Catalyst Preparation Conditions Research Articles

Effects of Catalyst Precursor Type and Preparation Conditions, and Solvent Type on Activity and Selectivity of Pt/SiO2 Catalyst in Citral Hydrogenation

In this study, citral hydrogenation reaction in liquid phase over silica gel supported Pt catalysts was investigated. It was desired to hydrogenate carbonyl group selectively to produce valuable unsaturated alcohols, namely geraniol and nerol. Pt/SiO2 catalysts were prepared by impregnation method. The effects of parameters investigated in the present study included Pt precursor type (hexachloroplatinic acid (HCLPA), platinum II acetylacetonate (PAA)), catalyst activation temperature (350°C and 450°C), catalyst activation without calcination, catalyst washing with 0.1 M NaOH and solvent type (ethanol, 2-pentanol). The catalysts activities and selectivities were affected by the type of precursor and activation temperature. The maximum citral conversion (89.50 percent) was achieved at lower activation temperature (350°C) with PAA precursor based catalyst. It was observed that higher activation temperature provided lower citral conversion but higher selectivity to unsaturated alcohols; increasing the activation temperature to 450°C decreased citral conversion to 26.10 percent. But selectivity to unsaturated alcohols, geraniol and nerol, increased from 7.06 to 54.60 percent. Catalyst washing and 2-pentanol prevented acetal formation. Catalyst activation without calcination gave lower citral conversion (20.84 percent) and selectivity to unsaturated alcohols (30.00 percent).

Selective hydrogenation of nitrostyrene to aminostyrene over Pt/TiO 2 catalysts: Effects of pressurized carbon dioxide and catalyst preparation conditions

The present work has studied the influence of CO 2 pressurization on the hydrogenation of nitrostyrene (NS) using Pt/TiO 2. With CO 2 pressurization up to 12 MPa (CO 2-dissolved expanded liquid (CXL) phase), the over-all reaction rate and the selectivity to aminostyrene (AS) increased. At higher CO 2 pressures where all NS dissolved in scCO 2 (scCO 2-homogeneous phase), both of them decreased with increasing the CO 2 pressure. The phase behavior was an important factor for the present reaction system. It was also found that the presence of pressurized CO 2 gave higher selectivity to AS than in its absence at any conversion level. This was ascribed to retardation effects of dense phase CO 2 on the hydrogenation of AS to ethylaniline. Competitive adsorption of nitro and vinyl groups was suggested to determine the product selectivity. FTIR measurements showed that the pressurized CO 2 lowers the reactivity of the nitro group, and this effect is stronger in scCO 2-homogeneous phase than in CXL phase, resulting in the lower AS selectivity in the former phase. Lower Pt loadings and higher catalyst reduction temperatures gave Pt/TiO 2 catalysts more selective for the AS formation. FTIR measurements of adsorbed CO over the catalysts suggested that the presence of less-coordinated Pt atoms on edge, corner and kink sites was significant for the selective hydrogenation of NS to AS.

Heterogeneous catalytic degradation of polyacrylamide solution

Degradation of polyacrylamide (PAM) in aqueous solution was studied by using Fe2O3/Al2O3 as heterogeneous catalyst in the presence of H2O2. Effects of catalyst preparation conditions such as impregnated materials and adding different trace metal elements to catalyst activity were studied, respectively. It was observed that compared with FeSO4, the Fe(III) catalyst prepared with Fe(NO3)3 as the impregnated material showed better catalyst activity. Modified with trace metal elements, the catalytic activity of Fe2O3/Al2O3 could be changed greatly. Among various trace metal elements, Fe2O3/Al2O3 catalysts modified with Co and Cu showed great increase on catalytic activity. International Journal of Engineering, Science and Technology, Vol. 2, No. 7, 2010, pp. 110-114

Magnetic characteristics of alumina-supported chromium catalyst modified with Ni, Sb, and K for propane dehydrogenation

The magnetic characteristics and temperature conductivity of the Cr-Ni-Sb-K/γ-Al2O3 catalyst were studied in relation to the catalyst composition and preparation conditions. The correlation between the catalyst activity and its magnetic susceptibility and temperature conductivity was examined.

