摘要
采用四丙基氢氧化铵(TPAOH)处理HZSM-5分子筛,并负载金属Mo.利用XRD、低温氮气吸附、27Al MAS NMR、29Si MAS NMR和NH3-TPD等表征技术对TPAOH改性前后催化剂的结构和酸性进行了研究,考察了其对甲烷甲醇共芳构化反应的催化性能.结构表征结果表明,适量的TPAOH改性可提高HZSM-5分子筛的相对结晶度,样品中介孔含量明显增加并且弱酸量和强酸量也有所增加.反应性能测试表明,以6%Mo负载的HZSM-5(6Mo/HZSM-5)为催化剂,在700℃、甲烷体积空速为2000 h-1的反应条件下,甲烷中添加少量甲醇(nCH4/nCH3OH=20)时,甲烷转化率稳定在10%左右,苯选择性在70%以上,C7-C9高碳芳烃的选择性为4%.在0.1mol/L TPAOH改性6Mo/HZSM-5催化剂上,甲烷转化率为8%左右,苯选择性稳定在60%以上,C7-C9高碳芳烃的选择性提升到10%~17%.利用TG和TPO技术对反应后样品的积碳情况进行了表征,发现甲烷甲醇共进料时催化剂积碳量由甲烷单独进料时的15%降低至5%,0.1mol/L的TPAOH改性后积碳量则进一步降低至1.4%.TPAOH改性的催化剂上介孔含量的增加和强酸中心上的稠环芳烃含量的减少是反应后积碳量显著下降的主要原因,这有利于提高芳构化催化剂的稳定性和碳原子的有效利用率.
A series of HZSM-5 zeolites firstly were treated with different concentrations of tetrapropylammonium hydroxide(TPAOH),and then modified with Mo by incipient impregnation method.Their structures and acidity were systematically characterized by means of XRD,N2 adsorption,27Al MAS NMR,29Si MAS NMR and NH3-TPD.Their catalytic performances in methane and methanol non-oxidative co-aromatization reaction were evaluated.The structural characterization results show that the relative crystallinity of HZSM-5 increases after treating by a proper amount of TPAOH.Moreover,mesopores,weak and strong acid sites also increase obviously in the samples.At 700℃and methane volume space velocity(GHSV)of 2000 h-1,HZSM-5 modified with 6%Mo shows methane conversion of around 10%,benzene selectivity exceeding 70%and C7-C9 high-carbon aromatics selectivity of 4%in the presence of small amount of methanol(nCH4/nCH3OH=20).After modification by 0.1 mol/L TPAOH,the methane conversion decreases to 8%,the benzene selectivity exceeds 60%and the selectivity of C7-C9 high-carbon aromatics increases to 10%~17%.TG and TPO experiments were used to characterize the coke deposition of the samples after reaction.Methane and methanol co-feeding decrease the coke content from 15%of methane feed alone to 5%,and it further decreases to 1.4%after modification by 0.1 mol/L TPAOH.This may be due to the mesopores introduced by the TPAOH treatment and reduced polycyclic aromatics on the strong acid sites,thereby improving the stability of the catalyst and the utilization efficiency of carbon atoms.
作者
王馨瑶
徐禄禄
张维萍
WANG Xin-yao;XU Lu-lu;ZHANG Wei-ping(State Key Laboratory of Fine Chemicals,School of Chemical Engineering,Dalian University of Technology,Dalian 116024,Liaoning,China)
出处
《分子催化》
EI
CAS
CSCD
北大核心
2020年第5期425-435,共11页
Journal of Molecular Catalysis(China)
基金
国家自然科学基金(21673027)。
