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CO_2引起的气候变化已引起全世界的关注,但同时CO_2也是一种可持续的碳资源.将CO_2转化为高附加值的燃料或化学品不仅可以解决CO_2的问题,还可变废为宝得到有用的化学品.CO_2加氢制甲醇是实现这一过程的理想选择之一,因为甲醇不仅是很好的燃料,还可转化得到烯烃、芳烃等高附加值化学品,需要强调的是整个过程所需的氢气是利用太阳能等可再生能源通过光催化、光电催化或电解水制氢得到.使用煤或天然气经合成气用CuZnOAl_2O_3催化剂合成甲醇已工业化50年左右,甲醇选择性可达99%,但该催化剂应用于CO_2加氢制甲醇时,较强的逆水煤气变换副反应致使甲醇选择性只有60%左右,另外,反应生成的水会加速Cu基催化剂的失活.因此,开发新型高选择性催化体系显得尤为必要,世界上很多科学家展开了新型催化剂的研发,如Cu/ZnO/ZrO_2,Pd/ZnO,“georgeite”Cu,Cu(Au)/CeO_x/TiO_2,Ni-Ga,MnO_x/Co_3O_4催化剂等,但这几类催化剂体系上甲醇选择性都不超过60%,CO_2加氢制甲醇选择性低的问题一直没有解决.近期,中国科学院大连化学物理研究所李灿院士课题组开发了一种不同于传统金属催化剂的双金属固溶体氧化物催化剂ZnO-ZrCO_2,在近似工业条件下(5.0 MPa,24000 mL/(g h),H_2/CO_2=3/1~4/1,320~315 ℃),当CO_2单程转化率超过10%时,甲醇选择性仍保持在90%左右,是目前同类研究中综合水平最好的结果.研究表明,该催化剂的固溶体结构特征提供了双活性中心反应位点,Zn和Zr,其中H_2和CO_2分别在Zn位和原子相邻的Zr位上活化,在CO_2加氢过程中表现出了协同作用,从而可高选择性地生成甲醇.原位红外-质谱同位素实验及DFT理论计算结果表明,表面HCOO*和H_3CO*是反应主要的活性中间物种.该催化剂反应连续运行500 h无失活现象,还具有极好的耐烧结稳定性和一定的抗硫能力,表现出了良好的工业应用前景.传统甲醇合成Cu基催化剂要求原料气含硫低于0.5 ppm,而该催化剂的抗硫能力无疑可使原料气净化成本大大降低,在工业应用方面表现出潜在的优势.
The climate change caused by CO_2 has aroused the world’s attention, but at the same time CO_2 is also a sustainable carbon resource.Carbon dioxide into high value-added fuels or chemicals can not only solve the problem of CO_2, but also turn waste into treasure Useful chemicals .CO_2 Hydrotreating methanol is one of the ideal choices for this process because methanol is not only a good fuel, but it can also be converted to high value-added chemicals such as olefins and aromatics. What needs to be emphasized is that the entire process The required hydrogen is obtained by photocatalysis, photoelectrocatalysis or electrolysis of hydrogen from renewable sources such as solar energy, etc. The synthesis of methanol from CuZnOAl 2 O 3 catalyst using coal or natural gas via synthesis gas has been industrially produced for about 50 years with methanol selectivity up to 99% However, when the catalyst is applied to the hydrogenation of methanol to methanol, the selectivity of methanol is only about 60% due to the strong side-by-side reaction with reverse water gas conversion. In addition, the water generated by the reaction accelerates the deactivation of the Cu-based catalyst. The catalytic system is particularly necessary. Many scientists in the world have developed new catalysts such as Cu / ZnO / ZrO 2, Pd / ZnO, “georgeite” Cu, Cu (Au) / CeO x / TiO 2, Ni-Ga, However, these types of catalyst system methanol selectivity of not more than 60%, CO_2 hydrogenation of methanol to the low selectivity of the problem has not been solved recently, Institute of Chemical Physics, Chinese Academy of Sciences Li Chan academician A bimetallic solid solution oxide catalyst, ZnO-ZrCO 2, which is different from the traditional metal catalysts, has been developed under the conditions of approximate industrial conditions (5.0 MPa, 24000 mL / (gh), H 2 / CO 2 = 3/1 ~ 4/1,320 ~ 315 ℃ ), The selectivity of methanol remains at about 90% when the single pass conversion rate of CO_2 is over 10%, which is the best comprehensive result in the same kind of studies at present.It has been shown that the structural characteristics of the solid solution of the catalyst provide double active center reaction sites Point, Zn and Zr, in which H 2 and CO 2 were activated respectively at the Zn site and the Zr site adjacent to the atom, and synergistic effect was observed during the hydrogenation of CO 2, thus the methanol could be selectively synthesized. In situ FTIR Isotope experiments and DFT theoretical calculations show that the surface HCOO * and H_3CO * are the main reactive intermediate species, and the catalyst has no deactivation after 500 hours continuous operation, excellent sintering stability and sulfur resistance , Showed good Good prospects for industrial applications.Traditional methanol synthesis of Cu-based catalyst requires feed gas sulfur content of less than 0.5 ppm, and the catalyst’s sulfur resistance will undoubtedly make the feed gas purification costs greatly reduced, showing potential advantages in industrial applications.