Selective oxidation of methane into synthesis gas at short contact times on low-loading platinum-ruthenium catalysts

The results of the study of Pt-Ru/2% Ce/(θ + α)-Al2O3 catalysts with various Pt/Ru ratios used in the process of selective methane oxidation into synthesis gas at short contact times are presented. The optimal catalyst preparation conditions have been found for the process. It has been revealed that the methane conversion at 1173 K and a contact time of 4.0-3.0 ms varies from 96 to 100% and the selectivities for hydrogen and CO are 100 and 95–100%, respectively. At a Pt: Ru molar ratio of 2: 1 or 1: 1 and τ = 3.5 ms, the maximum (100%) degree of the conversion of methane into synthesis gas via the direct route is observed; the selectivity for H2 and CO is 100%, and the total content of the noble metals is O ≥ 0.2%.

Self-Made Gas Diffusion Electrodes for Dye Wastewater Treatment

Gas diffusion electrodes (GDEs) were selected for the reactive brilliant red X-3B simulated wastewater treatment, perovskite oxide LaNiO3 as the catalyst. And a satisfying degradation effect was achieved. The optimal conditions for the catalyst preparation with sol-gel method were 1.5 as the molar ratio of citric acid and metal ions, 10 as the pH, and 750 °C as the roasting temperature. The optimal conditions for the electrodes preparation were 1 g pore-forming agent, 0.6 g catalyst, 3 g PTFE and 300 °C as the roasting temperature. Scanning electron microscope, X-ray diffraction were applied to analyze the performance of catalyst and electrodes, and the results were satisfying.

Relationship between the surface characteristics of Pt catalyst and catalytic performance on the H 2 SCR

This research investigated how the physical and chemical properties of Pt/TiO 2-based catalysts with high activity in SCR reaction are affected by the preparation conditions (type of TiO 2, Pt content and calcination temperature) using XRD, BET and TPR analysis. The catalyst preparation conditions that achieve optimum reactivity were identified by examination of how the physical and chemical properties relate to catalytic activity. According to the results, Pt content over 2 wt% causes a phenomenon in which Pt agglomeration increases linearly according to the surface area of the limited support. However, Pt content over 3 wt% showed an increase in reducibility in the low temperature region that is proportional to the absolute amount of Pt has increased. Moreover, although increased calcination temperature did not result in phase transition of the TiO 2 support, it did lead to reduction of the surface area by increasing crystallinity and sintering of Pt.

Production of Synthesis-Gas on Low-Percentage Pt-, Ru- and Pt–Ru Catalysts

The results of research of the Pt-, Ru- and Pt–Ru/2% Ce/(θ + α)-Al2O3 catalysts with various ratio of Pt to Ru for selective catalytic oxidations of CH4 into synthesis-gas at short contact times are presented. Optimum conditions for preparation of catalysts were found. It was established that the CH4 conversion at 1,173 K changes from 96 to 100%, selectivity by H2—100%, and CO—95–100% at contact times 3.0–4.0 ms.

A Review of the Properties and CVD Synthesis of Coiled Carbon Nanotubes

The CVD route for carbon nanotube production has become a popular method to make large amounts of multiwall carbon nanotubes. The structure, morphology and size of carbon materials depend critically on the catalyst preparation and deposition conditions. According to current knowledge, CVD method is the only process which can produce carbon nanocoils. These nanocoils are perfect candidates for nanotechnology applications. One might indeed hope that these coils would have the extraordinary stiffness displayed by straight nanotubes. Based on theoretical studies, regular coiled nanotubes exhibit exceptional mechanical, electrical, and magnetic properties due to the combination of their peculiar helical morphology and the fascinating properties of nanotubes. In spite of its technological interest, relatively low attention has been paid to this special field. In this paper we attempt to summarize results obtained until now.

