Redox behavior of V/MgO catalyst in H2S wet oxidation at room temperature

The room temperature wet catalytic oxidation was conducted in a batch reactor with V/MgO catalyst. The XRD study of the catalyst used indicated that V/MgO could not only oxidize H2S to sulfur selectively, but also prevent the sulfidation of metal oxide effectively at the room temperature. The XPS study indicated that the H2S oxidation with V/MgO could proceed by a redox mechanism (V⁵⁺↔ V⁴⁺) and that V³⁺ formation (V⁴⁺→ V³⁺), was responsible for the deactivation of V/MgO. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of potassium addition on bimetallic PtSn/θ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst for dehydrogenation of propane to propylene

PtSn/θ-Al₂O₃ catalysts with different amounts of K (0.14, 0.22, 0.49, 0.72, and 0.96 wt%) are prepared to investigate the K effects on the PtSn catalyst in propane dehydrogenation (PDH). KPtSn catalyst with 0.xx wt% K, 0.5 wt% Pt and 0.75 wt% Sn is designated as xx-KPtSn. PDH was performed at 873 K and a gas hourly space velocity (GHSV) of 53,000 mL/g_cat h. The temperature-programmed desorption (NH₃-TPD), temperature-programmed reduction (TPR) and CO chemisorption of the KPtSn catalysts with K added revealed the potassium addition blocked the acid sites, promoted the reduction of Sn oxide and decreased the Pt dispersion. The formations of cracking products and higher hydrocarbons on acid sites were suppressed by the K effect of blocking the acid sites. In contrast, K addition at more than 0.72 wt% rather increased cracking products and the amount of coke, resulting in the severe deactivation of catalysts. The high cracking products on the KPtSn catalysts with the high amount of K should not be related to the acid sites, because the acid sites were monotonously decreased with an increase in the amount of K. Instead, the potassium affected the characteristics of PtSn. The interaction between Pt and Sn could be weakened by enriching the reduced Sn, because the K component promoted the reduction of Sn oxide in the TPR experiments. Therefore, the 14-KPtSn catalyst with the low amount of K exhibits the highest stability and selectivity among the prepared KPtSn catalysts due to the compromise of the advantageous (blocking the acid sites) and bad (weakening the interaction between Pt and Sn) effects of the K addition in PDH.     

Catalytic Systems for the H<Subscript>2</Subscript>S Wet Oxidation at room Temperature

The catalytic wet oxidation process is the most attractive process for small-scale hydrogen sulfide (H₂S) removal from natural gas. The catalytic wet oxidation process is anticipated to be cost effective and simple so that it can be used for treating sour gases containing small amounts of H₂S and can be easily operated even in isolated sites. The development of effective catalyst is the key technology in the wet catalytic oxidation of H₂S. The scale of operation for the process has to be flexible so its use will not be limited by the flow rates of the gas to be treated. The heterogeneous catalytic wet oxidation of H₂S has been attempted on activated carbons, but the H₂S removal capacity still shows the low removal efficiency. The catalytic wet oxidation of H₂S was studied over Fe/MgO for an effective removal of H₂S. In order to develop a sulfur removal technology, one has to know what surface species of catalyst are the most active. This article discusses the following systematic studies: (i) the catalytic preparation to disperse Fe metal well on MgO support for enhancing H₂S removal capacity, (ii) the effect of the catalytic morphology on the activity of Fe/MgO for the H₂S wet oxidation, (iii) the influence of precursor and support on the activity of Fe/MgO for catalytic wet oxidation of H₂S to sulfur.     

Magnesium oxide as an effective catalyst in catalytic wet oxidation of H2S to sulfur

Four different magnesium oxides were studied in the wet oxidation of H₂S to sulfur. The H₂S removal capacity of MgO in the catalytic wet oxidation strongly depends on the pore size distribution. The MgO with relatively large pores (>100 ?) showed a high removal capacity of H₂S. It is suggested that the large pore size favors H₂S removal in the catalytic wet oxidation due to the limitation of diffusion. This revised version was published online in August 2006 with corrections to the Cover Date.     

