Wei Wu

Synthesis of microscale and nanoscale ZSM-5 zeolites: effect of particle size and acidity of Zn modified ZSM-5 zeolites on aromatization performance

Microscale and nanoscale HZSM-5 zeolites, MZ5 and NZ5, have been successfully synthesized by using a template-free and an in situ seed-induced method, respectively; the synthesized zeolites were then modified by Zn impregnation to obtain Zn-modified catalysts, Zn/MZ5 and Zn/NZ5. Various techniques, including XRD, SEM, 27Al MAS NMR, N2 adsorption, H2-TPR, XPS, NH3-TPD, Py-IR and TG/DTA, were used in the characterization of the catalysts, and their catalytic performance in the aromatization of 1-hexene was investigated to correlate the particle size, acidity and catalytic behavior. Compared to MZ5, the NZ5 sample exhibited better catalytic stability due to its smaller particle size and weaker acid strength. Both Zn-modified catalysts showed increased BTX yield because of the smaller B/L ratio and newly formed stronger Lewis acid sites provided by the [ZnOZn]2+ species, which effectively facilitated the dehydrogenation process in the aromatization. The highest BTX yield of 57.93 wt% was obtained for the Zn/NZ5 sample.

Hydroisomerization of n-hexadecane over a Pd–Ni2P/SAPO-31 bifunctional catalyst: synergistic effects of bimetallic active sites

A series of bifunctional catalysts are prepared by loading Pd, Ni2P and bimetallic Pd–Ni2P on di-n-butylamine(DBA)-templated SAPO-31 molecular sieves through either impregnation or impregnation combined with temperature-programmed reduction methods. All bifunctional catalysts are characterized using XRD, N2 adsorption, 27Al and 31P MAS NMR, SEM, TEM, IR spectroscopy of adsorbed pyridine, XPS, H2 chemisorption, ICP, and TG–DTG measurements. The catalytic performance over all prepared bifunctional catalysts is compared for n-hexadecane hydroisomerization. The obtained results demonstrate that the 0.05Pd–4Ni2P/S31 catalyst produces a higher iso-C16 yield of 72.7% with n-C16 conversion of 83.1% compared with the other two catalysts. This result is attributed to two reasons: i) the bimetallic Pd–Ni2P component possesses stronger (de)hydrogenation functionality than Ni2P does, and ii) the bimetallic bifunctional catalyst has a better balance between metal and acid functionality than the monometallic catalysts do. Moreover, the 0.05Pd–4Ni2P/S31 catalyst also shows the best catalytic stability among all catalysts, since the n-C16 conversion and iso-C16 selectivity are still above 80% and 90%, respectively, even after 100 h of long-term testing. Therefore, the present study has provided a novel idea for the design of bimetallic bifunctional catalysts for long-chain n-alkane hydroisomerization.