Effect of Fractal Dimension on CO Selectivity of K−Ni/<i>α</i>-Al<sub>2</sub>O<sub>3</sub> Catalyst for High Pressure Oxidative Reforming of Methane

To suppress total oxidation and increase the CO selectivity of high-pressure oxidative reforming of methane, preparation parameters of K−Ni/α-Al2O3 catalyst were optimized. The target preparation parameters were the main factors affecting CO selectivity such as calcination temperature of γ-Al2O3, and NiO and K loadings. Parameters were designed by L9 orthogonal array containing three factors and three levels, and the catalysts were prepared by the sequential impregnation method with Ni loaded prior to K. Activity test of the L9 catalysts was conducted at 1 MPa and 650°C. The relationship between the preparation conditions and CO selectivity of the L9 catalysts obtained from the experimental results was analyzed using a radial basis function network (RBFN). The CO selectivity was expressed by the RBFN as functions of the catalyst preparation parameters. A grid search, where all combinations of the preparation conditions were input to the RBFN, was conducted to identify the optimum conditions of catalyst preparation for the highest CO selectivity. The predicted catalyst was 1.3 wt% K−14 wt% NiO on α-Al2O3 calcined at 1195°C. Surface NiO morphology was estimated by fractal dimension of Ni distribution in the EPMA image, and X-ray diffraction (XRD) and BET surface area measurements were conducted using the L9 catalysts. These characters were correlated to the catalyst preparation conditions by RBFNs, and the grid data were calculated on the RBFNs. These grid data were analyzed by multivariate analysis to calculate the correlations between CO selectivity, fractal dimension, NiO crystalline parameters, and BET surface area. CO selectivity was expressed by a linear combination of the fractal dimension and NiO crystalline parameters. Another multivariate analysis suggested that fractal dimension was also expressed by primary expression of the NiO diffraction angle, so that the preparation conditions, especially the K loading, affect the NiO diffraction angle. Therefore, K addition was suggested to affect the NiO lattice to modify the surface morphology of NiO resulting in change of CO selectivity.

Influence of ultrasonic on the preparation of Ni–Mo–B amorphous catalyst and its performance in phenol hydrodeoxygenation

The amorphous Ni–Mo–B catalysts were prepared by ultrasonic as well as regular chemical reduction and characterized by BET, SEM, XRD, XPS, and FTIR. Their catalytic activity in the hydrodeoxygenation of phenol was evaluated. The influences of the catalyst preparation conditions and the reaction temperature on the phenol hydrodeoxygenation were investigated, and a reaction mechanism was proposed. The results showed that the particle size, agglomeration phenomenon, surface area, and MoO 2 and B content of the Ni–Mo–B catalysts can be regulated by introducing the ultrasonic treatment into the chemical reduction, which is effective to enhance their catalytic activity in phenol hydrodeoxygenation. At 498 K, the conversion of phenol is 81.08% and the hydrodeoxygenation selectivity reaches 93.39%.

Phosphoric acid modified SBA-15 as a highly efficient heterogeneous catalyst for the synthesis of 4,4′-diamino-3,3′-dibutyl-diphenyl methane

Phosphoric acid modified SBA-15 (P/SBA-15) was employed as catalyst in the synthesis of 4,4′-diamino-3,3′-dibutyl-diphenyl methane (MBTBA) via condensation of o-tert-butylaniline with paraformaldehyde. It performed more efficiently than HY, kaolinite, γ-Al2O3 in heterogeneous reaction and HCl in homogeneous catalysis did. The catalyst preparation and reaction conditions were investigated and the yield reached 50% under the optimized term. The BET and Py-FTIR results suggested that the excellent performance of P/SBA-15 in the synthesis of MBTBA should be attributed to the weak acidity of the material and its large pore size that facilitated the diffusion of substrate and product.

Preparation and Characterization of Catalysts Supported on Catalytically Channeled Carbon Nanofibers for Direct Methanol Fuel Cells

Particularly channeled carbon nanofibers (CNF) were applied to the catalyst support for preparation of electrode catalysts for DMFC. Porous CNFs were prepared through selective gasification of CNF with nano-sized catalyst particles such as Ru under prescribed conditions. The channel width, length, and channeling direction were dependent on the catalyst nature and preparation conditions. The channeled CNFs-supported PtRu catalysts were tested in methanol oxidation and DMFC single cells.

