Dauda Ibrahim B, Yusuf Mustapha, Gbadamasi Sharafadeen, Bello Mukhtar, Atta Abdulazeez Y, Aderemi Benjamin O, Jibril Baba Y
Department of Chemical Engineering, Ahmadu Bello University, Zaria 810261, Nigeria.
National Research Institute for Chemical Technology, P.M.B 1052, Basawa, Zaria 810222, Nigeria.
ACS Omega. 2020 Feb 10;5(6):2725-2733. doi: 10.1021/acsomega.9b03343. eCollection 2020 Feb 18.
Hierarchical ZnO/ZSM-5 catalysts were prepared by desilication and impregnation with 2 wt % metallic ZnO. X-ray diffraction and Fourier transform infrared (FTIR) results showed that the structures of the hierarchical zeolites were relatively preserved despite desilication but were accompanied with sequential loss in crystallinity, likewise Bro̷nsted acidity causing decline in conversion or activity of the catalyst. However, pyridine FTIR shows enhancement of the Bro̷nsted acidic sites. Throughout the activity test, the hierarchical ZnO/ZSM-5 catalysts showed an outstanding performance within 5 h on stream with the average aromatic (benzene, toluene, and xylenes) selectivity trend, represented by their NaOH concentrations 0.3 M > 0.4 M > 0.2 M > 0.1 M corresponding to 61.0, 53.5, 40.3, and 36.8%, respectively. Their average propane conversions within the same period followed a consecutive trend 0.1 M > 0.2 M > 0.3 M > 0.4 M conforming to 34.1, 24.8, 17.3, and 10.2%, respectively. These were compared with that of the reference (ZnO/ZSM-5), which exhibited an average aromatic selectivity of 25.2% and propane conversion of 39.7%. Furthermore, the hierarchical catalyst generally displayed a low amount of C9+ heavier aromatics with the ZnO/ZSM-5(0.3 M) catalyst having the lowest C9+ selectivity of 23.7% compared to the reference catalyst with 72.7% at the same time on stream.
通过脱硅和用2 wt%的金属氧化锌浸渍制备了分级结构的ZnO/ZSM-5催化剂。X射线衍射和傅里叶变换红外光谱（FTIR）结果表明，尽管进行了脱硅处理，但分级沸石的结构相对保持完整，但结晶度随之逐渐降低，同样，布朗斯台德酸度导致催化剂的转化率或活性下降。然而，吡啶FTIR显示布朗斯台德酸性位点有所增强。在整个活性测试过程中，分级结构的ZnO/ZSM-5催化剂在5小时的运行时间内表现出优异的性能，其平均芳烃（苯、甲苯和二甲苯）选择性趋势由它们的氢氧化钠浓度表示，0.3 M > 0.4 M > 0.2 M > 0.1 M，相应的选择性分别为61.0%、53.5%、40.3%和36.8%。在同一时期内，它们的平均丙烷转化率呈现连续趋势，0.1 M > 0.2 M > 0.3 M > 0.4 M，分别对应34.1%、24.8%、17.3%和10.2%。将这些结果与参比样品（ZnO/ZSM-5）进行比较，参比样品的平均芳烃选择性为25.2%，丙烷转化率为39.7%。此外，分级催化剂通常显示出较低含量的C9+重芳烃，其中ZnO/ZSM-5(0.3 M)催化剂的C9+选择性最低，为23.7%，而参比催化剂在相同运行时间的C9+选择性为72.7%。
