ZnCrO_x/HZSM-5催化合成气直接转化制异构烷烃

Direct synthesis of isoalkanes from syngas over ZnCrO_x/HZSM-5 catalyst

分别采用共沉淀法和水热法制备了ZnCrO_x复合金属氧化物和HZSM-5沸石,通过物理混合得到双功能催化剂,实现了合成气一步高选择性制备异构烷烃。采用XRD、TEM、氮吸附和NH3-TPD等技术对催化剂进行了表征,考察了双功能催化剂中HZSM-5沸石组分硅铝比以及ZnCrO_x/HZSM-5质量比(OX/ZEO mass ratio)对合成气催化转化反应性能的影响。结果表明,随着HZSM-5硅铝比的增加,催化剂酸密度下降,CO转化率略有下降,产物中C5+选择性显著提高,异构烷烃比例不断增加。此外,在保证CO转化率的前提下提高双功能催化剂中ZnCrO_x组分的比例,产物中C5+的选择性也显著上升。在400℃、2.0 M Pa、进料空速(GHSV)为3600 mL/(h·gcat)的条件下,合成气(H2/CO(volume ratio)=2)转化率达到35%,C5+选择性超过44%,且C5+中异戊烷比例高达65%。

ZnCrO x composite oxide and HZSM-5 zeolite were prepared by using the coprecipitation and hydrothermal methods,respectively;after that,a bi-functional ZnCrO x/HZSM-5 catalyst was obtained through physical mixing of ZnCrO x with HZSM-5 and used in the direct synthesis of isoalkanes from syngas.The ZnCrO x/HZSM-5 catalyst was characterized by XRD,TEM,N 2 sorption,and NH 3-TPD and the effects of Si/Al ratio in HZSM-5 and the mass ratio of ZnCrO x to HZSM-5(OX/ZEO mass ratio)on the catalytic performance of ZnCrO x/HZSM-5 in syngas conversion were investigated.The results indicated that with the increase of Si/Al ratio in HZSM-5,the catalyst acid density is decreased,resulting in a lower CO conversion but higher selectivity to C 5+products and higher isoparaffin fraction.Moreover,the selectivity to C 5+products is significantly increased by increasing the proportion of ZnCrO x components in the bifunctional catalyst without losing CO conversion.For the syngas conversion over ZnCrO x/HZSM-5 catalyst under the conditions of 400℃,2.0 MPa,gas hourly space velocity(GHSV)of 3600 mL/(h·g cat),the conversion of syngas reaches 35%,with a selectivity of 44%to C 5+products and an isopentane fraction up to 65%in the C 5+products.