A high-throughput reaction system to measure the gas-phase photocatalytic oxidation activity of TiO2 nanotubes

A sixteen-channel, high-throughput system was designed and built to test the activity of catalysts for gas-phase photocatalytic oxidation of methanol. The system utilizes granular catalyst films to model relevant applications and allow for rapid processing. It is capable of 48 catalyst tests per day using the procedure described herein. Several experiments were performed to minimize both the within-node and between-node variances of the system. Utilizing the high-throughput system, the significance of preparation methods on the photocatalytic activity of TiO2 nanotubes was investigated. A one-half fractional factorial experiment identified the factors that significantly impact catalyst activity as the following: precursor type (Degussa P-25, or nanotubes), platinum loading, the interaction between precursor and dope time, and the interaction between the precursor and calcination temperature. Based on experimental results, catalyst activity is optimized by doping TiO2 nanotubes directly (rather than doping P-25 prior to nanotube formation), a low platinum loading (0.01 wt %), and using a dope time of 30 min followed by calcination at 773 K. The optimum catalyst preparation conditions produced a catalyst that was three times more active than the starting P-25 material.

Pretreatment-Induced Nanostructural Evolution in CeO2-, Sm2O3-, and CeO2/Sm2O3-Supported Pd Catalysts for Intermediate-Temperature Methanol Fuel Cells

Catalysts of 2 wt % Pd supported on CeO2, Sm2O3, and CeO2/Sm2O3 (in a 4:1 molar ratio) were studied in detail by high-resolution transmission electron microscopy and elemental mapping, both as-prepared and after undergoing one of three reduction pretreatments of increasing severity. The evolution in the nanostructure, composition, and disposition of the phases were studied in detail as a function of starting composition and of pretreatment conditions. The trends observed were compared with the trends in activity and selectivity of the catalysts for hydrogen generation from methanol fuel, with a view to their application in direct methanol intermediate-temperature solid oxide fuel cells. The catalyst preparation conditions had a dramatic effect on the Sm-containing materials but not on the Pd/CeO2. The Pd/CeO2/Sm2O3 catalyst was seen to develop a beneficial hierarchical structure in which Pd particles were supported on fine Sm2O3 crystallites, which were in turn supported on larger CeO2 particles. This effect may be useful for the deliberate design of such nanostructured catalysts.

Effects of preparation conditions in hydrothermal synthesis of highly active unsupported NiMo sulfide catalysts for simultaneous hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene

Unsupported NiMo sulfide catalysts were prepared from ammonium tetrathiomolybdate (ATTM) and nickel nitrate by using a hydrothermal synthesis method involving water, organic solvent and hydrogen. The activity of these catalysts in the simultaneous hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) was much higher than that of the commercial NiMo/Al 2O 3 sulfide catalysts. Interestingly, the unsupported NiMo sulfide catalysts showed higher activity for hydrogenation (HYD) pathway than the direct desulfurization (DDS) pathway in the HDS of DBT. The same trends were observed for the HDS of 4,6-DMDBT. Morphology, surface area, pore volume and the HDS activity of unsupported NiMo sulfide catalyst depended on the catalyst preparation conditions. Higher temperature and higher H 2 pressure and addition of an organic solvent were found to increase the HDS activity of unsupported NiMo sulfide catalysts for both DBT and 4,6-DMDBT HDS. Higher preparation temperature increased HYD selectivity but decreased DDS selectivity. High-resolution TEM images revealed that unsupported NiMo sulfide prepared at 375 °C shows lower number of layers in the stacks of catalyst with more curvature and shorter length of slabs compared to that prepared at 300 °C. On the other hand, higher preparation pressure increased DDS selectivity but decreased HYD selectivity for HDS of 4,6-DMDBT. HRTEM images showed higher number of layers in the stack for the NiMo sulfide prepared under an initial H 2 pressure of 3.4 MPa compared to that under 2.1 MPa. The optimal Ni/(Mo + Ni) ratio for the NiMo sulfide catalyst was 0.5, higher than that for the conventional Al 2O 3-supported NiMo sulfide catalysts. This was attributed to the high dispersion of the active species and more active NiMoS generated. The present study also provides new insight for controlling the catalyst selectivity as well as activity by tailoring the hydrothermal preparation conditions.

