Preparation of Cu/ZnO catalyst using a polyol method for alcohol-assisted low temperature methanol synthesis from syngas

A polyol method was used to prepare Cu/ZnO catalysts for alcohol-assisted low temperature methanol synthesis from syngas. Unlike conventional low temperature methanol synthesis, ethanol was employed both as a solvent and a reaction intermediate. Catalyst characterization revealed that Cu/ZnO catalysts were successfully and efficiently prepared using the polyol method. Various preparation conditions such as PVP concentration and identity of ZnO precursor strongly influenced the catalytic activity of Cu/ZnO catalysts. Copper dispersion and catalyst morphology played key roles in determining the catalytic performance of the Cu/ZnO catalyst in alcohol-assisted low temperature methanol synthesis. A high copper dispersion and platelike Cu/ZnO structure led to high catalytic activity. Among the catalysts tested, 5_Cu/ZnO_Zn(Ac)₂ had the best catalytic performance due to its high copper dispersion.     

Preparation of Highly Dispersive Platinum Catalysts Impregnated on Titania-Incorporated Silica Support

Highly dispersive silica-impregnated platinum catalysts were prepared by incorporating titania to the surface of silica support and by treating the impregnated platinum precursor with hydrogen peroxide. High dispersion of platinum on the titania-incorporated silica support was confirmed by XRD, TEM, EXAFS, and X-ray photoelectron spectroscopy (XPS) techniques. The platinum particles dispersed on silica ranged from 1 to 2 nm in size, although the loading amount of platinum was as high as 4 wt.%. The strong interaction between platinum and titania suppressed the migration and aggregation of the platinum particles on the surface, retaining a high dispersion of platinum. The platinum catalysts impregnated on the titania-incorporated silica showed higher catalytic activities in the combustion of methane than the platinum catalysts impregnated on the silica, while their catalytic activities were poor in the hydrogenation of nitrobenzene. Platinum dispersions and catalytic activities of the platinum catalysts on the silica support were discussed in relation to the strong interaction between platinum and titania.     

Synthetic kenyaite as catalyst support for hydrocarbon combustion

Synthetic kenyaite is prepared in the system K₂O–SiO₂–H₂O. It is modified with cobalt and platinum in order to obtain catalysts for complete oxidation of n-hexane and benzene. The prepared samples are characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry (TG), differential thermal analysis (DTA), temperature programmed reduction (TPR) and Fourier transformed infrared (FTIR) spectroscopy. Co is loaded on kenyaite using ammonia method and classical impregnation. Bimetallic Co–Pt possess higher catalytic activity than monometallic cobalt for the oxidation of benzene, while, for hexane oxidation, the monometallic cobalt catalysts exhibit higher or close activity to that of Co–Pt samples. The catalysts prepared by ammonia method have better performance due to finer dispersion of the metal particles on the surface of the support.     

过渡金属对Pt/SiC催化剂上CO氧化性能的影响

以SiC为载体、Pt为活性组分、过渡金属Fe、Co和Ni为助剂,采用浸渍法制备CO氧化催化剂。考察浸渍方法、助剂及其负载量、空速和催化剂焙烧温度等对Pt/SiC催化剂性能的影响。结果表明,助剂的加入提高了活性组分Pt在载体表面的分散度,并产生一定的相互作用,从而提高了催化剂活性,其中,铁助剂的助催化效果较好。共浸渍法制备的催化剂的催化活性优于分步浸渍法,Pt-Fe/SiC催化剂制备中焙烧温度500 ℃时,催化剂活性较佳,适量Fe助剂的添加能够显著提高Pt/SiC催化剂的活性。     

Adsorption and reduction of nitrate in water on hydrotalcite-supported Pd-Cu catalyst

