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首页> 外文期刊>Catalysis science & technology >CO2 hydrogenation to methanol and hydrocarbons over bifunctional Zn-doped ZrO2/zeolite catalysts
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CO2 hydrogenation to methanol and hydrocarbons over bifunctional Zn-doped ZrO2/zeolite catalysts

机译：二氧化碳加氢甲醇和碳氢化合物通过双官能Zn-doped氧化锆/沸石催化剂

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摘要

The tandem process of carbon dioxide hydrogenation to methanol and its conversion to hydrocarbons over mixed metal/metal oxide-zeotype catalysts is a promising path to CO2 valorization. Herein, we report three Zn-doped ZrO2 catalysts prepared by co-precipitation of Zn- and Zr-containing salts to obtain three different loadings of Zn (5, 15 and 30 wt%). In the context of bifunctional catalysts, we combined ZrZnOX with two of the most performing zeolite/zeotype catalysts for the methanol-to-hydrocarbons (MTH) reaction: H-ZSM-5 and H-SAPO-34. Catalytic testing at 250-350 degrees C and 20-40 bar revealed that H-ZSM-5 is more stable and more capable of converting methanol at low temperature, whereas H-SAPO-34 shows the highest C3 selectivity. The best performance was observed for the ZrZnOX sample with 30% Zn, combined with ZSM-5 at 350 degrees C, 30 bar and H-2/CO2/N-2 = 6/2/1. Under these conditions, the equilibrium methanol yield was observed after 0.4 s g(-1) ml(-1) over ZrZnOX alone. Mixing with ZSM-5 in a 1 : 1 weight ratio, methanol was rapidly converted to hydrocarbons, with an optimum C-3 productivity of 1.5 mol kg-1 h(-1) at 24000 ml h(-1) g(-1). An extensive surficial, textural and structural characterization of ZrZnOX alone was carried out by FT-IR spectroscopy, N-2 adsorption/desorption at liquid nitrogen temperature, PXRD and XAS. Formation of a ZrZnOX tetragonal solid solution was confirmed for all the samples (PXRD, XAS). The amount of Zr4+ sites at the surface was found to decrease, while the number of oxygen vacancies increased after H-2 treatment at 400 degrees C, coherent with an increase of Zn loading (FT-IR). DFT modelling pointed out that once a stoichiometric oxygen vacancy is induced by the presence of Zn, the formation of extra oxygen vacancies during activation is thermodynamically favored. Moreover, i) the oxygen vacancies were found to play an active role in CO2 hydrogenation, in accordance with experimental data, and ii) methanol is most likely formed via the formate pathway, and is energetically favored compared to CO formation, in agreement with the high methanol selectivity observed experimentally at low CO2 conversion. Importantly, operando-XAS, XPS, TEM and PXRD studies of the as-prepared, pretreated and tested catalysts showed that the structure and composition of the catalyst is not affected by the reaction. Indeed, a final catalytic test carried out on the regenerated ZrZnOX/H-ZSM-5 catalyst showed that the initial performances were completely restored and no Zn exchange in the zeolite was observed neither before nor after testing.
机译：的串联过程二氧化碳加氢甲醇及其转化为碳氢化合物在混合金属/金属oxide-zeotype催化剂一个有前途的道路二氧化碳稳定物价。报告三个Zn-doped锆催化剂由共同沉淀锌和Zr-containing盐获得三种不同载荷的锌(5、15和30 wt %)。催化剂,我们结合ZrZnOX和两个的大多数执行沸石/ zeotype催化剂methanol-to-hydrocarbons (m)反应:H-ZSM-5和H-SAPO-34。度和20 - 40条显示H-ZSM-5更稳定、更有能力的转换低温甲醇,而H-SAPO-34显示了C3选择性最高。ZrZnOX样本的性能观察有30%的锌、结合ZSM-5在350度30酒吧和h2 / CO2 / C, n = 6/2/1。甲醇产量条件下,平衡观察后0.4 s g(1)在ZrZnOX毫升(1)一个人。甲醇迅速转化为碳氢化合物,的最优供给效率1.5摩尔公斤h在24000毫升(1)h g(1)(1)。地表结构和结构表征ZrZnOX单独进行通过红外光谱,n -吸附/解吸在液氮温度下,PXRD和xa。组建一个ZrZnOX正方固溶体确认所有样品(PXRD xa)。Zr4 +网站的数量在表面被发现空缺职位的数量减少,而氧气增加2治疗后在400摄氏度,连贯的增加锌加载(红外光谱)。DFT模型指出,一次化学氧空位诱导的锌,形成额外的氧气在激活就是热动力空缺青睐。发现在二氧化碳发挥积极作用加氢,依照实验数据和ii)甲醇最有可能通过形成的甲酸通路,并大力支持公司形成相比,在协议高甲醇选择性观察实验在低二氧化碳转换。XPS、TEM和PXRD研究好了,进行预处理和测试表明,该催化剂催化剂的结构和组成反应的影响。催化测试进行再生ZrZnOX / H-ZSM-5表明最初的催化剂表演完全恢复和锌观察交换的沸石之前和之后的测试。

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