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首页> 外文期刊>Catalysis science & technology >Tuning the metathesis performance of a molybdenum oxide-based catalyst by silica support acidity modulation and high temperature pretreatment
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Tuning the metathesis performance of a molybdenum oxide-based catalyst by silica support acidity modulation and high temperature pretreatment

机译：调整二氧化硅基于氧化钼的催化剂的酸度调节和高温预处理的分解性能

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摘要

Molybdenum oxide-based catalysts containing 5 wt% of Mo obtained by simple impregnation of a silica mesoporous support were studied in the olefin metathesis reaction at 50 °C. The effect of support modification as well as high temperature pretreatment of the catalysts before metathesis was evaluated. The acid properties of the base mesoporous silica SBA-1 support with a cubic pore structure were tuned by Al-doping post-preparation procedures using ammonium hexafluoro-aluminate to control the Si/Al ratio. The possibility to control the acidity as well as the difference in the structure of molybdenum oxide sites is discussed. Correlation between the acidity of the supports and the catalytic performance was found. Al-Doping improves the specific activity and propylene conversion. However, an increase in acidity has a negative effect on the selectivity to metathesis products. Furthermore, the effect of high temperature pretreatment of the catalysts on their metathesis performance was investigated. Molybdenum oxide based catalysts supported on pure SBA-1 were pretreated in a flow of inert gas, hydrogen, carbon monoxide and hydrocarbons (ethane and propane) at 650 °C. It has been clearly shown that short pretreatment in carbon monoxide and hydrocarbon atmospheres improves significantly the catalytic performance in comparison with hydrogen pretreatment or conventional pretreatment in inert atmospheres. Based on DFT calculations, the H-assisted mechanism for the formation of active Mo alkylidene species from silica–alumina-supported Mo(iv) oxo species with participation of neighboring Brønsted acid sites is proposed.
机译：在50°C下的烯烃序列化反应中研究了基于氧化钼的基于氧化物的催化剂，这些催化剂含有5 wt％的MO。评估了分解前的催化剂的支撑修饰以及高温预处理的影响。使用Hexafluoro-铝酸酯掺杂后，通过Al掺杂后进行了Al掺杂后，对基础介孔SBA-1载体的酸性质进行了调整，以控制Si/Al比率。讨论了控制酸度以及氧化钼位点结构差异的可能性。发现载体的酸度与催化性能之间的相关性。 Al兴奋剂改善了特定活性和丙烯转化率。然而，酸度的增加对元理解产物的选择性有负面影响。此外，研究了催化剂高温预处理对其离心性性能的影响。在650°C下，将支持纯SBA-1支持的基于纯SBA-1的钼催化剂预处理以惰性气体，氢，一氧化碳和丙烷）（乙烷和丙烷）进行预处理。已经清楚地表明，与液体预处理或惰性大气中的常规预处理相比，一氧化碳和碳氢化合物的简短预处理可显着改善催化性能。基于DFT计算，提出了二氧化硅 - 铝支持的MO（IV）氧氧化物的活性Mo烷基二烯种类的H辅助机制，并提出了邻近的Brønsted酸位点的参与。

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