煅烧温度对ZnGaZrO_(x)/SAPO-34催化性能的影响

Effect of calcination temperature on catalytic performance of ZnGaZrO_(x)/SAPO-34

在CO_(2)加氢制低碳烯烃(C_(2)^(=)-C_(4)^(=))中,双功能催化剂的煅烧温度对其催化性能具有显著影响。基于此,采用共沉淀法制备了ZnGaZrO_(x)氧化物,水热法制备了SAPO-34分子筛,然后对两者进行研磨制得ZnGaZrO_(x)/SAPO-34双功能催化剂,并考察煅烧温度对ZnGaZrO_(x)和SAPO-34物化性质及催化性能的影响。通过XRD、XPS、H_(2)/CO_(2)/NH_(3)-TPD、SEM、N_(2)吸附-脱附和原位DRIFTS表征发现,在制备ZnGaZrO_(x)过程中,当煅烧温度为650℃时,ZnGaZrO_(x)具有最强的H_(2)和CO_(2)吸附活化能力,能有效提高HCOO*和CH_(3)O*的生成速率和浓度,促进甲醇产物生成;在制备SAPO-34过程中,当煅烧温度为450℃时,分子筛比表面积最大、晶粒尺寸最小、强酸位点的酸性最弱,能有效避免低碳烯烃发生二次加氢,从而获得较高的低碳烯烃选择性。最佳条件下合成的ZnGaZrO_(x)/SAPO-34双功能催化剂在反应温度为390℃、压力为3 MPa、空速为3600 mL/(g∙h)条件下,CO_(2)转化率为28.3%,CO选择性仅为44.6%,C_(2)^(=)-C_(4)^(=)选择性为84.4%,C_(2)^(=)-C_(4)^(=)产率高达13.2%,且在反应100 h内催化性能无明显衰减。该工作为双功能催化剂的改性提供了新的研究思路。

In the hydrogenation of CO_(2) to low-carbon olefins(C_(2)^(=)-C_(4)^(=)),the calcination temperature of the bifunctional catalyst has significant effects on its catalytic performance.Based on this,ZnGaZrO_(x) oxides were prepared by coprecipitation method and SAPO-34 molecular sieves were prepared by hydrothermal method,and then both of them were milled to produce ZnGaZrO_(x)/SAPO-34 bifunctional catalysts,and the effects of calcination temperature on the physicochemical properties and catalytic performance of ZnGaZrOx and SAPO-34 were investigated.It was found by XRD,XPS,H_(2)/CO_(2)/NH_(3)-TPD,SEM,N_(2) adsorptiondesorption and in situ DRIFTS characterization that during the preparation of ZnGaZrOx,when the calcination temperature was 650℃,ZnGaZrO_(x) had the strongest activation ability of H_(2) and CO_(2) adsorption,and it could effectively increase the rate and concentration of the generation of HCOO*and CH_(3)O*to promote the methanol product generation.During the preparation of SAPO-34,when the calcination temperature was 450℃,the molecular sieve had the largest specific surface area,the smallest grain size,and the weakest acidity of the strong acid site,which could effectively avoid the secondary hydrogenation of low-carbon olefins,thus obtaining higher selectivity of low-carbon olefins.The ZnGaZrO_(x)/SAPO-34 bifunctional catalysts synthesized under the optimal conditions showed a CO_(2) conversion of 28.3%,a CO selectivity of only 44.6%,a C_(2)^(=)-C_(4)^(=)selectivity of 84.4%,a C_(2)^(=)-C_(4)^(=)yield of as high as 13.2%at a reaction temperature of 390℃,a pressure of 3 MPa,and an airspeed of 3600 mL/(g∙h).And the catalytic performance did not decay significantly within 100 h of reaction.This work provided a new research idea for the modification of bifunctional catalysts.