The effects of calcination temperature and MoO3 loading on the syngas methanation performance of MoO3/γ-Al2O3 catalyst prepared by the incipient-wetness impregnation method were studied. Mo–Al/25 catalyst (∼4.04 Mo/nm2) calcined at 600 °C reached maximum activity with 46.45% CO conversion. All of the experimental results demonstrated that the saturated monolayer coverage of MoO3 over a γ-Al2O3 support was closet to 25 wt.% MoO3. It was discovered that tetrahedrally coordinated Mo6+ (T), instead of octahedrally coordinated Mo6+ (O), is the active catalytic precursor in its oxidised state. Additionally, it was also confirmed that the presence of crystalline MoO3 and Al2(MoO4)3 species depended on not only the MoO3 loading but also the calcination temperature.

Effects of MoO3 loading and calcination temperature on the activity of the sulphur-resistant methanation catalyst MoO3/γ-Al2O3

CO methanation over supported Mo catalysts in the presence of H2S

A series of MoO3/Al2O3 catalysts with different amounts (molar ratio of CA/Mo = 0, 1, 1.5, and 2) of citric acid (CA) prepared by simultaneous impregnation were evaluated for sulfur-resistant methanation. Based on the evaluation results, catalytic activity increased accompanied with the rise of citric acid amount. Combine with the analysis of N2-physisorption, XRD, H2-TPR, XPS, and TEM, the catalyst saturated loading capacity improved, resulting in increasing dispersion of Mo species on Al2O3 surface clearly. According to H2-TPR result, the Mo oxide precursors can be more easily sulfureted when citric acid is added. Moreover, based on the Raman analysis, increasingly tetrahedrally coordinated Mo6+ species with high methanation performance are generated after citric acid treatment. These factors probably together accelerate MoO3/Al2O3 catalytic activity growth for methanation.

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Effect of Citric Acid on MoO3/Al2O3 Catalysts for Sulfur-Resistant Methanation

Thermodynamic analysis of the correlation of H2S and COS has been carried out at the temperature range of 400–650 °C at which high temperature desulfurization of coal gas is usually performed. The correlation of the two sulfur species is mainly through the reaction H2S+CO→COS+H2. Simulated coal gas with the following composition CO 32.69%, H2 39.58%, CO2 18.27%, N2 8.92% and H2S 0.47% was used in this study, and the equilibrium concentrations of the two species at different temperatures were calculated. The results of Fe-based sorbents during sulfidation were compared with calculations. It is concluded that the above reaction may reach equilibrium concentration in the presence of the Fe-based sorbents, which means the Fe-based sorbents may effectively catalyze the reaction between H2S and CO. Because of the correlation of the two sulfur species, both can be effectively removed at high temperatures simultaneously, offering high temperature desulfurization some advantages over low temperature desulfurization processes.

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Correlation of H2S and COS in the hot coal gas stream and its importance for high temperature desulfurization

The first step in the two-step CO-catalyzed conversion of H{sub 2}S to H{sub 2} and sulfur has been studied in order to establish the optimal experimental conditions for the reaction. Without a catalyst, H{sub 2}S conversions of the order of only 1--2% could be achieved. NiS on alumina proved to be an efficient catalyst, and at 267 C, H{sub 2}S conversions reached 52% or 100% of the thermodynamic limit. Small amounts of CO{sub 2} and CS{sub 2} have also been detected among the products. In comparative experiments using CoS on alumina as the catalyst, up to 67% conversion, representing 100% of the thermodynamic equilibrium H{sub 2} yield, could be achieved at a substantially lower temperature, 177 C. Furthermore, formation of CO{sub 2} and CS{sub 2} was found to be negligible (<1%) at this low temperature, eliminating the need for the suppression of the COS disproportionation reaction.

John Goral

Papers

Molybdenum disulfide-catalyzed methanation of carbon monoxide with hydrogen sulfide

MoS2-catalyzed methanation of CO with H2S*1