotes CO₂ hydrogenation on Pt/γ-Al₂O₃ to form CO strongly bonding to Pt, which prefers to further hydrogenation to CH₄, and thereby increases CH₄ selectivity on Pt/γ-Al₂O₃. Therefore, the OH groups at metal-support interface are crucial factor influencing product distribution, and must be considered seriously when fabricating catalysts.     

CuO–CeO2 mixed oxide catalysts for the selective oxidation of carbon monoxide in excess hydrogen

A series of mixed oxide CuO–CeO₂ catalysts were prepared by coprecipitation and tested for the selective oxidation of carbon monoxide in the presence of excess hydrogen. These catalysts were found to be very active and exceptionally selective for this reaction and exhibited a good resistance towards CO₂ and H₂O. The catalytic performance of these non-noble metal containing catalysts is compared with that of other selective CO oxidation catalysts reported in literature.     

Acid function of Al‐MCM‐41 supported platinum catalysts in hydrogenation of benzene, toluene o‐xylene

A series of Al‐MCM‐41 mesoporous materials with different Si/Al ratios are synthesized. The acidities of catalysts are measured by the temperature‐programmed desorption of ammonia (NH₃‐TPD) and IR spectra of pyridine. Their catalytic activities for hydrogenation of benzene, toluene and o‐xylene are investigated on a pulse reactor system. NH₃‐TPD and IR results show that only weak and medium acid sites could be observed on the catalysts, and the number of total acid sites decreases obviously with the increase of the Si/Al ratio whereas the medium acid sites are somewhat constant. The introduction of platinum onto Al‐MCM‐41 material decreases the total acid number by a small amount. The hydrogenation activities of the 1% Pt/HAl‐MCM‐41 catalysts are found to correspond well with the ratio of medium acid sites to total acid sites in the employed catalysts. It is proposed that, in addition to metal sites, the acid sites in the metal–acid interfacial regions are also the active sites for hydrogenation and the medium acid sites play important roles in the reaction. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of loading method on selective hydrogenation of chloronitrobenzenes over amorphous Ni–B/CNTs catalysts

Carbon nanotubes (CNTs)-supported amorphous Ni–B catalysts were prepared by selectively depositing Ni–B particles inside or outside the CNTs (Ni–B-in/CNTs or Ni–B-out/CNTs). Hydrogenation of chloronitrobenzenes was carried out to test how the Ni–B particle-loading method over the CNTs affected the catalytic performance. Compared with the Ni–B-out/CNTs, the Ni–B-in/CNTs, because of the nanospace limitation inside the CNTs, restricted the size and aggregative behavior of the Ni–B particles better, and formed an amorphous Ni–B alloy with high thermal stability. The Ni–B-in/CNTs exhibited a much higher catalytic activity for hydrogenation of chloronitrobenzenes than the Ni–B-out/CNTs.     

Pd/polyaniline as the catalysts for 2‐ethylanthraquinone hydrogenation. The effect of palladium dispersion

By doping of polyaniline (PANI) in PdCl₂ aqueous and ethanol solutions the catalysts containing crystalline and colloidal Pd particles of different sizes were prepared. The size of palladium particles present in Pd/PANI catalysts (characterised by SEM and XRD methods) influenced the course of 2‐ethylanthraquinone (eAQ) hydrogenation, a key step in the industrial production of H₂O₂. The presence of large palladium particles promotes reactions leading to the formation of the so‐termed “degradation products” not capable of hydrogen peroxide formation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Structure/activity correlation for unpromoted and CeO2‐promoted MnO2/SiO2 catalysts

The goal of this study was to understand the structure–activity relationship for unpromoted and ceria‐promoted MnO_x/SiO₂ catalysts used in CO oxidation. SiO₂ and CeO₂‐promoted SiO₂ (20% CeO₂) were used as supports to prepare MnO_x/SiO₂ catalysts with various manganese (Mn) loadings. X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy (XPS) data indicated a higher Mn dispersion on ceria‐promoted than on unpromoted MnO_x/SiO₂ catalysts. Analysis of the XRD patterns and Mn_2p XPS spectra indicated that Mn was present as MnO₂ on MnO_x/SiO₂ with low Mn loadings and ceria‐promoted MnO_x/SiO₂ catalysts and as mixed MnO₂/Mn₂O₃ on MnO_x/SiO₂ catalysts with high Mn loadings. Kinetic data obtained for CO oxidation on unpromoted and ceria‐promoted MnO_x/SiO₂ catalysts are presented and interpreted in correlation with the catalyst surface and bulk structure. A synergistic catalytic effect was observed in the case of the ceria‐promoted MnO_x/SiO₂ catalysts. Post‐reaction XRD and XPS analysis of catalysts indicated that the presence of ceria precludes formation of the less catalytically active Mn₃O₄ species from MnO₂ deposited initially on the SiO₂ support. This revised version was published online in July 2006 with corrections to the Cover Date.     

