钾对丙烷脱氢催化剂性能的影响

考察助剂钾对氧化铝和介孔分子筛SBA-15载体体系的丙烷脱氢催化剂性能的影响,XRD、NH₃-TPD和铂分散度表征结果表明,钾对两种体系催化剂的影响完全不同,在氧化铝体系中,钾助剂降低催化剂酸性,提高催化剂性能,而在SBA-15载体体系中,钾的引入使催化剂中铂的分散度大大降低,从而使催化剂活性降低,不利于反应。     

Enhanced synergy between Cu0 and Cu+ on nickel doped copper catalyst for gaseous acetic acid hydrogenation

As the substitution of common noble catalysts in the hydrogenation of carboxylic acid, a highly effective Cu-Ni/SiO₂ catalyst was prepared by a novel stepwise ammonia evaporation method. Its performance in the gas-phase hydrogenation of acetic acid was further examined. With the introduction of Ni dopant, more stable Cu^δ+ sites, which can adsorb more acetic acid, were formed due to the electron transfer from Cu to Ni. This makes more Cu⁰ sites available for hydrogen adsorption, which was suggested as the rate-determining step in acetic acid hydrogenation. A conversion of 99.6% was successfully achieved on this new Cu/SiO₂-0.5Ni catalyst, accompanied by the ethanol selectivity of 90%. The incorporation of nickel between copper nanoparticles enhances the synergistic effect between Cu⁰ and Cu⁺. It also helps mitigate the aggregation of copper nanoparticles due to the Ostwald ripening effect induced by acetic acid and enhance the stability of copper catalyst in the conversion of carboxylic acid.     

Development of anode catalysts for a direct ethanol fuel cell

Ethanol electrooxidation was investigated at platinum based electrodes: Pt, Pt—Sn, Pt—Re dispersed on a high surface area carbon powder. The atomic composition of the bimetallic catalyst was varied and the best results were obtained with an atomic ratio Pt:X close to 100:20. The electrocatalytic activity of Pt, PtSn and PtRe was compared using cyclic voltammetry and long-term electrolyses at constant potential. Under voltammetric conditions and in a single direct ethanol fuel cell, PtSn was the most active catalyst. During electrolysis ethanol was oxidized to acetaldehyde (AAL), acetic acid (AA) and carbon dioxide. On PtSn/C and PtRe/C, the ratio AA/AAL was found to be always lower than unity. Otherwise, PtSn electrocatalysts were the most selective towards the production of CO₂ compared to Pt and PtRe electrodes.     

Effect of pre-treatment approach of a carbon support on activity of PtSn/C electrocatalysts for direct ethanol fuel cells

Vulcan XC-72R carbon was pretreated using acid and thermal activation methods, and the carbons obtained were used as supports for a PtSn/C catalyst synthesized by a successive reduction process. Surface characteristics of the supports, including BET surface area, pH_PZC and functional group, were analyzed using physical N₂ adsorption, mass titration, acid–base titration, and Fourier transform infrared (FTIR) spectrometer technique, respectively. The prepared PtSn/C catalysts were characterized by X-ray diffractometer (XRD), energy dispersive X-ray spectrometer (EDX), inductively coupled plasma–atomic emission spectrometry (ICP–AES), and transmission electron microscope (TEM) techniques, and then were examined for their behavior under ethanol oxidation as well as for their performance in a direct ethanol fuel cell (DEFC). The results showed that pretreatment by HNO₃ produced various oxygenated functional groups on the support surface and increased its acidic property. The strong acidity of the acid-treated support led to an unfavorable condition for the Pt reduction reaction and resulted in low Pt content but high Pt:Sn ratio in the PtSn/C catalyst. On the other hand, thermal activation increased the base functional groups on the carbon surface, which enhanced reduction of Pt precursor, and consequently, provided a small average metal particle size of 2.2 nm. The results from cyclic voltammetry, chronoamperometry and cell performance testing confirmed that the catalytic activity for ethanol oxidation and the performance in the direct ethanol fuel cell of the heat-treated carbon-supported PtSn catalyst was superior to the fresh PtSn/C catalyst and the acid-treated carbon-supported PtSn catalyst.     