The hydrotalcite-supported Pd-Cu catalysts were successfully prepared by the impregnation or coprecipitation method, and their adsorption and catalytic reduction activity for nitrate in water were evaluated. The catalysts were characterized by X-ray diffraction (XRD) and surface area (BET) analysis. The results demonstrated that hydrotalcite-supported Pd-Cu catalysts could significantly adsorb nitrate ions, and then, effectively catalytically reduce them. The excellent adsorption ability for nitrate resulted from the regenerated layer structure of calcined hydrotalcite catalyst in nitrate aqueous solution. Nitrate was forced into the interlayer space and adsorbed on the external surface. The adsorption kinetics and the adsorption isotherm could be well described by pseudo-second-order model and the Langmuir model, respectively. The comparison of catalytic reduction with the adsorption for nitrate indicated that catalytic hydrogenation activity for nitrate increased with increasing adsorption capacity; nitrate reduction on hydrotalcite-supported Pd-Cu catalysts was a consecutive and dynamic adsorption and catalytic hydrogenation process. In addition, the catalyst obtained by coprecipitation method, with intact regeneration of hydrotalcite structure and a high dispersion of active metals, hold higher adsorption and catalytic activity than that prepared by co-impregnation method.     

Effects of preparation variables on the activity of alumina-supported platinum catalysts for liquid phase cinnamaldehyde hydrogenation

Alumina-supported platinum catalysts were prepared through different metal loading and reduction procedures. The platinum precursors were loaded by impregnation and ion-exchange and then reduced by hydrogen at high temperatures and by sodium tetrahydroborate solution at a low temperature of 35°C. The low-temperature reduced (LR) catalysts were found to produce cinnamyl alcohol in high selectivities in the liquid phase hydrogenation of cinnamaldehyde, irrespective of the method of metal loading. The high-temperature reduced (HR) catalysts prepared with ion-exchange produced hydrocinnamaldehyde and cinnamyl alcohol; the selectivity of the former was larger than that of the latter. In contrast, the HR catalysts prepared with impregnation produced large amounts of by-products and small amounts of hydrocinnamaldehyde and cinnamyl alcohol. When these HR catalysts were additionally treated with sodium tetrahydroborate solution, they indicated product distributions similar to the LR catalysts.     

不同前体制备Ni催化剂及其在硫碘制氢中催化分解HI的性能

硫碘制氢是目前最有潜力的大规模低成本制氢方法之一。HI催化分解是硫碘制氢的关键步骤。本文采用4种具有代表性的镍盐前体--硝酸镍[Ni（NO₃）₂]、乙酸镍[Ni（CH₃COO）₂]和两种有机金属络合镍（乙酰丙酮镍[Ni（acac）₂]和亚硝酸三乙二胺合镍（[Ni（en₃）]（NO₂）₂）制备Ni催化剂,考察了不同镍盐前体对制备的Ni催化剂特性的影响规律以及Ni催化剂在HI催化分解中的性能。采用了BET、XRD和TEM等分析测试技术对制备的Ni催化剂进行了表征。研究结果表明,镍盐前体对制备的Ni催化剂的分散度、催化活性以及催化稳定性有重要的影响。以Ni（NO₃）₂和[Ni（en₃）]（NO₂）₂为前体制备的Ni催化剂具有良好的Ni金属分散度,Ni颗粒分散均匀且尺寸较小。由于高温和强腐蚀的反应环境（HI-I₂-H₂O体系）,Ni催化剂经过反应都会出现不同程度的失活。以[Ni（en₃）]（NO₂）₂为前体制备的Ni催化剂表现出最好的催化活性和稳定性,有望成为未来大规模硫碘制氢系统中HI分解的催化剂。     

Carbon cryogel as support of platinum nano-sized electrocatalyst for the hydrogen oxidation reaction

The kinetics of hydrogen oxidation reaction was studied in perchloric acid solution on carbon-supported Pt nanoparticles using the rotating disk electrode technique. Carbon cryogel and commercial carbon black. Vulcan XC-72 were used as catalyst supports. Pt/C catalysts were prepared by a modified polyol synthesis method in an ethylene glycol (EG) solution. Considerable effect has been observed for the specific surface area of carbon support on the fundamental properties of Pt/C catalyst, such as catalyst particle size distribution and dispersion as well as catalytic activity for the oxidation of hydrogen. X-ray diffraction (XRD) and transmission electron microscopy (TEM) images show that the particle size of the catalyst decreases with the increase of specific surface area of carbon support. Cyclic voltammetry (CV) was used for determination of the actual exposed surface area of catalyst particles. It was found that Pt catalyst prepared by using the novel carbon material displayed better hydrogen electrochemical oxidation activity than the catalyst prepared by using Vulcan XC-72.     