Formation of CdO films from chemically deposited Cd(OH)2 films as a precursor

Formation of cadmium hydroxide at room temperature onto glass substrates from an aqueous alkaline cadmium nitrate solution using a simple soft chemical method and its conversion to cadmium oxide (CdO) by thermal annealing treatment has been studied in this paper. The as-deposited film was given thermal annealing treatment in oxygen atmosphere at 450 °C for 2 h for conversion into cadmium oxide. The structural, surface morphological and optical studies were performed for as-deposited and the annealed films. The structural analyses revealed that as-deposited films consists of mixture of Cd(OH)₂ and CdO, while annealed films exhibited crystalline CdO. From surface morphological studies, conversion of clusters to grains after annealing was observed. The band gap energy was changed from 3.21 to 2.58 eV after annealing treatment. The determination of elementals on surface composition of the core-shell nanoparticles of annealed films was carried out using X-ray photoelectron spectroscopy (XPS).     

Methanol dehydration to produce dimethyl ether over g-Al2O3

Summary The kinetic data of about 150 points for methanol dehydration were obtained at the temperature of 240~270^oC, the GHSV of 25,000~120,000 (mL/g_cat./h) and under atmospheric pressure. The data were fitted into six plausible equations. The kinetic equation derived from the molecular adsorption of methanol on two sites fit the kinetic data best, however, that from the dissociative adsorption of methanol could not be safely ruled out. The activation energy of 114.7 kJ/mol for methanol dehydration on γ-Al₂O₃ was obtained from the kinetic analysis.     

Mössbauer and Neutron Diffraction Studies on Co–Al Ferrite

Hyperfine Interactions - Al substituted CoAl x Fe1?x O4 (x=0.1, 0.2, 0.3, and 0.5) have been studied with X-ray and neutron diffraction, Mössbauer spectroscopy and magnetization...     

Influence of copper precursors in the steam reforming of methanol over Cu/SnO2/SiO2 catalysts

Cu/SnO₂/SiO₂ catalysts, prepared with three different copper precursors (copper nitrate, sulfate and chloride), were characterized and investigated for the steam reforming of methanol. Cu/SnO₂/SiO₂ catalyst, prepared with copper nitrate, showed the highest activity among the tested catalysts. The highest activity of the catalyst prepared with copper nitrate was ascribed to the highly dispersed Cu particles from CO adsorption experiment. The selectivity of methanol to H₂ decreased with an increase in the amount of acid on the surface of Cu/SnO₂/SiO₂ catalysts from FT-IR experiments.This revised version was published online in December 2005 with corrections to the Cover Date.     

Catalytic ozonation of humic acids with Fe/MgO

Summary Degradation of humic acids by ozone was performed at room temperature in a stirred tank reactor with heterogeneous catalysts. Experimental results show that the ozonation with Fe/MgO induced a significant reduction in UV absorbance of humic acids, as compared to ozone alone. Fe/MgO was the most efficient catalyst in degradation humic acids in the presence of ozone. GPC (gel permeation chromatography) showed that humic acids with high molecular weight could be severely decomposed into organic compounds with low molecular weight by the Fe/MgO catalyst, indicating that humic acids could be catalytically decomposed.     

NAD+ hydrogenation on Au electrode deposited on modified glassy carbon

Gold nanoparticles(AuNP) were electrodeposited on a glassy carbon(GC) which was electrochemically modified by potentiodynamic cyclic polarization in acidic medium. The AuNP deposits were characterized by scanning electron microscopy, cyclic voltammetry, chronoamperometry and linear sweep voltammetry. Results of these studies showed that very small sized AuNP are deposited with significantly high particle density which is attributed to the surface modification of GC. The resulted AuNP/GC electrode showed high catalytic activity for electrochemical reduction of NAD⁺ to NADH, indicating its potential for electrocatalytic applications.