Platinum/3,3´-thiodipropionic acid nanoparticles as recyclable catalysts for the selective hydrogenation of trans-cinnamaldehyde

Platinum nanoparticles as spherical aggregates were prepared by the reduction of a Pt(II) salt with hydrazine using 3,3´-thiodipropionic acid as a protective agent, and characterized by IR, XRF, XRD, and SEM where agglomerates have been visualized. The average crystallite size was 6 nm. For the first time such nanoparticles were evaluated as catalysts in the hydrogenation of unsaturated aldehydes. Hydrogenation of trans-cinnamaldehyde yielded cinnamyl alcohol with a selectivity of up to 83% at complete substrate conversion. At 30 °C, the catalyst could be recycled and reused for three runs with only slight losses in activity and selectivity.     

The catalytic performance of Ti-PILC supported CrOx–CeO2 catalysts for n-butylamine oxidation

Journal of Porous Materials - A series of titanium pillared clays (Ti-PILC) materials are synthesized by different preparation conditions and the influence of the texture/structure nature of...     

Catalytic performance of advanced titanosilicate selective oxidation catalysts – a review

This review article aims to cover the state-of-the-art of titanosilicate catalysts for selective oxidations developed within past seven years. Many elaborated materials (e.g., layered and pillared titanosilicates, hierarchical composite materials, and others) have been prepared and thoroughly characterized; however, their catalytic properties have been usually investigated only using a single or few model substrates and compared with a benchmarking material. The main goal of this article is to summarize the novel catalysts and compare their catalytic performance with each other. The comparison is focused on epoxidation. In addition, phenol hydroxylation and sulphide oxidation are briefly covered.     

Performance of Pd–Ag/Al2O3 catalysts prepared by the selective deposition of Ag onto Pd in acetylene hydrogenation

The performance of Ag-promoted Pd/Al₂O₃ catalysts, which were prepared by the selective deposition of Ag onto Pd using a surface redox (SR) method, during acetylene hydrogenation was compared with that of catalysts prepared by impregnation. The Pd surface was more effectively modified with Ag added by SR, even when small amounts of Ag were added. The catalyst prepared by SR showed a higher ethylene selectivity than the one prepared by impregnation, because SR allowed both the preferential deposition of Ag on the low-coordination sites of Pd and a greater electronic modification of Pd by Ag.     

The function of zeolite on Pt autoreduction and dispersion in Pt/L and Pt/β catalysts

TPR, CO-FTIR and¹²⁹Xe NMR spectroscopic techniques were used to measure the distribution of platinum species after the calcination of Pt/L and Pt/ zeolites. Autoreduction which occurred in Pt/ zeolite was avoided in the channel of L zeolite. Pt particles dispersed well and exhibited excellent reactivity for the aromatization ofn-hexane in L zeolite.     

Influence of the crystalline structure of ZrO2 on the metallic properties of Pt in Pt/WO3–ZrO2 catalysts

The influence of the crystalline structure of ZrO₂ on the metallic properties of Pt, when supported on WO₃–ZrO₂, was studied. Pt supported on tetragonal zirconia loses its metallic properties while when supported on monoclinic zirconia it presents good metallic activities. WO₂,^2- deposited on amorphous Zr(OH)₄ before calcination generates an active material for n‐butane isomerization. The larger the fraction of the tetragonal phase of zirconia in this material, the higher the isomerization activity and the lower the metallic activity of Pt. This revised version was published online in July 2006 with corrections to the Cover Date.     

AlCl3-promoted MCM-41-supported platinum catalysts with high activity and sulfur-tolerance for tetralin hydrogenation: Effect of Pt–Al interaction

AlCl₃-promoted MCM-41-supported platinum catalysts with different Al–Pt interaction sequences were prepared for tetralin hydrogenation under sulfur-containing condition. Platinum dispersion and acidity of the catalysts were improved by the introduction of aluminum. The aluminum-containing catalysts have similar acidity. Al–Pt interaction leads to the formation of electron-deficient platinum (Pt^δ +). A great improvement in sulfur-tolerance was observed on the catalyst that aluminum is grafted after the supporting of platinum.     

Highly selective hydrogenation of phenol and derivatives over Pd catalysts supported on SiO2 and γ-Al2O3 in aqueous media

Pd/Al₂O₃ and Pd/SiO₂ catalysts containing Pd nanoparticles in the size range of 3–13 nm were prepared and investigated in direct selective hydrogenation of phenol to cyclohexanone. Catalysts with 3 nm Pd nanoparticles present highly active and promoted the selective formation of cyclohexanone under atmospheric pressure of hydrogen in aqueous media without additives. Conversion of 99% and a selectivity higher than 99% were achieved within 3 h at 333 K. The generality of Pd/Al₂O₃ catalyst with 3 nm Pd nanoparticles for this reaction was demonstrated by selective hydrogenation of other hydroxylated aromatic compounds with similar performance.