Structural Features and Catalytic Properties of Pt/CeO2Catalysts Prepared by Modified Reduction-Deposition Techniques

The structural features and catalytic properties of Pt/CeO₂catalysts prepared by liquid phase reduction-deposition techniques with formaldehyde and ethylene glycol as reducing agents, respectively, were investigated. TPR and CO pulse titration measurements revealed that smaller particle size and uniform dispersion of platinum were achieved by modified polyol preparation process, which is beneficial to generate appropriate Pt-O-Ce chemical bonding. XPS analysis further demonstrated the presence of strong metal-support interaction in above Pt/CeO₂catalyst. It was observed that the reducing ability and the solvent effect play important roles in controlling the formation of nuclei as well as its growth rate. The sample prepared by modified polyol method exhibited higher catalytic activities and longer stability for the complete oxidation of dimethyl ether than Pt/CeO₂catalyst prepared by HCHO liquid phase reduction.     

The effect of preparation variables on the dispersion of supported platinum catalysts

The effects of several preparation variables on the dispersion of supported platinum catalysts were examined in this study. Supported catalysts were prepared using two different platinum salts, four high surface area support materials, and two aqueous deposition techniques. The catalysts were characterised by hydrogen chemisorption, oxygen chemisorption, and the hydrogen titration reaction. In addition, X-ray diffraction measurements were conducted on all catalysts. Results from this study show that one of the platinum salts, chloroplatinic acid, always gave an equally or more highly dispersed catalyst than the other salt, tetraammine platinum (II) nitrate. The incipient wetness preparation technique produced equal or better dispersions than did the excess water method, with the possible exception of the silica-alumina support. The highest dispersions were attained with alumina, and the lowest with carbon. In some samples, a lack of good agreement existed between X-ray diffraction and chemisorption measurements of crystallite size which indicated broad or bimodal particle size distributions. However, these X-ray data were qualitatively helpful in understanding the unusual chemisorption behaviour of Pt/C catalysts, one of which had a dispersion higher than any previous reported Pt/C catalyst prepared by aqueous impregnation techniques. Experiments were also conducted which showed that either a 1 h or a 12 h treatment in hydrogen at 723 K was sufficient to reduce the platinum salt, and 1 h or 12 h evacuations at 698 K gave similar results. Finally, it was found that approximately one-half of the hydrogen monolayer on supported Pt could be removed by evacuating for 1 h at 300 K.     

临界点干燥仪制备的Pt-P25的电催化析氢反应性能探究

在各种制氢工艺中,电解水是一种获得氢能源的重要途径,Pt是析氢反应(HER)中最理想的催化剂.由于Pt基材料的稀缺性和高成本限制了其大规模应用,因此迫切需要开发一种低含量、高效的铂催化剂.P25是一种晶格缺陷密度很高的混晶型TiO2,载流子浓度大,具有良好的催化效果.本文采用临界点干燥仪,以商业化混晶TiO2(P25)...     

Dispersion Improvement of Platinum Catalysts Supported on Silica, Silica-Alumina and Alumina by Titania Incorporation and pH Adjustment

Platinum catalysts supported on silica, silica-alumina and alumina supports were prepared using four different cationic and anionic platinum precursors in order to examine the contribution of the precursors and supports to the platinum dispersion. The pH adjustment of the precursor suspension to obtain an opposing surface charge of the support to that on the platinum precursor ions considerably improved the platinum dispersion by strengthening their adsorption on the support. However, exceptional platinum dispersion was achieved, regardless of the precursor and support, by simultaneous pH adjustment and titania incorporation on the supports. The increase in the interaction between the platinum precursor and the titania-incorporated support raised the dispersion and stability of the platinum catalysts with high-loading, even after reduction at 400 °C. The physico-chemical states of platinum and titanium were investigated by XRD, TEM, XAFS spectroscopy and CO adsorption technique. The platinum catalysts supported on the titania-incorporated supports with pH adjustment exhibited highly dispersed platinum particles ranging in size from 1 to 3 nm. They also exhibited high catalytic activity in the oxidation of carbon monoxide because of its incorporated titania and partially oxidized, small platinum particles.     