Effect of thermal pretreatment on the surface structure of PtSn/SiO<Subscript>2</Subscript> catalyst and its performance in acetic acid hydrogenation

The effect of thermal pretreatment on the active sites and catalytic performances of PtSn/SiO₂ catalyst in acetic acid (AcOH) hydrogenation was investigated in this article. The catalysts were characterized by N₂ physical adsorption, X-ray diffraction, transmission electron microscopy, pyridine Fourier-transform infrared spectra, and H₂-O₂ titration on its physicochemical properties. The results showed that Pt species were formed primarily in crystalline structure and no PtSn _x alloy was observed. Meanwhile, with the increment of thermal pretreatment temperature, Pt dispersion showed a decreasing trend due to the aggregation of Pt particles. Simultaneously, the amount of Lewis acid sites was remarkably influenced by such thermal pretreatment owning to the consequent physicochemical property variation of Sn species. Interestingly, the catalytic activity showed the similar variation trend with that of Lewis acid sites, confirming the important roles of Lewis acid sites in AcOH hydrogenation. Moreover, a balancing effect between exposed Pt and Lewis acid sites was obtained, resulting in the superior catalytic performance in AcOH hydrogenation.

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Ni2P/SiO2催化剂制备及其乙酸加氢制乙醇催化性能评价

通过等体积浸渍和N₂气流中热处理过程制备了系列氧化硅负载过渡金属磷化物催化剂,经乙酸加氢制乙醇反应实验和动力学分析评价催化剂性能。研究结果表明,随着反应温度从280℃升高到340℃,乙酸转化率和乙醇选择性均逐渐提高。随着催化剂制备的P/Ni摩尔比从2：1增大到4：1,催化剂活性和乙醇选择性均先增大后减小,P/Ni摩尔比为3：1催化剂性能较佳。250℃热处理制备催化剂的催化性能优于200℃及300℃。Ni₂P/SiO₂催化剂活性和乙醇选择性均高于Co₂P/SiO₂催化剂。用次磷酸钠作为磷补充源制备催化剂的性能优于次磷酸钾。采用较佳条件下制备的Ni₂P/SiO₂催化剂,在温度340℃、压力2.0 MPa、氢酸进料量比10：1、质量空速0.4 h^-1条件下进行乙酸加氢反应,乙酸转化率为100%,乙醇选择性达到74.56%,并且适当升高反应温度会进一步提高乙醇选择性。     

Ni/Al_2O_3-M_xO_y催化剂催化松香加氢的催化性能及产物组成

研究了Ni/Al2O3-MxOy,催化剂催化松香氢化反应的催化性能,结果表明Ni/Al2O3-MxOy催化剂催化松香氢化具有较好的催化性能,枞酸转化率可达98%以上,氢化产物达到国家普通氢化松香(特级)标准.产物主要组分与Pd/C催化剂催化所得的氢化产物基本相同.     

Influence of Preparation Modes on Pt–Ni/CNTs Catalysts Used in the Selective Hydrogenation of Cinnamaldehyde to Hydrocinnamaldehyde

Pt–Ni/CNTs catalysts are prepared by different impregnation techniques and different reduction methods (H₂, HCHO, and KBH₄) for the selective hydrogenation of cinnamaldehyde (CMA) to hydrocinnamaldehyde (HCMA) and investigated by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and temperature programmed reduction (H₂-TPR) techniques. The results show that the catalytic selectivity and activity of the Pt–Ni/CNTs catalysts would significantly be improved by using KBH₄ as a reducing agent, due to the electronic synergetic effect of Pt–Ni–B, and 96% for conversion of CMA and 88% for selectivity of HCMA are obtained over Pt–Ni/CNTs catalyst reduced by KBH₄. Furthermore, the hydrogenation rate of CMA and selectivity of CMA to HCMA over Pt–Ni/CNTs catalyst are significantly improved in the presence of trace base or acid promoters again. The best result (92% for conversion of CMA and 96% for selectivity of HCMA) is obtained when NaOAc is used as base promoter.     

