Study on different synthesis methods of ZnxCe2-yZryO4/SAPO-34 catalyst and its catalytic performance in syngas to low-carbon olefins
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摘要: 通过溶胶凝胶法、水热法、共沉淀法合成了不同的ZnxCe2-yZryO4金属氧化物，并对其结构性质进行了XRD、BET、HRTEM、CO-TPD、Raman以及XPS等多种技术表征。考察不同合成方法（溶胶-凝胶法、共沉淀法和水热法）所制备的ZnxCe2-yZryO4金属氧化物形貌、晶粒粒径和氧空穴浓度变化情况，及其对合成气制低碳烯烃性能的影响。结果表明，ZnxCe2-yZryO4固溶体的形貌、暴露晶面、晶粒粒径和表面氧空穴浓度强烈依赖于合成方法。在300 ℃、1.0 MPa条件下，采用溶胶-凝胶法制备的ZnxCe2-yZryO4与SAPO-34组成的双功能催化剂具有最高的低碳烯烃（C2-4=）选择性（79.5%），同时甲烷和CO2的选择性分别仅为5.5%和10.7%。实现了低温低压条件直接转化合成气制低碳烯烃，同时大幅降低了甲烷和CO2的释放。Abstract: A series of ZnxCe2-yZryO4 metal oxides were synthesized by sol gel method, hydrothermal method and co-precipitation method respectively and characterized by XRD, BET, HRTEM, CO-TPD, Raman and XPS. The effects of the synthesis method on the morphology, grain size and oxygen vacancy concentration and the catalytic performance in syngas to low-carbon olefin reaction of the ZnxCe2-yZryO4 catalysts were investigated. The results show that the shape, exposed crystal surface, grain size and surface oxygen vacancy concentration of ZnxCe2-yZryO4 solid solution are strongly dependent on the synthesis method. Under the reaction conditions of 300 ℃ and 1.0 MPa, the dual-functional catalysts of ZnxCe2-yZryO4/SAPO-34 prepared by sol-gel method have the highest low-carbon olefin (C2-4=) selectivity (79.5%), while the selectivities of methane and CO2 are only 5.5% and 10.7%, respectively. Here the direct conversion of syngas to low-carbon olefins are realized at low temperature and pressure and the formation of methane and CO2 is greatly reduced.
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图 1 不同合成方法制备的ZnxCe2-yZryO4固溶体的XRD谱图
Figure 1 XRD patterns of the ZnxCe2-yZryO4 solid solutions prepared with different methods
图 2 不同合成方法制备ZnxCe2-yZryO4的TEM照片和粒径分布
(a): sol-gel method; (b): hydrothermal method; (c): co-precipitation method
Figure 2 TEM images and size distributions (estimated by counting 100 NPs) of the ZnxCe2-yZryO4 solid solutions prepared with different methods
图 3 不同合成方法制备的ZnxCe2-yZryO4固溶体氮气吸附-脱附曲线以及相应的孔径分布
Figure 3 N2 absorption-desorption isotherms (a) and corresponding pore size distribution (b) of the ZnxCe2-yZryO4 solid solutions prepared with different methods
图 4 不同合成方法制备的ZnxCe2-yZryO4/ SAPO-34双功能催化剂上CO转化率与产物分布
Figure 4 CO conversion and product distribution over the ZnxCe2-yZryO4/SAPO-34 dual functional catalyst
图 5 不同合成方法制备的ZnxCe2-yZryO4拉曼光谱谱图
Figure 5 Raman spectra of the ZnxCe2-yZryO4 catalyst prepared with different methods
图 6 不同合成方法制备ZnxCe2-yZryO4固溶体的O 1s XPS谱图(a)以及Ce 3d XPS谱图(b)
Figure 6 O 1s XPS spectra (a) and Ce 3d XPS spectra (b) of the ZnxCe2-yZryO4 solid solutions prepared with different methods
图 7 不同合成方法制备ZnxCe2-yZryO4固溶体的CO-TPD谱图
Figure 7 CO-TPD profiles of the ZnxCe2-yZryO4 solid solutions prepared with different methods
表 1 不同合成方法制备的ZnxCe2-yZryO4/SAPO-34合成气制烯烃反应产物分布和CO转化率
Table 1 CO conversion and product distribution of the ZnxCe2-yZryO4/SAPO-34 dual functional catalysts
Sample Selectivitys/% CO conversion x/% CO2 selectivity s/% C2-4= C2-40 CH4 others ZnCeZr(s)a /SAPO-34 79.5 4.1 5.5 10.9 6.4 10.7 ZnCeZr(h)b /SAPO-34 77.0 3.0 6.4 13.5 5.4 4.5 ZnCeZr(c)c/SAPO-34 73.1 9.4 6.7 10.8 6.6 12.6 a: sol-gel method; b: hydrothermal method; c: co-precipitation method 
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表 2 不同合成方法制备的ZnxCe2-yZryO4表面氧空穴浓度
Table 2 Concentration of surface oxygen vacancies of the ZnxCe2-yZryO4 catalyst prepared with different methods
Sample Ov/Ototal (%)a Odefect(%)b Ce3+/(Ce4++Ce3+) (%)c ZnCeZr(sol-gel) 23.8% 29.7% 30.0% ZnCeZr(hydrothermal) 15.9% 25.5% 24.5% ZnCeZr(co-precipitation) 15.7% 27.7% 25.3% a: the Ov/Ototal ratio was obtained from the Raman spectra by the equation: Ov/Ototal=I630/(I475+I630), whereI630 andI475 correspond to the intensity of peaks at 600 and 475cm-1, respectively;
b: the Odefect(Ovacancy) concentration was calculated from the O 1s XPS spectra by the equation: concentration of Odefect=IOdefect/(IOdefect+IOlattice), whereIOdefect andIOlattice correspond to the intensity of peaks at 530.5 and 529.5eV, which are assigned to Ovacancy(Odefect) and lattice oxygen species (Olattice) respectively;
c: the proportion of Ce3+ (P(Ce3+)) on the surface was calculated from the Ce 3d XPS spectra by the equation:$p\left( {{\rm{C}}{{\rm{e}}^{3 + }}} \right) = \frac{{I\left( {{{\rm{u}}_1}} \right) + I\left( {{{\rm{v}}_1}} \right)}}{{\sum\limits_i {\left( {I\left( {{{\rm{u}}_i}} \right) + I\left( {{{\rm{v}}_i}} \right)} \right)} }} $whereI(x) represents the intensity ofu0 (900.9eV) andv0 (882.5eV), u1(903.2eV) andv1 (884.7eV), u2 (907.3eV) andv2 (888.8eV), andu3 (916.6eV) andv3 (898.4eV) signals, respectively, in Ce 3d XPS spectra
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