负载型铼催化剂体系与甲醇选择氧化性能的关系

Abstract

[中文摘要]以铼酸铵为前驱体，制备了氧化物负载型铼催化剂并研究其甲醇选择氧化反应的催化性能．结果表明，Fe2O3和V2O5 等氧化物负载型铼催化剂表现出很高的甲醇选择氧化制备二甲氧基甲烷的催化性能，选择性可达 90％～94％（摩尔分数）．选择氧化反应活性与铼担载量有关．在α－Fe2O3担载的铼催化剂中，以担载质量分数为 1％～3％铼的催化剂活性最高［450 mmol／（h·g Re）]，而高于 3％的铼担载量，单位铼催化活性逐渐下降．XRD，XPS和脉冲反应等结果表明，铼酸铰负载于α-Fe2O3 载体上，并于He气氛中焙烧后，所得表面铼物种与担载量有关，当低于单层担载量时以 Re6+占主导，而高于单层担载量时则 Re6+与 Re4+物种共存．[英文摘要] Supported Re catalysts were prepared by impregnation of ammonium perrhenate precursor on oxide supports, followed by calcination at 673 K in He steam. Iron-oxides and V2O5 supported Re catalysts showed a higher activity and selectivity for the catalytic methanol oxidation to dimethoxymethane [3CH3OH + (1/2)O2 CH2(OCH3)2 + 2H2O]. The selectivity was as high as 90%-94% (molar fraction) at 513 K. The highest reaction rate of 450 mmol·h-1·g-1 Re on α-Fe2O3 supported Re catalysts was achieved with the Re loading weight of 2%(mass fraction).The reaction rate gradually decreased with the inerease of Re loading weight.Caleination of ammonium perrhenate alone at 673 K in He gave monooelinie ReO2 as a main produet.However,the application of the iron-oxide may prevent Re7+ from reducting to Re4+ during the calcination at 673 K in He in the case of proper Re loading weight probably through the interaetion of ammonium perrhenate with the supports,leading to the growth of Re6+ on the catalyst surface.Above the monolayer loading weight of ReO3,there was coexistence of Re6+ and Re4+ on the catalyst surface.A redox mechanism between Re6+ and Re4+ species on the catalyst surface was proposed to be responsible for the high performance in the methanol selective oxidation to dimethoxymethane.