Effect of Metal Type on Partial Hydrogenation of Rapeseed Oil-Derived FAME

Supported SiO₂ catalysts were studied for the partial hydrogenation of rapeseed oil-derived fatty acid methyl esters (FAME) for improving its oxidative stability. The effect of metal type: Pt, Pd, and Ni, on catalytic activity and cis–trans selectivity was investigated. Hydrogenation activity was studied in terms of turn over frequency (TOF) of C18:3, C18:2, C18:1, and C18:0 FAME. The highest TOF of C18:3, C18:2, and C18:1 was found for Pd catalyst. However, C18:0 TOF of Pt is higher than that of the Pd catalyst. The higher in C18:0 TOF can explain the low selectivity towards trans-monounsaturated FAME of the Pt catalyst, which is due to the subsequent hydrogenation of the intermediate trans-monounsaturated to saturated FAME. On the other hand, Ni showed the lowest TOFs when compared with the Pt and Pd catalysts.     

The Promoting Effect of Europium on PtSn/C Catalyst for Ethanol Oxidation

Well‐dispersed PtSnEu/C and PtSn/C catalysts were prepared by the impregnation–reduction method using formic acid as a reductant and characterised by X‐ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersion X‐ray spectroscopy (EDX) and X‐ray photoelectron spectroscopy (XPS). The synthesised catalysts with different atomic ratios of Pt/Sn/Eu have the Pt face centered cubic (fcc) structure and their particle sizes are 3–4 nm. The PtSnEu/C catalyst is composed of many Pt (0), SnO₂, Eu(OH)₃, a small amount of Pt(II) and partly alloyed PtSn, but no metallic Eu. The electrochemical measurements indicate that in comparison with Pt₃Sn₁/C catalyst, the Pt₃Sn₁Eu₁/C catalyst for ethanol oxidation has more negative onset potential, smaller apparent activation energy and lower electrochemical impedance so that it exhibits very high catalytic activity. Its peak current density increases by 135% and 40%, compared with Pt₃Sn₁/C and Pt₁Ru₁/C (JM) catalysts, respectively. This is because the Eu(OH)₃ formed by adding Eu to PtSn/C catalyst can provide the OH group which is in favour of the removal of adsorbed intermediates and ethanol oxidation.     

Effect of alloying degree in PtSn catalyst on the catalytic behavior for ethanol electro-oxidation

Carbon-supported binary PtSn catalysts with varied alloying degree were synthesized in different processes and denoted as PtSn/C-B, PtSn/C-EG and PtSnO₂/C, respectively. X-ray diffraction (XRD) characterizations showed that PtSn/C-B catalyst displayed the highest alloying degree, while PtSnO₂/C catalyst had the lowest one among these samples. X-ray photoelectron spectroscopy (XPS) results revealed that the non-alloyed Sn existed in an oxidized state on the surfaces of these catalysts. By evaluating the electro-catalytic activity and analyzing the final products of ethanol oxidation reaction (EOR) on these catalysts, it was found that PtSnO₂/C catalyst enhanced the products yield of acetic acid products and PtSn/C-B catalyst promoted the entire activity for EOR. It was proposed that non-alloyed SnO₂ species enhanced the bi-functional mechanism, whereas PtSn alloy phase strengthened the electronic effect of PtSn/C catalyst.     

