载体Al/Si比对Cu-ZnO-ZrO_2催化剂上CO_2加氢合成甲醇的影响

Influence of Al/Si Ratio of Catalyst Support on CO_2 Hydrogenation to Methanol Catalyzed by Cu-ZnO-ZrO_2

用直接合成法制备了不同铝硅物质的量比Al-SBA-15(β)(β=n(Al)/n(Si)=0,0.02,0.03,0.05)介孔分子筛,并采用浸渍法制备了金属负载量m=35%的CZZ/Al-SBA-15(β)负载型介孔催化剂,考察了Al/Si比对负载催化剂结构和性能的影响。采用N_2吸附-脱附、X射线衍射(XRD)、H_2程序升温还原(H_2-TPR)、CO_2吸附(CO_2-TPD)、NH3吸附(NH3-TPD)和透射电子显微镜(TEM)等手段对样品进行了表征,在固定床反应器上评价了其CO_2加氢合成甲醇的催化性能。实验结果表明,CZZ/Al-SBA-15(β)具有介孔结构,Al的引入不但增加了载体表面酸性位点,同时还提高了催化剂表面铜分散度(DCu%)和铜比表面积(SCu)以及促进了Cu^+-O-Zn活性位的形成,从而大大提高了催化剂的活性。其中CZZ/Al-SBA-15(0.03)催化剂的甲醇选择性达到26%,与不掺铝的CZZ/Al-SBA-15(0)催化剂相比,甲醇选择性提高了11%,但随着掺Al量的继续增加,酸性太强,CO_2吸附能力下降,活性反而降低。

A series of mesoporous aluminosilicate supports(Al SBA15(β),β=n(Al)/n(Si)=0,0.02,0.03,0.05)with diverse Al/Si molar ratios were prepared,and CuO ZnO ZrO nanoparticles were loaded on Al SBA15supports by a simple impregnation method(CZZ/Al SBA15(β),m=35%).The effect of Al/Si ratios of mesoporous support on structure and properties of the supported catalysts were investigated by employing N2adsorption desorption,X ray diffraction(XRD),transmission electron microscopy(TEM),H2temperature programmed reduction(H2TPR),CO2temperature programmed desorption(CO2TPD)and N2O titration technique(N2O RFC)to determine the textual structure and physicochemical properties of CZZ/Al SBA15(β)samples.The catalytic activities of these catalysts for CO2hydrogenation to methanol were determined in a fixed bed reactor.Experimental results showed that CZZ/Al SBA15(β)has a mesoporous structure,the addition of Al not only increased the surface acid sites of the supports,but also improved the DCu%,SCu of the samples and promoted the formation of Cu+O Zn active sites.CZZ/Al SBA15(0.03)catalyst showed a high methanol selectivity(26%),which increases by11%compared with non doped aluminum CZZ/Al SBA15(0)catalyst.However,the overdoping of Al element results in an unduly high acidity of support,thus attenuating CO2absorption and catalytic activity.