焙烧温度对CoAl-LDH基催化剂结构和费托合成性能的影响

Influence of calcination on structure of CoAl-LDH based catalyst and its catalytic performance in Fischer-Tropsch synthesis

采用尿素水解法制备了层状双金属氢氧化物(CoAl-LDHs),经焙烧处理后得到LDH基催化剂,利用XRD、BET、SEM等分析方法对其进行表征,并在固定床上考察了焙烧温度对催化剂的层状结构及费托合成反应性能的影响。结果表明,热解LDHs会生成层状双分子氧化物(LDO),热解温度对催化剂的晶型结构、颗粒分散度和还原性能有显著影响;催化剂中钴的负载量可达50.0%以上,钴氧化物颗粒均匀分散在纳米片上,同时具有较大的比表面积。其中600℃焙烧LDHs形成催化剂的催化活性最佳,在反应温度220℃、V(H_(2))∶V(CO)=2∶1、反应压力2.5 MPa和空速为3.8 h^(-1)的条件下,CO转化率为22%,C_(5+)选择性可达91.4%。

CoAl-LDHs,a kind of layered double hydroxides(LDH)is prepared via urea hydrolysis method,and calcined at different temperature to form LDH-based catalyst for Fischer-Tropsch synthesis.The catalyst samples are characterized by means of XRD,BET and SEM etc.,and the influences of calcination temperature on their structure and catalytic performance for Fischer-Tropsch synthesis are evaluated in a fixed-bed micro-reactor.It is indicated that the calcination of LDHs can lead to the formation of layered double oxides(LDOs),and calcination temperature has significant impact on the crystallinity,particle dispersion and reducibility of the catalyst.The catalyst prepared in this way can have a high cobalt loading amount of over 50%and a larger specific surface area,in which cobalt oxides particles disperse evenly on the surface of LDOs nanosheets.Among all the samples,the catalyst sample calcined at 600℃yields the best activity,over which CO conversion reaches 22%and C5+selectivity reaches 91.4%at 220℃,2.5 MPa,a H_(2):CO volumetric ratio of 2:1 and a velocity of 3.8 h^(-1).