Hydrogenation of vegetable oil using highly dispersed Pt/γ-Al2O3 catalyst: Effects of key operating parameters and deactivation study

In the present work, Pt/γ-Al₂O₃ catalysts with high metal dispersion were prepared and characterized using chloroplatinic acid and platinum acetylacetonate as metal precursors. The activity and selectivity of the catalysts were evaluated in the hydrogenation of sunflower oil. A comprehensive analysis of the effects of key operational parameters on catalytic performance was carried out. The experimental variables were hydrogen pressure (275.8–551.6 kPa), temperature (160–200°C), and catalyst loading (0.005–0.015 kg Pt_exp/m³_oil). Platinum catalysts were active, with a double bond conversion of 28% at 2 h. The metal precursor affected catalyst selectivity. The catalyst prepared with chloroplatinic acid exhibited a lower formation of trans-isomers compared with Pt acetylacetonate. The γ-Al₂O₃ supported platinum catalyst with a metal loading of 0.51 wt.% and a metal dispersion of 98% maintained its initial catalyst activity and selectivity after 10 consecutive uses (1200 min accumulate operation time), without changes in its catalytic properties. The obtained results suggested that Pt catalysts are an attractive alternative to conventional nickel catalysts for the hydrogenation of vegetable oil.     

Cu-silicalite-1 catalyst for the wet hydrogen peroxide oxidation of phenol

The aim of the present work is to study the heterogeneous wet hydrogen peroxide catalytic oxidation (WHPCO) of phenol using copper bearing Silicalite-1 type zeolite, prepared by direct hydrothermal synthesis. The catalysts used for this study were three: one (Na)Cu-Silicalite-1 and two (H)Cu-Silicalite-1 prepared by different ion exchange methods. The results on catalytic activity for phenol abatement and hydrogen peroxide consumption of these materials are presented. The copper leaching during the reaction was evaluated for all samples. A comparison with the catalytic activity and stability of a Cu-Silicalite-1 material prepared by ionic exchange method is presented.     

EXPERIMENTAL STUDY OF CHARACTERISTICS OF Pt/TiO2 CATALYST

Chemisorption of hydrogen, carbon monoxide, and oxygen on 2 wt% Pt/TiO₂ was investigated to determine a satisfactory method for measuring the platinum dispersion on titania. The reduction of Pt/TiO₂ at high temperature results in sharp decrease in hydrogen and carbon monoxide chemisorption capacities and catalytic activity which cannot be accounted for by metal sintering. Oxidation-reduction treatments restore the usual properties of the catalyst. The TPD spectrum of hydrogen on Pt/TiO₃ shifts to higher temperature upon reduction at high temperature and shifts again to its original position upon oxidation. Shift of TPD spectrum does not appear in other catalysts. Oxygen adsorption method is inaccurate to measure crystallite diameter of platinum because oxygen uptake is enhanced not only due to reduced nonstoichiometric oxide support but also to penetration of oxygen into bulk platinum. Hydrogen chemisorption method, however, is a satisfactory technique to measure the platinum dispersion only if the strong metal-support bonding has been destroyed completely. Sintering rate in oxygen is greater than that in hydrogen regardless of the nature of the supports, and sintering resistance of Pt/TiO₂ in hydrogen is much greater than that of other supported platinum catalysts whereas stability of the platinum in oxygen is not dependent on the supports. The influence of chlorine in the presence of oxygen on the redispersion phenomena is found to be very important.     

新型CuO/ZnO催化剂的制备及其在水煤气变换反应中的应用

首次采用沉积沉淀法,以Cu（OH）₂为前驱体制备不同CuO负载质量分数的CuO/ZnO水煤气变换（WGS）催化剂,并运用XRD、N₂物理吸附和TPR等方法对催化剂进行结构表征。结果表明,活性组分CuO在载体ZnO表面的分散程度、颗粒大小及CuO和ZnO之间相互作用对催化剂的活性均有影响。CuO的适宜负载质量分数为20％,所得CuO/ZnO催化剂样品WGS反应活性较好,在350 ℃,CO转化率可达95.5％。     