Structure and chemical composition of supported Pt-Sn electrocatalysts for ethanol oxidation

Carbon supported PtSn alloy and PtSnO_x particles with nominal Pt:Sn ratios of 3:1 were prepared by a modified polyol method. High resolution transmission electron microscopy (HRTEM) and X-ray microchemical analysis were used to characterize the composition, size, distribution, and morphology of PtSn particles. The particles are predominantly single nanocrystals with diameters in the order of 2.0-3.0 nm. According to the XRD results, the lattice constant of Pt in the PtSn alloy is dilated due to Sn atoms penetrating into the Pt crystalline lattice. While for PtSnO_x nanoparticles, the lattice constant of Pt only changed a little. HRTEM micrograph of PtSnO_x clearly shows that the change of the spacing of Pt (1 1 1) plane is neglectable, meanwhile, SnO₂ nanoparticles, characterized with the nominal 0.264 nm spacing of SnO₂ (1 0 1) plane, were found in the vicinity of Pt particles. In contrast, the HRTEM micrograph of PtSn alloy shows that the spacing of Pt (1 1 1) plane extends to 0.234 nm from the original 0.226 nm. High resolution energy dispersive X-ray spectroscopy (HR-EDS) analyses show that all investigated particles in the two PtSn catalysts represent uniform Pt/Sn compositions very close to the nominal one. Cyclic voltammograms (CV) in sulfuric acid show that the hydrogen ad/desorption was inhibited on the surface of PtSn alloy compared to that on the surface of the PtSnO_x catalyst. PtSnO_x catalyst showed higher catalytic activity for ethanol electro-oxidation than PtSn alloy from the results of chronoamperometry (CA) analysis and the performance of direct ethanol fuel cells (DEFCs). It is deduced that the unchanged lattice parameter of Pt in the PtSnO_x catalyst is favorable to ethanol adsorption and meanwhile, tin oxide in the vicinity of Pt nanoparticles could offer oxygen species conveniently to remove the CO-like species of ethanolic residues to free Pt active sites.     

Nickel crystallite size and net activity of hydrogenation catalysts

Among supported nickel-based hydrogenation catalysts, the Ni crystallite size apparently plays a secondary role in net hydrogenation activity for undistilled tallow fatty acids and nonselective hydro-genation of oxidized soybean oil. The nickel crystal-lite size measured by the x-ray diffraction profile broadening technique of Scherrer varied between 55 A and 150 A. The commercial catalyst with the small-est nickel crystallite size, in the samples studied, was not the most active for hardening soybean oil, while fatty acid hydrogenation showed a large crystallite catalyst to have the highest activity. Since the percent reduced nickel used in catalytic hydrogenation is not well known if the Ni/NiO ratio is poorly defined, relative activities were then correlated with qualita-tive x-ray diffraction measurements of the Ni/NiO values. Again, there was no trend in activity as a func-tion of Ni/NiO. This apparent puzzle is probably due to real differences in the micro structure of the catalyst support. A series of experimental reductions using a common green catalyst led to very good cor-relations between net activity for fatty acid hydro-genation and the crystallite size and Ni/NiO ratio. On a given support, the crystallite dimension can be modified by the reduction treatment and is not sharply fixed by the selection of nickel salt and sup-port. If the stoichiometric ratio of hydrogen is lowered, the crystallite dimension is reduced, but so is the qualitative efficiency of reduction (Ni/NiO), with the result that an exceptionally small crystallite size catalyst may be less active than one with larger crystals, but with more reduced Ni/unit weight.     

Enantiodifferentiation in asymmetric sonochemical hydrogenations

The effect of sonochemical pretreatment on the enantioselectivity of Pt/Al₂O₃–cinchonidine-catalyzed ethyl pyruvate hydrogenation was studied at different hydrogen pressures in various solvents, mainly in acetic acid. The sonochemical pretreatment of a commercial Pt/Al₂O₃–cinchonidine catalytic system in acetic acid resulted in enhanced enantioselectivity providing excellent ee values (97% ee) under mild and widely varied experimental conditions. Moreover, the application of ultrasonics provides a possibility of the catalyst recycling without regeneration. The catalyst was tested by transmission electron microscopy to determine the effect of the sonication on the metal particle size morphology. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ru催化加氢选择性脱除F-T合成水相中的含氧化合物

