材料期刊网

采用等容浸渍法,制备了t-ZrO2,m-ZrO2,CeO2和CexZr1-xO(x=0.05 ～0.8)负载RuOx催化剂,研究了载体对RuOx物种的结构及其催化甲醇选择氧化反应性能的影响.通过XRD,Raman,XPS和H2-TPR等手段对这些催化剂进行表征,发现当Ru表面密度为0.23 ～0.43Ru·nm-2时,RuOx物种以高分散形式存在,该结构含有Ru=O键以及与载体之间的Ru-O-S(S表示载体阳离子)键,且其Ru 3d5/2结合能为281.6 eV.这些结果表明高分散RuOx物种以RuO42-结构形式存在.H2-TPR结果表明,CeO2和CexZr1-xO(x=0.05～0.8)载体相比于t-ZrO2和m-ZrO2载体具有更加优异的氧化还原性能.RuOx/CeO2催化甲醇选择氧化反应活性显著优于RuOx/t-ZrO2和RuOx/m-ZrO2催化剂.随Ce含量增加,RuOx/CexZr1-xO(x=0～1.0)催化反应活性逐渐增大,反映出氧化还原性载体能够促进高分散RuOx催化剂的活性.同时,甲酸甲酯产物的选择性也随之升高,反应温度为100℃时,在～20％甲醇转化率下,甲酸甲酯选择性可达81.5％.

RuOx catalysts supported on t-ZrO2,m-ZrO2,CeO2 and CexZr1-xO (x =0.05 ～0.8) were prepared by an incipient wetness impregnation method,and examined for selective oxidation of methanol to methyl formate (MF).These catalysts were characterized by XRD,Raman,XPS,and H2-TPR,showing that the RuOx species were highly dispersed on their support surfaces at the Ru surface densities of 0.23 ～0.43 Ru ·nm-2 These dispersed RuOx species possessed Ru =O and Ru-O-S (S denotes Ce4+ or Zr4 + from the supports) bonds in the RuO42-structures,as evidenced from their characteristic Raman bands at 972 ～992 cm-1 and 702 ～712 cm-1 respectively,and the Ru 3d5/2 binding energy at 281.6 eV.CeO2 and CexZr1-xO (x =0.05 ～0.8) were more reducible than t-ZrO2 and m-ZrO2 from the H2-TPR results.The activities of RuOx/CexZr1-xO (x =0 ～ 1.0) increased gradually with increasing their Ce contents,and RuOx/CeO2 were superior to RuOx/t-ZrO2 and RuOx/m-ZrO2 catalysts in the selective oxidation of methanol at 100 ℃.Such change in the activities for these catalysts is consistent with the reducibility of the RuOx species and the underlying supports,clearly showing the promoting effect of the redox properties of the supports on the activities of the RuO42 species.The MF selectivities for these catalysts simultaneously increased with increasing their Ce contents,and a highest selectivity of 81.5 ％ was achieved on RuOx/ Ce0.8Zr0.2O at a methanol conversion of ～20％.