Adsorption sites of an iron-aluminum catalyst for ammonia oxidation as studied by the IR spectroscopy of the adsorbed NO probe molecule

The state of surface adsorption sites in the IK-42-1 oxide catalyst for ammonia oxidation depending on catalyst preparation conditions (the nature of raw materials and the temperature of calcination) was studied in this work with the use of the diffuse reflectance IR spectroscopy of the adsorbed NO probe molecule. Hematite, which was prepared by a sulfate or chloride technology, was used as the starting raw material; Al2O3 binding agents were prepared by the reprecipitation or hydration of thermally activated gibbsite; and acetic or nitric acid was used as an electrolyte. The samples were calcined at 900–1000°C. It was found that mono- and dinitrosyl complexes with reduced coordinatively unsaturated Fe2+ cations and nitrite-nitrate complexes were formed upon the adsorption of NO on the catalyst surface (regardless of the catalyst preparation conditions). The samples differed in the amount and degree of coordinative unsaturation of adsorption sites depending on the preparation conditions. It was concluded that the most coordinatively unsaturated Fe2+ adsorption sites observed were formed on the surface of a solid solution of iron cations in aluminum oxide, which was formed in the course of catalyst preparation. It was found that an increase in the catalyst calcination temperature resulted in a decrease in the number of coordinatively unsaturated adsorption sites, which correlated with the observed decrease in the yield of NO. This correlation had the shape of a saturation curve, which can reflect the occurrence of a reaction in the diffusion mode at high degrees of conversion for the majority of catalysts.

Conversion of biomass to fuel: Transesterification of vegetable oil to biodiesel using KF loaded nano-γ-Al2O3 as catalyst

KF-impregnated nanoparticles of γ-Al2O3 were calcinated and used as heterogeneous catalysts for the transesterification of vegetable oil with methanol for the synthesis of biodiesel (fatty acid methyl esters, FAME). The ratio of KF to nano-γ-Al2O3, calcination temperature, molar ratio of methanol/oil, transesterification reaction temperature and time, and the concentration of the catalyst were used as the parameters of the study. A methyl ester yield of 97.7±2.14% was obtained under the catalyst preparation and transesterification conditions of KF loading of 15wt%, calcination temperature of 773K, 8h of reaction time at 338K, and using 3wt% catalysts and molar ratio of methanol/oil of 15:1. This relatively high conversion of vegetable oil to biodiesel is considered to be associated with the achieved relatively high basicity of the catalyst surface (1.68mmol/g) and the high surface to volume ratio of the nanoparticles of γ-Al2O3.

Comparison of Genetic Programing, Radial Basis Function Network and Polynomial Equation Used for Response Surface Method for Catalyst Optimization

Preparation conditions of Co-MgO catalyst for methane dry reforming were optimized to maximize the CO yield. Response surface method, composed of design of experiment and regression method, was applied. For the best regression, genetic programing, radial basis function network, and polynomial equation were compared. As a result, genetic programing succeeded to express explicitly the non-linear relationship between catalyst preparation parameters and catalyst performance, and the prediction error was the least. Genetic programing modifies and optimizes many functions by genetic algorithm to fit the experimental results. Radial basis function network could express the non-linear relationship, but the complexity of the function hindered the understanding of the importance of catalytic parameters. While polynomial equation proposed the explicit equation, the accuracy was not sufficient to show the non-linear relationship. Genetic programing is the most suitable regression method of response surface for the catalyst development.

Effect of dispersion and distribution of tungsten on W/HZSM-5 for selective catalytic reduction of NO by acetylene

Catalytic performance of W/HZSM-5 in selective catalytic reduction of NO by acetylene was investigated in a reaction system with 1600 ppm of NO, 800 ppm of C 2H 2, and 9.95% of O 2 in He. It was found that promotional effect of tungsten on the reaction is strongly affected by catalyst preparation conditions and Si/Al ratio of the parent zeolite. A better dispersion of tungsten on HZSM-5 and relatively more monomeric tungsten species were found on 8%W/HZSM-5 prepared by impregnation of the zeolite with lower SiO 2/Al 2O 3 ratio (25) in ammonic ammonium tungstate solution and calcination of the resulting material at higher temperature (550°C). The highest NO conversion to N 2 of 86.3% in the reaction system was obtained at 350°C over the catalyst thus prepared. The mechanism of monomeric tungsten species improving the C 2H 2-SCR can be attributed to accelerating the formation of active nitrate species.