采用催化加氢技术脱除F-T合成水相中羧酸、醛、醇、酮、酯含氧化合物,考察了Ru/ZrO₂、Ru/TiO₂、Ru/SiO₂和Ru/Al₂O₃ 4种Ru催化剂的反应性能.相对于酸、醇,水中的醛、酮、酯更易被转化.其中Ru/ZrO₂和Ru/TiO₂具有良好的加氢脱羰活性,在200℃、9.8 MPa、3.0 h^-1空速下,酸、醛、醇、酮、酯均转化为C₁～C₆的烷烃,总转化率达92%.同条件下,虽然Ru/Al₂O₃对酸、醛、酮、酯的转化活性较高(>87%),但对醇的转化不到30%,具有选择性转化特点.H₂-TPR和NH₃-TPD结果表明,Ru/Al₂O₃催化剂的金属活性位与载体酸性位的协同作用有利于羧酸的加氢反应,能抑制醇的加氢脱羰活性;而金属-载体相互作用较弱和酸度较低的催化剂有利于羧酸、醇发生加氢脱羰反应.Ru/Al₂O₃催化剂运行500 h后失活,XRD、SEM和N₂-物理吸附表明,载体结构物相和织构性质的改变以及活性组分的流失是导致催化剂失活的主要因素.     

Electrocatalysis over Pd catalysts: A very efficient alternative to catalytic hydrogenation of cyclohexanone

Electrocatalytic reaction was examined as an alternative method for the catalytic hydrogenation of cyclohexanone over Pd catalysts. The behavior of Pd/alumina catalyst and finely divided Pd catalyst in the electrocatalytic and catalytic hydrogenation of cyclohexanone in aqueous solution were investigated as a comparative study. The role of the pH of the solution was studied both in electrocatalytic and catalytic hydrogenation over Pd/alumina catalyst using acetic acid as a supporting electrolyte. High current yields were obtained for the electrocatalytic process, whereas, as expected from the literature, the catalytic hydrogenation was inefficient.     

Mesoporous Pt–Ni catalyst and their electro catalytic activity towards methanol oxidation

Mesoporous Pt/Ni architecture has been prepared by template assisted electrochemical deposition of Pt–Ni over anodized aluminum oxide template followed by controlled de-alloying with nitric acid. Surface characteristics of the ordered bimetallic mesoporous Pt/Ni structure were systematically characterized through XRD, SEM, AFM and XPS analyses. It is designated by XPS analysis that presence of Ni significantly modifies surface characteristics and electronic states of Pt accompanied with a downshift in the d-band character of Pt. Mesoporous morphology is highly beneficial to offer readily accessible Pt catalytic sites for methanol oxidation reaction. The prepared bimetallic Pt/Ni was used as electro catalyst for DMFC. Comparison of electrocatalytic activity of bimetallic mesoporous Pt/Ni with bimetallic smooth Pt/Ni was interrogated using cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy analyses. Distinctly enhanced electrocatalytic activity with improved CO tolerance associated with bimetallic mesoporous Pt/Ni electrode towards methanol oxidation stems from a synergy existing between mesoporous structure with bi-metallic composition.     

MgAl2O4 spinel prepared by mechanochemical synthesis used as a support of multimetallic catalysts for paraffin dehydrogenation

