Zn物种对CO_(2)氧化乙烷脱氢制乙烯反应的影响研究

Effect of Zn species on oxidative dehydrogenation of ethane to ethylene with CO_(2)

CO_(2)氧化乙烷脱氢制乙烯是一种具有前景的乙烯生产方式,可以使国家在满足内需的情况下增大国际乙烯市场的竞争力.Zn基催化剂在低碳烷烃脱氢制烯烃上具有很高的催化活性,但其应用的关键在于遏制高温反应时Zn元素的流失和提高乙烯选择性.本研究以ZrO_(2)为载体负载Zn,通过XRD、Raman、TEM、UV-vis、XPS、H2-TPR等表征手段结合性能评价说明了由共沉淀法制备的1%ZnZrO_(x)(C)催化剂,可以将Zn元素锚定到ZrO_(2)上,与ZrO_(2)相比,锚定到ZrO_(2)中的Zn元素减少了副反应的发生,提高乙烯选择性的同时,还可以维持催化剂的催化活性.相对于1%ZnZrO_(x)(C)催化剂,由ZnO_(x)和ZrO_(2)直接物理混合而成的1%ZnZrO_(x)(P)催化剂催化活性的提升来自于大量存在于ZrO_(2)表面的聚集态ZnO_(x)物种.相对于锚定到ZrO_(2)上的Zn物种,大量存在于ZrO_(2)表面的ZnO_(x)物种虽然具有极高的活性,但它也导致了严重的乙烷氢解、干重整、积碳和逆水煤气等副反应,并且副反应随反应温度的升高而加剧.因此,在CO_(2)氧化乙烷脱氢制乙烯反应中应尽量避免位于ZrO_(2)载体表面形成聚集态的ZnO_(x)物种.

Oxidative dehydrogenation of ethane to ethylene with CO_(2) is a promising ethylene production method that can increase the competitiveness of a country in the international ethylene market while meeting the domestic demand.Zn based catalysts have high catalytic activity in the dehydrogenation of low-carbon alkanes to olefins,but the key to their application lies in controlling the loss of Zn element during high-temperature reactions and improving ethylene selectivity.This study used ZrO_(2) as a support to load Zn.Characterization methods such as XRD,Raman,TEM,UV-vis,XPS and H_(2)-TPR,combined with performance evaluation were used to demonstrate that the 1% ZnZrO_(x)(C) catalyst prepared by co-precipitation method can anchor the Zn elements onto ZrO_(2).Compared with ZrO_(2),the anchored of Zn elements not only restrain side reactions and improve ethylene selectivity,but also improve the catalytic stability of the catalyst.Compared to the 1% ZnZrO_(x)(C) catalyst,the improvement in catalytic activity of the 1% ZnZrO_(x)(P) catalyst formed by direct physical mixing of ZnO_(x) and ZrO_(2) comes from a large number of aggregated ZnO_(x) species present on the surface of ZrO_(2).Compared to the anchored Zn species on ZrO_2,although the abundant ZnO_(x) species on ZrO_(2) have well activity,but they also lead to serious side reactions such as ethane hydrocraking,dry reforming,carbon deposition,and reverse water gas reaction,which intensify with the increase of reaction temperature.Therefore,it is suggested to avoid the formation of aggregated ZnO_(x) species on the surface of the ZrO_(2) support as much as possible in the CO_(2) oxidation of ethane dehydrogenation to ethylene reaction.