Characterization of the Active Sites on Pt-Loaded ZSM-5 (Pt/ZSM-5) Prepared by an Ion-Exchange Method for the Oxidation of CO at Low Temperatures

Highly dispersed Pt-loaded ZSM-5 (Pt/ZSM-5) catalysts were prepared by a combination of ion-exchange and thermal pretreatment in different temperatures under vacuum. Highly dispersed ion-exchanged Pt²⁺ ions were reduced into Pt⁺ and then Pt⁰, sustaining their high dispersion state with an increase in the thermal pretreatment temperatures up to 773 K. Thus, prepared Pt⁰ highly dispersed in the cavities of ZSM-5 exhibited high catalytic activity for the oxidation of CO with N₂O at 273?K. However, pretreatment at temperatures higher than 973 K led to the aggregation of highly dispersed Pt⁰ clusters, resulting in a decrease in the catalytic activity for low-temperature oxidation.     

新型Ru基催化剂的制备及其2-乙基蒽醌加氢性能

通过等体积浸渍法和多元醇法制备了负载型钌氧化铝催化剂（Ru/Al₂O₃-IMP和Ru/Al₂O₃-CRP）,并首次探究了其在2-乙基蒽醌（2-eAQ）加氢催化反应中的性能。实验发现,在不同的反应条件（温度、压力、时间）下,Ru/Al₂O₃-CRP催化剂催化2-eAQ加氢反应的活性均高于Ru/Al₂O₃-IMP催化剂。采用电感耦合等离子体原子发射光谱（ICP-AES）、X射线衍射（XRD）、透射电镜（TEM）、光电子能谱（XPS）等分析技术对两种催化剂进行了结构表征。XRD和TEM表征结果发现,Ru/Al₂O₃-CRP催化剂表面的Ru金属颗粒具有高分散性且颗粒尺寸分布较窄。此外,XPS表征结果证实Ru/Al₂O₃-CRP催化剂上钌的电子云密度低,这使得它对2-eAQ上氧孤对电子有着强的吸引力,有利于活化2-eAQ,进而表现出强的加氢反应活性。     

Selective propane dehydrogenation to propylene on novel bimetallic catalysts

Platinum catalysts (0.1–0.2% of Pt) supported on corundum and promoted by indium and tin were prepared, characterized by XPS, XRD, TEM and chemisorption and tested in propane dehydrogenation at 500–580°C with steam and hydrogen as diluents. The characteristics of samples based on corundum were compared with catalysts of similar composition supported on θ-alumina. The catalytic performance in steam was superior by far to that in hydrogen. Coking of corundum-supported catalysts decreased by a factor of 30–60 so their stability was much higher than with θ-supported catalyst. For the first time high dispersion and high activity of corundum-based dehydrogenation catalysts are reported.     

Performance and characterization of supported metal catalysts for complete oxidation of formaldehyde at low temperatures

Activities of a series of metals (Pt, Pd, Rh, Cu, Mn) supported on TiO₂ were investigated for the catalytic oxidation of formaldehyde. Among them, Pt/TiO₂ was found to be the most promising catalyst. Nitrogen adsorption, hydrogen chemisorption, X-ray diffraction (XRD), transmission electron microscopy (TEM) and temperature programmed reduction (TPR) by H₂ were used to characterize the platinum catalysts. Using Ce_0.8Zr_0.2O₂, Ce_0.2Zr_0.8O₂, SiO₂ as supports instead of TiO₂, the activity sequence of 0.6 wt.% platinum with respect to the supports is TiO₂ > SiO₂ > Ce_0.8Zr_0.2O₂ > Ce_0.2Zr_0.8O₂, and this appears to be correlated with the dispersion of platinum on supports rather than the specific surface areas of the catalysts. Platinum loading on TiO₂ has a great effect on the catalytic activity, and 0.6 wt.% Pt/TiO₂ catalyst was observed to be the most active, which could be attributed to the well-dispersed platinum surface phase. The reduction temperature greatly affects the particle size and, consequently, the catalytic activity. The smaller particle size of platinum, due to its high dispersion on support, has a positive effect on catalytic performance. Increasing formaldehyde concentration and space velocity exhibits an inhibiting effect on the catalytic activity.