The catalytic performance in n-butane dehydrogenation of bimetallic PtSn, PtGa and PtIn, and trimetallic PtSnIn and PtSnGa catalysts (with low metal contents) supported on a MgAl₂O₄ prepared by a novel mechanochemical synthesis was evaluated both in flow and pulse equipment. The influence of the addition of different promoters (Sn, Ga and In) to Pt on the activity, selectivity and deactivation in the n-butane dehydrogenation reaction was studied. Stability experiments through successive reaction-regeneration cycles were carried out for selected catalysts. In order to correlate the properties of the metallic phase of the catalysts with the catalytic behavior, several characterization techniques were used, such as test reactions of the metallic phase (cyclohexane dehydrogenation and cyclopentane hydrogenolysis), TPR, XPS, H₂ chemisorption and TEM. Bimetallic PtSn catalyst has a better catalytic behavior than PtIn and PtGa ones. For PtSnM (M: In or Ga) catalysts, whereas Ga addition to the bimetallic catalyst does not practically modify the dehydrogenation performance, the addition of In produces an increase of the activity and the selectivity to butenes. Characterization results indicate the presence of geometric effects for the PtSn catalyst, and geometric and electronic effects for PtIn and PtGa ones. For trimetallic catalysts, the presence of a close contact between Pt, Sn and In or Ga in both trimetallic catalysts was found, mainly due to geometric effects like blocking and dilution of the active sites by the promoters. In stability experiments, the trimetallic PtSnIn/MgAl₂O₄ catalyst clearly displays the best catalytic performance along reaction-regeneration cycles, though PtSnGa and PtSn catalysts also showed a very good behavior through the successive cycles. The characterization of these catalysts after cycles shows that their metallic phases are slightly modified along the cycles.     

Bimetallic PtSn nanoparticles confined in hierarchical ZSM-5 for propane dehydrogenation

A series of PtSn/hierarchical ZSM-5 catalysts were developed for propane dehydrogenation,in which the PtSn bimetallic particles are confined in the mesopores of hierarchical ZSM-5 zeolite.The synthesis of PtSn/hierarchical ZSM-5 catalysts was achieved via the loading of Pt and Sn species onto the hierarchical ZSM-5 catalysts that are obtained through a desilication of conventional ZSM-5.The PtSn/hierarchical ZSM-5 catalysts were fully characterized by XRD,N2 adsorption,STEM,XPS,and CO-IR techniques,which reveals that highly dispersed PtSn bimetallic nanoparticles are enclosed into mesopores of hierarchical ZSM-5.The catalytic performance of PtSn/hierarchical ZSM-5 is greatly affected by the concentrations of alkali solution in the desilication process and Sn/Pt ratios in PtSn bimetallic particles.The PtSn1.00/ZSM-5(0.8) catalyst shows the highest efficiency in propane dehydrogenation,which gives an initial con-version of 46％ and selectivity of 98％ at 570 ℃.The high efficiency in these PtSn/hierarchical ZSM-5 cat-alysts for propane dehydrogenation is mainly ascribed to the confinement of PtSn particles in the mesopores of hierarchical ZSM-5 zeolite.     

One-Step Hydrogenation/Esterification Activity Enhancement Over Bifunctional Mesoporous Organic–Inorganic Hybrid Silicas

Bifunctional mesoporous organic–inorganic hybrid silica incorporating both platinum and organosulfonic acid groups were synthesized for use in simultaneously catalyzing the one-step hydrogenation/esterification (OHE) of acetic acid and acetaldehyde, which was considered as a model reaction for the upgrading of biomass-derived bio-oil. The work explored optimizing the synthesis procedure to generate a bifunctional catalyst with enhanced combined activity for the OHE reaction. The presence of Pt was found to enhance the acidic properties of the organosulfonic acid functionalized silica. The mechanism by which the Pt incorporation affected the acid sites was investigated by the using XPS, FT-IR, FT-Raman characterization. The XPS results indicated the presence of electron transfer between the Pt and –SO₃H groups. The FT-IR and FT-Raman results, which were in agreement with XPS, demonstrated an electron density increase for S and a S–O bond energy increase, which was proposed to be the reason for the acidity enhancement due to the presence of Pt. Additionally, arenesulfonic acid groups were substituted for propylsulfonic acid groups and the resulting material had higher catalytic activity due to the increased acid strength. An optimal synthesis procedure was demonstrated in which the Pt was first impregnated on the mesoporous silica using reductive deposition. Then Pt was activated and the material further modified by grafting on arenesulfonic acid groups. The resulting catalyst was about four times more active than the original base case bifunctional material.