稀土元素改性CO_(2)加氢制甲醇催化剂的研究进展

Research progress on catalysts modified by rare earth elements for CO_(2) hydrogenation to methanol

化石燃料对人类社会具有重要作用,然而CO_(2)大量排放对全球气候产生了负面影响。CO_(2)加氢制甲醇不仅能够有效降低大气中CO_(2)浓度,还提供了高附加值化学品。非贵金属(Cu)基、贵金属(Pd)基和双金属氧化物等一系列催化剂已经被运用于CO_(2)加氢制甲醇,然而传统Cu基催化剂存在反应条件苛刻、活性位点易烧结和团聚的问题,Pd基催化剂抗烧结性能较好且在低温下有优异的反应活性,但贵金属对CO_(2)的吸附较弱,CO_(2)在低温下很难被活化。双金属氧化物催化剂(以ln_(2)O_(3)基和ZrO_(2)基催化剂为主)具有优异的催化性能和良好的稳定性,其中单独的In2O3自身稳定性较差,且In_(2)O_(3)基催化剂的活性相In_(2)O_(3)-x容易被过度还原形成金属In而失活,需要掺杂其他改性元素进一步提高其稳定性和活性;单独的ZrO_(2)催化性能不理想,需要通过与其他金属或金属氧化物相互作用提升其催化性能。稀土元素(La、Ce和Y)作为改性元素或其氧化物作为催化剂载体,能有效调节催化剂的表面酸碱性、活性相分散度和比表面积以及金属-载体相互作用等,从而改善催化剂对CO_(2)的吸附和活化性能,增大产物选择性,并提高催化剂稳定性。综述了La、Ce和Y对Cu基、Pd基和双金属氧化物催化剂的改性作用,以期为稀土元素改性CO_(2)加氢制甲醇催化剂的研发和应用提供参考。

Fossil fuels have an important contribution to human society,but the large amount of CO_(2) emissions has a negative impact on the global climate.CO_(2) hydrogenation to methanol not only effectively reduces the concentration of CO_(2) in the atmosphere,but also provides high value-added chemicals.A range of non-precious metal(Cu)-based,precious metal(Pd)-based and bimetallic oxide catalysts have been used for CO_(2) hydrogenation to methanol.However,conventional Cu-based catalysts suffer from harsh reaction conditions and easy sintering as well as agglomeration of active sites.Pd-based catalysts are more resistant to sintering and have excellent reactivity at low temperatures,but noble metals have weak adsorption of CO_(2),and CO_(2) is difficult to be activated at low temperatures.Bimetallic oxide catalysts(mainly ln_(2)O_(3)-based and ZrO_(2)-based catalysts)have excellent catalytic performance and good stability.Among which,the stability of In_(2)O_(3) alone is poor,and the active phase In_(2)O_(3)-x of In_(2)O_(3)-based catalyst is easily deactivated by excessive reduction to form metal In,which needs to be doped with other modified elements to further improve its stability and activity.The catalytic performance of ZrO_(2) alone for CO_(2) hydrogenation to methanol is not ideal,and its catalytic performance needs to be improved by interacting with other metals or metal oxides.Rare earth elements(La,Ce and Y)as modified elements or their oxides as catalyst carriers can effectively regulate the surface acidity and alkalinity of catalysts,the dispersion of active phases and their specific surface area and metal-carrier interactions,etc.,so as to improve the adsorption and activation capacity of catalysts for CO_(2),increase the selectivity of products and enhance the stability of the catalysts.The modification effects of La,Ce and Y on Cu-based,Pd-based and bimetallic oxide catalysts were reviewed,in order to provide reference for the development and application of catalysts modified by rare earth elements for CO_(2) hydrogenation to methanol.