摘要
采用共沉淀法制备了MgO、CaO改性CuO-ZnO-Al2O3催化剂,通过XRD、N2物理吸附-脱附、TG-DTG、H2-TPR、CO2-TPD等表征手段,探讨助剂MgO、CaO添加对催化剂前体物相组成及催化剂微观结构的影响,考察了CO2加氢制备甲醇反应中MgO、CaO改性CuO-ZnO-Al2O3催化剂的性能。结果表明,CaO改性催化剂前体中形成的锌孔雀石相(Cu,Zn)2CO3(OH)2、绿铜锌矿相(Zn,Cu)5(CO3)2(OH)6,促进了催化剂中Cu-Zn协同活性位数量增加,同时助剂CaO的添加降低了催化剂中CuO和ZnO的晶粒度,增大了催化剂比表面积,改善了铜组分的表面分散度,有利于催化剂活性提高;MgO改性催化剂前体生成了绿铜锌矿相(Zn,Cu)5(CO3)2(OH)6,但没有锌孔雀石相(Cu,Zn)2CO3(OH)2生成,焙烧后催化剂中Cu-Zn协同作用较弱,此外MgO改性后催化剂比表面积减小,催化反应活性降低。MgO、CaO作为碱性助剂,调变了催化剂表面的碱强度和碱中心浓度,CaO改性催化剂的表面碱强度大于MgO改性催化剂,与CaO、MgO的碱性强度顺序一致,即CaO>MgO。
CuO-ZnO-Al2O3 was modified by co-precipitation,using MgO,CaO as promoters. The effects of MgO,CaO on phase composition and catalyst structure were illuminated by using N2 adsorption-desorption,TG-DTG,XRD,H2-TPR and CO2-TPD techniques. The catalysts were tested in the synthesis of methanol from CO2 hydrogenation in a fixed-bed reactor. It indicated that the addition of CaO favored the formation of aurichalcite （Zn,Cu）5（CO3）2（OH）6 and malachite zinc （Cu,Zn）2CO3（OH）2 in the precursor of the catalyst. The more （Zn,Cu）5（CO3）2（OH）6 or （Cu,Zn）2CO3（OH）2 precursor possessed,more synergy,lower reduction temperature after calcination it exhibited,which improved the catalytic performance of catalyst modified by CaO. The promoter of MgO did not benefit the formation of aurichalcite （Zn,Cu）5（CO3）2（OH）6 and malachite zinc （Cu,Zn）2CO3（OH）2,which led to less active catalyst due to the weak synergetic effect between Cu and ZnO. On the other hand,the formation of MgO-CuO solid solutions reduced the activity of the catalyst,although the crystallite size of CuO,ZnO was decreased and the dispersion of Cu on the surface was enhanced. It was also found that the intensity and amount of basic sites on the catalyst surface were modulated by the promoter of MgO,CaO. The CaO-modified CuO-ZnO-Al2O3 catalyst possessed stronger basic sites than that of MgO-modified,which was accordance with the basic strength order of CaO and MgO.
出处
《化工进展》
EI
CAS
CSCD
北大核心
2014年第11期2963-2969,共7页
Chemical Industry and Engineering Progress
基金
国家科技支撑计划(2011 BAC01B03)
国家自然科学基金(51304099)
云南省应用基础研究计划(2013FZ035)
昆明理工大学分析测试基金(2010213)项目
