多级孔二氧化硅负载铜催化剂制备及甲醇脱氢性能

Preparation and catalytic performance of hierarchical porous silica-supportedcopper catalysts for dehydrogenation of methanol to methyl formate

甲酸甲酯是一种重要的煤化工下游化学品,甲醇脱氢制甲酸甲酯主要使用铜基催化剂,金属铜易发生团聚、烧结是限制催化剂性能的关键因素。通过水热合成法制备有序多级孔氧化硅载体(HPS-x),采用蒸氨法和浸渍法分别制得Cu/HPS-x(x=100、130和160)和Cu/HPS-130-W催化剂,考察不同水热温度对催化剂在甲醇脱氢制甲酸甲酯的催化性能的影响,催化剂活性顺序为:Cu/HPS-130>Cu/HPS-160>Cu/HPS-100>Cu/HPS-130-W。表征结果显示,水热温度对HPS载体的织构性质有显著影响,HPS-100以微孔为主,介孔较少,HPS-160比表面积较低,HPS-130载体有适宜孔径分布的有序微介孔结构,能有效促进Cu粒子分散,防止活性组分团聚,进而提高催化剂活性。采用蒸氨法制备的Cu/HPS-130催化剂在0.2 MPa、300℃反应条件下,甲醇转化率和MF选择性分别达38.7%和79.8%,明显优于浸渍法制备的Cu/HPS-130-W催化剂。结果表明蒸氨法比浸渍法更有利于活性组分的分散,载体和金属间相互作用更强,避免活性组分的团聚和剥离。

Methyl formate is an important downstream product in coal chemical industry,which is mainly produced employing copper catalyst for methanol dehydrogenation.However,the agglomeration and sintering of copper are the key factors limiting the catalyst performance.A series of ordered hierarchical porous silica(HPS)presenting both mesopores and micropores were fabricated at different hydrothermal temperatures and used for preparing supported copper catalysts with ammonia evaporation and impregnation methods.Dehydrogenation of methanol to methyl formate(MF)over Cu/HPS catalysts was investigated and found that the catalyst activity decreased in the order of Cu/HPS-130>Cu/HPS-160>Cu/HPS-100>Cu/HPS-130-W.The characterization results show that the texture properties of HPS is heavily affected by the hydrothermal temperatures.The HPS-130 support shows more ordered hierarchical structure with appropriate pore size distribution compared with HPS-100 and HPS-160,which can promote the dispersion of Cu particles and prevent agglomeration and sintering of active copper species during the reaction.Moreover,the Cu/HPS-130 catalyst by the ammonia evaporation method exhibites the optimal catalytic performance with methanol conversion of 38.7%and MF selectivity of 79.8%under 0.2 MPa with 300℃,significantly superior to Cu/HPS-130-W prepared through impregnation method.The excellent catalytic performance of Cu/HPS-130 can be attributed to the formation of Cu-O-Si species,derived from the strong interaction between surface silica and copper precursor in the process of ammonia evaporation approach,which greatly inhibiteds the stripping of copper particles on the Cu/HPS catalysts.