Influence of pretreatment conditions on low-temperature CO oxidation over Au/MOx/Al2O3 catalysts

Composite oxide MO_x/Al₂O₃ supported gold catalysts for low-temperature CO oxidation were prepared and investigated. The presence of transition metal oxide was proved to be beneficial to the improvement of catalytic performance of Au/Al₂O₃ catalysts for low-temperature CO oxidation. Furthermore, the influence of various pretreatment conditions on Au/MO_x/Al₂O₃ catalysts was studied carefully. The image of TEM showed that gold catalyst with small gold particles only in the form of a fine dispersion exhibited highly catalytic activity. The XPS, Fourier transform infrared (FTIR) spectroscopy characterization results of Au/FeO_x/Al₂O₃ catalyst showed that gold catalysts having partially oxidized gold species have the best catalytic performance. One possible pathway for CO oxidation on Au/FeO_x/Al₂O₃ catalyst is that the CO adsorbed on gold particles reacts with adsorbed oxygen, which is possible to occur on oxygen vacancies on the support or at the metal–support interface.     

Solubility Behavior in Ternary Water-Salt Systems under Sub- and Supercritical Conditions

Summary.  Two main types of binary systems with distinctive solubility behavior under sub- and supercritical conditions were used to subdivide ternary water-salt systems into three classes. Characteristic features of solubility behavior and phase equilibria in ternary water-salt systems of each class at temperatures above 200°C are discussed on the basis of available experimental data and some conclusions obtained as a result of theoretical derivation of fluid and complete phase diagrams. Corresponding author. E-mail: Valyashko@IGIC.RAS.RU Received September 25, 2002; accepted (revised) November 28, 2002 Published online April 24, 2003 RID="a" ID="a" Dedicated to Prof. Dr. H. Gamsjaeger on the occasion of his 70^th birthday anniversary     

Kinetic model of CO oxidation on heterophase surface analyzed regarding COads spillover, I. Homotopic method. Effect of temperature and CO pressure

The homotopic method has been used to analyze the kinetic models of CO oxidation on two surface patches conjugated by CO_ads spillover. On each patch reaction proceeds via a three-stage mechanism but with different constants. The stability of steady-states solution has been studied. CO_ads spillover from one patch to another changes substantially the bifurcation picture of steady states and produces islands.     

Reactions of the Ru3(CO)10(μ-Ph2PCH2PPh2) cluster with enynes RCH=CHC≡CR (R is phenyl or ferrocenyl). Formation of indenone derivatives of triruthenium clusters

The thermal reaction of Ru₃(CO)₁₀(-Ph₂PCH₂PPh₂) (1) with enyne PhCH=CHCCPh afforded the trinuclear ruthenium clusters Ru₃(CO)₆{₃-P(Ph)CH₂PPh₂}{₃-C(Ph)=CHCC(Ph)(1,2-C₆H₄)C(=0)} (2), Ru₃(-H)(CO)₅{₃-P(Ph)CH₂PPh₂}{₃-C(Ph)=CHCC(Ph)(1,2-C₆H₄)C(—0)} (3), and Ru₃(CO)₆(-CO){₃-P(Ph)CH₂PPh₂}{₃-C(C=CPh₂)CH=C(H)Ph} (4) and also two isomers of Ru₃(CO)₅(-CO)(-Ph₂PCH₂PPh₂){₃-C₄Ph₂(CH=CHPh)₂} (5a and 5b). Clusters 2, 3, and 4 were characterized by IR spectroscopy, ¹H and ³¹P NMR spectroscopy, and X-ray diffraction analysis. The reaction of complex 1 with enyne FcCH=CHCCFc gave rise to the Ru₃(CO)₆{₃-P(Ph)CH₂PPh₂}{₃-C(Fc)=CHCC(Fc)(1,2-C₆H₄)C(=0)} (6) and Ru₃(-H)(CO)₅{₃-P(Ph)CH₂PPh₂}{₃-C(Fc)=CHCC(Fc)(1,2-C₆H₄)C(—0)} (7) clusters. According to the spectral data, the latter compounds are isostructural to complexes 2 and 3, respectively.     

FTIR study of CO adsorption on molybdena-alumina catalysts for surface characterization

CO adsorption at low temperature has been used to probe Lewis acid sites created upon dehydroxylation of γ-Al₂O₃ and reduction of Mo/Al₂O₃ catalysts, using Fourier Transform Infrared spectroscopy (FTIR). Carbon-monoxide adsorption on γ-Al₂O₃ and Mo/Al₂O₃ catalysts dehydroxylated and reduced at different temperatures was studied at 78 K by IR spectroscopy. However, our results indicate that there is an approximately linear correlation between the increase either of dehydroxylation or the extent of reduction of the catalysts and the increasing absorbance of CO due to CO adsorption on Lewis acid sites created upon dehydroxylation of γ-Al₂O₃ and reduction of Mo/Al₂O₃.     

