Deng Jingfa

A novel process for preparation of a Cu/ZnO/Al2O3 ultrafine catalyst for methanol synthesis from CO2 + H2: comparison of various preparation methods

Abstract The effect of preparation methods on the structure and catalytic behavior of Cu/ZnO/Al 2 O 3 catalysts for methanol synthesis from hydrogenation of carbon dioxide has been studied. The Cu/ZnO/Al 2 O 3 ultrafine catalysts obtained by a novel gel-coprecipitation process exhibited higher catalytic activity for the synthesis of methanol from CO 2 + H 2 . The results showed that isomorphous substitution took place between copper and zinc in the precipitates prepared by the novel process. Preparation methods have a significant influence on the structure of the catalyst and catalytic activity for methanol synthesis from hydrogenation of carbon dioxide.

The oxidation of methanol on electrolytic silver catalyst

The oxidation of methanol on the surface of electrolytic silver catalyst has been investigated with Temperature-Programmed Reaction Spectroscopy (TPRS). It has been found that on a clean surface of electrolytic silver no adsorption of CH3OH or H2 occurred except the adsorption of small amounts of H2O or CO2, but the ability of silver to chemisorb the gases mentioned above was greatly enhanced by oxygen preadsorbed on the surface. In the reaction of methanol with preadsorbed oxygen-18, three distinct groups of product were observed at 400, 500 ± 20, and 620 K, respectively. At room temperature, the selective oxidation of methanol led to adsorbed surface species CH3O(a). During desorption, CH3O(a) decomposed and HCHO, CO18O, and H218O were evolved simultaneously at 400 K as the first group of products. At high oxygen coverage, surface oxygen interacted with the carbon atom of CH3O(a) to form another type of stable surface intermediate H3CO18O(a), which decomposed with a pseudo-second-order kinetics at 600 K, yielding only HCHO and H218O with a stoichiometric ratio of 2:1. The evolution of the second group of products CH3OH, CO18O, and H218O at 500 K was rate-limited by desorption of the products.

TDS and XPS studies of the adsorption of O2 on electrolytic silver

Abstract Thermal desorption spectroscopy (TDS) and X-ray photoelectron spectroscopy (XPS) have been employed to study the adsorption of oxygen on electrolytic silver. In the pressure range of 1−10 −8 Torr, several kinds of oxygen species have been observed on the surface: (A) Adsorbed molecular oxygen ( E d = 101 kJ/mol, v = 4 × 10 11 s −1 ), (B) surface bound atomic oxygen ( E d = 134 kJ/mol, v = 4.7 × 10 13 s −1 ) and (C) sub-surface atomic oxygen. Results of XPS show that the binding energies of 1s orbitals of these species of oxygen on silver are 528.3, 529.7, 520.2 and 532.2 eV. Two bands centered at 2.8–3.0 and 9.0 eV below the Fermi level appear on the difference spectrum of the valence band which again indicates that both atomic and molecular oxygen exist on the surface of silver.

A new process for preparing dialdehydes by catalytic oxidation of cyclic olefins with aqueous hydrogen peroxide

Abstract Dialdehydes were prepared by the reaction between cyclic olefins and aqueous hydrogen peroxide catalyzed by tungstic acid. Glutaraldehyde and adipaldegyde were synthesized by this method with good yield. Several different conditions were tested.

The catalytic oxidation of CO on superconductor Ba2YCu3O7–8

The measurements of MS-TPD, TPRS, the electrical conductivity and kinetics on Ba2YCu3O7-8 show that the catalytic activity of CO oxidation is closely related to properties such as the amounts and sites of oxygen, and electrical conductivity. Based on the experimental results a reaction mechanism has been suggested.

Acidic properties of ZSM-5 zeolite and conversion of ethanol to diethyl ether

Abstract In situ infrared spectroscopy, adsorption isotherms, temperature-programmed desorption and X-ray photoelectron spectroscopy have been used to investigate the acidic and surface properties of HZSM-5 and phosphorus-modified ZSM-5 zeolites. The catalytic conversion of ethanol to diethyl ether has been studied. The yield of diethyl ether and the optimum reaction temperature depend on the total acidity and acid strength of the samples, respectively.

Promoting effects of Re and Cs on silver catalyst in ethylene epoxidation

The study of ethylene epoxidation on promoted silver catalysts has been an active field in recent years. Alkali metals, boron, thallium, antimony, etc., are often incorporated into practical Ag/[alpha]-Al[sub 2]O[sub 3] catalysts in order to improve the selectivity of ethylene oxide. In recent work, it has been found that both Re and Cs added to Ag/[alpha]-Al[sub 2]O[sub 3] can increase the selectivity greatly, but no further information about the function of promoters was given. The authors have recently reported that the Re-promoted electrolytic silver catalyst appears to have a higher selectivity for ethylene epoxidation, and have investigated the function of Re. Most investigators had been concerned with the nature of promoters in ethylene epoxidation. The promoting effects of alkali and alkaline earth metal compounds were studied by Lambert and co-workers, and Campbell with surface science techniques. Most of these experiments were carried out on single Ag crystals. The present work describes the promoting effects of adding Re and Cs to electrolytic silver, on ethylene epoxidation and the adsorption of oxygen on the sample surface. The nature of Re and Cs promoters is also reported. 21 refs., 3 figs., 1 tab.

Rhenium as a promoter for ethylene epoxidation

Abstract The reaction of ethylene epoxidation was studied over electrolytic silver catalysts with an additive of rhenium in the range 1.9–6.5 ppm, and the effect of the rhenium promoter was also investigated by studying the adsorption of oxygen on the surface of a Ag-Re catalyst containing 4.15 ppm rhenium. It was found that both the conversion of ethylene and the selectivity of ethene oxide could be improved by the use of a rhenium-modified silver catalyst. The temperature desorption spectra of oxygen showed two adsorbed states, which were different from those on other silver samples. The effect of rhenium was to weaken the silver-oxygen bond, and to reduce the electron density of the adsorbed oxygen, which could be the reason for the enhancement of selectivity of ethene oxide.

Hreels of methanol oxidation on polycrystalline silver: Spectroscopic evidence for adsorbed intermediates in the conversion of methoxide to formaldehyde and water

The adsorption and the decomposition of methanol on an oxygen precovered polycrystalline silver surface were characterized by high resolution electron energy loss spectroscopy. A stable methoxy species and subsequently two new intermediates related to the decomposition of methoxy have been isolated and identified by temperature profiled ELS.

Study of the promoting effects in ethylene epoxidation

The promoting effects in the ethylene epoxidation reaction on an electrolytic silver surface by chemical modification with Ba and Cs compounds were studied. Ba increases the conversion of ethylene and decreases a little of the selectivity to ethylene oxide. In contrast, Cs increases the selectivity to EO at the expense of conversion of ethylene. Changes in the work function and the TPD of oxygen adsorption on modified Ag surfaces were measured. Promoting effects are explained by the idea that atomic oxygen is the crucial species for epoxidation.