碱种类及含量对Cu/ZnO/Al_(2)O_(3)催化剂结构及性能的影响

Effect of Alkali Type and Content on Structure and Properties of Cu/ZnO/Al_(2)O_(3) Catalysts

采用共沉淀法制备Cu/ZnO/Al_(2)O_(3)催化剂,考察以Na_(2)CO_(3)、NaHCO_(3)、NaOH和KOH为沉淀剂对催化剂结构及性能的影响,并采用XRD和固定床反应器对催化剂结构及性能进行表征。结果发现,催化剂前驱体受沉淀剂种类、反应液pH值、碱量的影响较大,产物的产量、失重率及结构具有明显的变化。随着一元碱强度的增加,反应产物低温发生分解生成CuO,催化剂产量及焙烧失重率受低温分解的影响较大,但催化剂结晶度提高,性能没有明显的变化,CO_(2)转化率在17%~18%之间,甲醇选择性为35%;而采用二元碱Na_(2)CO_(3),随着碱量的增加,焙烧失重率先减小后增大,催化剂性能明显低于一元碱制备的催化剂,CO_(2)转化率和甲醇选择性分别降至7.5%和13%。提高一元碱的含量,催化剂前驱体中的两性化合物将部分溶解,虽然催化剂活性变化不大,但甲醇选择性从35%降至31%。

Cu/ZnO/Al_(2)O_(3) catalysts were prepared by the co-precipitation method.The effects of Na_(2)CO_(3),NaHCO_(3),NaOH,and KOH as precipitators on the structure and performance of the catalysts were investigated.The structure and performance of the catalysts characterized XRD and fixed-bed reactor.The results showed that the catalyst precursor was greatly affected by the precipitator type,the reaction solution s pH value,and alkali content.The product s yield,weight loss rate,and structure had obvious changes with the increase of mono-base strength,and the reaction product decomposed into CuO at low temperatures.The low-temperature decomposition greatly affected the yield and weight loss rate of the catalyst.Still,the crystallinity of the catalyst increased,and the performance of the catalyst did not change significantly.CO_(2) conversion rate was between 17%~18%,and the methanol selectivity was 35%.However,with the increased alkali content,the weight loss of the binary base Na_(2)CO_(3) decreased first and then increased.The catalyst performance was significantly lower than that of the catalyst prepared by mono-base.The CO_(2) conversion rate and methanol selectivity decreased to 7.5%and 13%,respectively.The amphoteric compounds in the catalyst precursor were partially dissolved by increasing the content of monobasic,and the selectivity of methanol decreased from 35%to 31%.However,the activity of the catalyst remained mostly the same.