Rh(I)-catalyzed Pauson-Khand reaction of 1-phenylsulfonyl-1,2-octadien-7-yne derivatives

The Rh(I)-catalyzed PKR of 1-phenylsulfonyl-1,2-octadien-7-ynes and their aza derivatives exclusively produced the corresponding 9-phenylsulfonylbicyclo[4.3.0]nona-1,6-dien-8-ones and no 4-(phenylsulfonylmethylidene)bicyclo[3.3.0]oct-1-en-3-ones could be detected. Thus, the ring-closing pattern was found to be the same as those of the previously reported 3-phenylsulfonyl-1,2-octadien-7-yne derivatives. However, the formation of 4-(phenylsulfonylmethylidene)-7-oxabicyclo[3.3.0]oct-1-en-3-ones was observed as a minor product when the 5-oxa congeners were used. In addition, a larger ring-sized product, 10-phenylsulfonyl-5-azabicyclo[5.3.0]deca-1,7-dien-9-one derivative, was obtained from the 6-aza derivative of 1-phenylsulfonyl-1,2-nonadien-8-yne.     

Hydrogen-induced metal-oxide interaction studied on noble metal model catalysts

Summary The effect of hydrogen reduction on the structure and catalytic properties of “thin film”and “inverse”model systems for supported metal catalysts is discussed. Thin film model catalysts were obtained by epitaxial growth of Pt and Rh nanoparticles on NaCl(001), which were coated with amorphous or crystalline supports of alumina, silica, titania, ceria and vanadia. Structural and morphological changes upon hydrogen reduction between 473 and 973 K were examined by high resolution electron microscopy. Metal-oxide interaction sets in at a specific reduction temperature and is characterized by an initial “wetting”stage, followed by alloy formation at increasing temperature, in the order VO_x< TiO_x< SiO₂< CeO_x< Al₂O₃. “Inverse”model systems were prepared by deposition of oxides on a metal substrate, e.g. VO_x/Rh and VO_x/Pd. Reduction of inverse systems at elevated temperature induces subsurface alloy formation. In contrast to common bimetallic surfaces, the stable subsurface alloys of V/Rh and V/Pd have a purely noble metal-terminated surface, with V positioned in near-surface layers. The uniform composition of the metallic surface layer excludes catalytic ensemble effects in favor of ligand effects. Activity and selectivity, e.g. for CO and CO₂methanation and for partial oxidation of ethene, are mainly controlled by the temperature of annealing or reduction. Reduction above 573 K turned out to be beneficial for the catalytic activity of the subsurface alloys, but not for the corresponding thin film systems which tend to deactivate viaparticle encapsulation.</o:p>     

An IR Study on Adsorption of CO and NO on Copper Ion-exchanged Zeolite Beta

Thee adsorption of CO and NO on copper ion-exchanged zeolite Beta was investigated using IR method.It was found that the thermalvacuum pretreatment procedure could result in the reduction of Cu2 ions in zeolite Beta.The adsorption of CO on Cu sites in zeolite Beta closely follows Langmuir isotherm.Another Cu species may form during the reaction between water and CO.The catalytic decomposition of NO on the zeolite was observed at room temperature,indicating that the decomposition reaction may occur between two coordinated NO ligands of the same dinitrosyhc complex.Furthermore,the appearance of two series of NO adsorption bands reveals that copper ions existing at different cation sites may have different effect on the adsorption and decomposition of NO molecules.     

Calorimetric study of room temperature adsorption of N2O and CO on Cu(II)-exchanged ZSM5 zeolites

Copper ion-exchanged ZSM5 zeolites have been prepared with different cooper loadings from under- to over-exchanged levels. The adsorptions of N₂O and CO at 303 K have been studied using calorimetric method and infrared spectroscopy. The samples were additionally characterised by ammonia adsorption at 423 K. The active sites for both N₂O and CO are Cu(I) ions, which were formed as a result of pre-treatment in vacuum at 673 K.

Room temperature adsorption of nitrous oxide at low equilibrium pressures (up to 66.7 Pa) resulted in small amounts of chemisorbed N₂O (<0.2 molecule per one Cu ion). Differential heats of N₂O adsorption between 80 and 30 kJ/mol were obtained. Differential heats of CO adsorption between 140 and 40 kJ/mol were obtained. The obtained amounts of chemisorbed species in the investigated systems and the values of differential heats of both nitrous oxide and carbon monoxide demonstrate the dependence on the copper content.     

Conventional processes and membrane technology for carbon dioxide removal from natural gas:A review

Membrane technology is becoming more important for CO 2 separation from natural gas in the new era due to its process simplicity,relative ease of operation and control,compact,and easy to scale up as compared with conventional processes.Conventional processes such as absorption and adsorption for CO 2 separation from natural gas are generally more energy demanding and costly for both operation and maintenance.Polymeric membranes are the current commercial membranes used for CO 2 separation from natural gas.However,polymeric membranes possess drawbacks such as low permeability and selectivity,plasticization at high temperatures,as well as insufficient thermal and chemical stability.The shortcomings of commercial polymeric membranes have motivated researchers to opt for other alternatives,especially inorganic membranes due to their higher thermal stability,good chemical resistance to solvents,high mechanical strength and long lifetime.Surface modifications can be utilized in inorganic membranes to further enhance the selectivity,permeability or catalytic activities of the membrane.This paper is to provide a comprehensive review on gas separation,comparing membrane technology with other conventional methods of recovering CO 2 from natural gas,challenges of current commercial polymeric membranes and inorganic membranes for CO 2 removal and membrane surface modification for improved selectivity.