Course Of Catalyst Preparation Research Articles

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.

Activity, stability and characterization of NO oxidation catalyst Co/KxTi2O5

Co/KxTi2O5 catalyst with well-dispersed nano-Co3O4 particles, synthesized by an ion exchange method from K2Ti2O5 precursor, showed extremely high NO oxidation activity and good stability. Morphological changes and microcosmic processes during the course of catalyst preparation were examined using atomic absorption spectrometry (AAS), X-ray diffraction (XRD), and scanning electron microscopy-energy dispersive X-ray (SEM-EDX). During the ion exchange of K2Ti2O5 with Co precursor solution, K+ ions were replaced by H+ (H3O+). After calcination at 500°C, a partially collapsed structure was obtained when the exchange was controlled to a certain degree. Fortunately, the Co that precipitated on this collapsed structure formed highly stable nano-particles of Co3O4. Catalytic activity for the NO oxidation was found to be highly dependent on the loading and particle size of Co and K remaining in the KxTi2O5 support.

Selective reduction of NO x by hydrogen and methane in natural gas stationary sources over alumina-supported Pd, Co and Co/Pd catalysts : Part A. On the effect of palladium precursors and catalyst pre-treatment

The aim of the present work is to study the selective reduction of NO x from natural gas sources. The unburned methane can be used as reductant. Another reductant such as hydrogen can be created in situ, using a microreformer. The results suggest that the NO x are reduced by H 2 at low temperature, when methane is not activated and at higher temperature the methane is then the main reductant. However, the catalytic behaviour depends on the metal precursor and the catalyst treatment. The most prominent result is obtained on the palladium catalyst prepared from Pd(NH 3) 4(NO 3) 2 precursor. Comparing the reduction and the calcination step in the course of catalyst preparation, one can conclude that calcination lead to the higher activity in deNO x , since reduced catalysts are oxidized during the deNO x process.

Effect of Polyethylene Glycol Addition on Hydrodesulfurization Activity over CoO-MoO<sub>3</sub>/Al<sub>2</sub>O<sub>3</sub> Catalyst

A new additive approach using polyethylene glycol (PEG) as a water soluble organic compound was proposed to improve hydrodesulfurization activity over CoO-MoO3/Al2O3 catalyst. The addition of PEG to the impregnation solution during the course of catalyst preparation significantly improved thiophene, dibenzothiophene and light gas oil hydrodesulfurization activity. XPS and TEM measurements indicated that the positive effect of PEG can be attributed to suppression of cobalt and molybdenum aggregation and increasing the number of active sites. Without PEG addition, the cobalt and molybdenum precursors tended to aggregate during the drying step due to weak interaction with the alumina support. Addition of PEG to the impregnation solution maintained high dispersion of cobalt and molybdenum precursors on the alumina support even after water removal, since PEG has higher boiling point than water. Consequently, higher dispersion of cobalt and molybdenum was maintained, because they remained dissolved in the PEG.

Structure of a Platinum–Alumina Catalyst Prepared from the Carbonyl Cluster H2[Pt3(CO)6

The state of a platinum carbonyl cluster in an initial aqueous acetone solution and its transformations on the surface of aluminum oxide in the course of catalyst preparation were studied by EXAFS spectroscopy. It was found that water enters the polynuclear framework of the dissolved cluster (the Pt–O distance is 2.55 A, where O is the oxygen atom of water). Structural changes in the supported cluster in the course of catalyst preparation exhibited a strong interaction of platinum with alumina (the Pt–O distance is 1.92–1.95 A), beginning at the step of H2[Pt3(CO)6]5 adsorption. This interaction was retained upon the subsequent high-temperature treatments of the catalyst. The structures of samples prepared from platinum carbonyl and chloroplatinic acid were significantly different. In the former case, a surface prototype was formed from the initial cluster; in the latter case, the sample consisted of platinum metal clusters of a considerable size.

