Search

Abstract: Mechanism and kinetics of catalytic process for a new low-temperature methanol synthesis on Cu/ZnO catalysts from syngas (CO/CO2/H2) using catalytically active alcohol promoters were investigated by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Two intermediate species, adsorbed formate species and alkyl formate species, were formed in this synthesis process. The adsorbed formate species easily reacted with ethanol or 2-propanol at 443K and atmospheric pressure, and the reaction rate with 2-propanol was faster than that with ethanol. Alkyl formate was readily reduced to form methanol at 443K and 1.0MPa, and the hydrogenation rate of 2-propyl formate was found to be quicker than that of ethyl formate. As a promoter, 2-propanol exhibited a higher activity than ethanol in the reaction of the low-temperature methanol synthesis. [Copyright &y& Elsevier]

Abstract: In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to study the reaction mechanism of the formate adsorbed species with ethanol to form the ethyl formate on Cu/ZnO catalyst surface in a novel low-temperature methanol synthesis process. The results indicate that the formate adsorbed species were firstly formed by CO/CO2/H2 adsorbed on Cu/ZnO catalyst, followed by rapid reaction with ethanol to form ethyl formate. It was found that the species reacted with formate adsorbed species were ethanol in gas phase rather than adsorbed ethoxy species. The reaction of the adsorbed formate species with ethanol on Cu/ZnO catalyst surface proceeded according to Rideal-type mechanism, not Langmuir–Hinshelwood mechanism. [Copyright &y& Elsevier]

Abstract: In situ diffuse reflectance infrared Fourier-transform spectroscopy was used to clarify the reaction mechanism of a new methanol synthesis method on a Cu/ZnO catalyst at low temperature such as 423K from syngas containing CO2 and H2O using a 2-propanol promoter. The formate species was formed by exposing Cu/ZnO catalyst to syngas, and it easily reacted with 2-propanol to form a 2-propyl formate species at low temperature. 2-Propyl formate was then quickly reduced to form methanol and 2-propanol. The Cu/ZnO catalyst was active for all these steps while catalytically cycled 2-propanol realized a low-temperature route. [Copyright &y& Elsevier]

In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to study the reaction mechanism of a new methanol synthesis method on Cu/ZnO at low temperatures from syngas (CO/CO2/H2) using ethanol promoter. The adsorbed formate species were formed by exposing Cu/ZnO catalysts to syngas (CO/CO2/H2), and it reacted easily with ethanol in the gas phase to form ethyl formate in two states of species, gas phase and physisorbed, at low temperatures. Ethyl formate was the reactive intermediate, and it was reduced easily by hydrogen atoms on Cu to form gas-phase methanol. The reaction temperature was significantly decreased due to the catalytic action of ethanol and a new reaction route. In order to accelerate this reaction, a large amount of ethanol must be introduced into the reaction system. When there was no ethanol or little ethanol in the reaction system, this reaction was difficult to complete at a temperature as low as 443 K. [Copyright &y& Elsevier]

Abstract: A series of the as-burnt and the burnt Cu/ZnO catalysts were prepared by a sol–gel auto-combustion method using metal nitrates with the mole ratio of Cu/Zn=1/1 (noted as M, M=Cu+Zn) and citric acid (noted as CA). When the xerogels were burnt in the argon atmosphere, H2 and CH4 which were came from the decomposition of the citric acid, were the reducing agents and were used in the redox process for synthesizing metallic Cu from Cu2+ in the chelated compound. The XRD patterns revealed that all the as-burnt catalysts with different M/CA molar ratios were converted into pure Cu and ZnO species. TPR analysis of the as-burnt catalyst illustrated that almost no hydrogen was consumed. It proved that Cu2+ in the chelated compound was absolutely reduced to metallic Cu in the as-burnt catalyst. The effects of M/CA molar ratio on the properties of catalysts were studied by TG-DTA, FT-IR, Raman spectrum, XRD, SEM-EDS, BET, and N2O chemisorption techniques. The activity of the as-burnt catalysts without reduction was investigated for low-temperature methanol synthesis from syngas containing CO2 using ethanol as a promoter at 443K and 5.0MPa for 12h. The total carbon conversion increased with increasing the content of citric acid and reached a maximum for the as-burnt Cu/ZnO catalyst C0.8 with M/CA=1/0.8, and then decreased. The variation trend was in accordance with that of the copper (Cu0) surface area. Comparing with the burnt catalyst C0.8-air after reduction, the methanol selectivity of the as-burnt Cu/ZnO catalyst was much lower owing to lower hydrogenation activity of the ethyl formate. The as-burnt catalyst C0.8 was also used in continuous low-temperature methanol synthesis at 443K and 5.0MPa for 40h. The total carbon conversion was stable after 15h and no obvious deactivation during 40h reaction, but the methanol selectivity was still not high. [Copyright &y& Elsevier]

The Cu/ZnO catalyst prepared by urea hydrolysis method was investigated for low-temperature methanol synthesis from syngas containing CO 2 . Concurrently, the activity of the conventional Cu/ZnO catalyst prepared by co-precipitation method was also compared. The effects of precipitation temperature, urea content, stirring speed and the introduction of Al on the catalytic performance of Cu/ZnO were deeply studied. It was found that the total carbon conversion of the Cu/ZnO catalyst prepared by urea hydrolysis method was increased to 45.0% from 32.8%, comparing with that of the catalyst prepared by co-precipitation method. The structure, BET surface area, surface morphology of the catalyst were characterized by XRD, BET, EDX and SEM. The catalyst prepared by urea method obtained higher BET surface area and larger metallic surface area of Cu than those of the co-precipitation method. The crystals sizes of Cu by urea method were smaller than those of co-precipitation method. Surface structure prepared by urea method had needle shape, and it could increase the surface area, different from the catalyst by co-precipitation method. Both the increased BET surface area of the catalysts and the enhanced metallic surface area of Cu 0 promoted the catalyst activity for the low-temperature methanol synthesis. The deactivation of the Cu-ZnO catalysts prepared by urea method was not observed in low-temperature methanol synthesis here. [ABSTRACT FROM AUTHOR]