Optimum washing conditions for the preparation of Cu/ZnO/ZrO2 for methanol synthesis from CO hydrogenation: Effects of residual sodium

The residual sodium in the Cu/ZnO/ZrO2 catalyst is found to inhibit the interaction between CuO and ZnO and lead to a decrease in the catalytic activity for CO hydrogenation. Therefore, it is required to reduce the content of sodium as much as possible during the course of catalyst preparation. To obtain 10% yield of methanol, the sodium content must be reduced to a level lower than 0.15%. For this purpose, the washing condition has been investigated experimentally to optimize the preparation conditions of Cu/ZnO/ZrO2 catalyst. As a result, the sodium content could be reduced to 0.115% by washing the cake four times with 50 mL of distilled water per gram of the cake, which constitutes the optimum condition for washing.

Characterization of K 2CO 3/Co–MoS 2 catalyst by XRD, XPS, SEM, and EDS

MoS 2, Co–MoS 2 and K 2CO 3/Co–MoS 2 catalysts have been characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). XRD analysis indicates that Co–MoS 2 is a primary phase in K 2CO 3/Co–MoS 2 catalyst and the diffraction lines of Co–MoS 2 are not changed by the addition of K 2CO 3. Co 9S 8 phase is not present at Co/Mo mole ratio of 0.5 using a co-precipitation method for preparation of cobalt–molybdenum catalyst. The binding energies (BEs) of chemical species present on the surface of the catalysts are compared through the course of catalyst preparation. K 2CO 3/Co–MoS 2 catalyst has been investigated as a function of dispersion of K on the surface and exposure to a mixture of carbon monoxide and hydrogen (syngas) by scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). The distribution of potassium on the surface of the K-promoted catalyst is not uniform.

Ziegler‐Natta polymerization of ethylene with Ti‐Mg catalysts anchored on polymeric supports

AbstractThe immobilization of Ti‐Mg catalysts via polymeric Grignards on crosslinked polystyrenes has been achieved in the presence of methylene spacers of varying length. The resulting catalysts are tested in the homopolymerization of ethylene in a suspension process at 85°C and a total pressure of 6 bar. Hydrogen has been used as molecular weight controlling agent. The polymerization activity of the catalysts is significantly enhanced when a MgCl2 phase is generated in the course of catalyst preparation. The results are supported by SEM and TEM techniques.

Enhancement of methanation activity by ammonia-water vapor treatment at the stage of catalyst-metal salt supported on a carrier

In the course of catalyst preparation by impregnation of a porous support with catalyst-metal salts, an NH 3-H 2O vapor (AW) treatment was performed before the decomposition of the salts. Salts of various Group VIII metals, and mixed salts of an iron-group metal and lanthanum, were used. For Ni(N0 3) 2, Ni(N0 3) 2-La(N0 3) 3, Ni(CH 3COO) 2 and Co(N0 3) 2-La(N0 3) 3, the resulting catalyst exhibited higher methanation activities as a result of the AW treatment. In these cases, an ammonium complex was formed with gelatinous eduction and the decomposition temperature decreased by about 20°C, resulting in a higher dispersion of catalyst particles. On the other hand, in the cases of NiCl 2, H 2PtC1 6 and PdCl 2, the methanation activities of the resulting catalysts were decreased by the AW treatment. In these cases, the ammonium complex formed larger and better defined crystals which produced larger catalyst particles of low catalytic activity.

Study of molybdenum valence states in molybdenum oxide catalysts by electron spectroscopy (ESCA)

The valence states of molybdenum in molybdenum oxide catalysts supported on γ-Al2O3 have been studied by the ESCA technique. Molybdenum oxide was found to interact with aluminium oxide in the course of catalyst preparation at 1000°C. In a freshly prepared catalyst molybdenum is present primarily in the hexavalent state. In the reduced catalyst Mo6+, Mo5+ and Mo4+ are present.