Effects of Crystallite Sizes of Pt/HZSM-5 Zeolite Catalysts on the Hydrodeoxygenation of Guaiacol

Abstract

Herein, Pt/HZSM-5 zeolite catalysts with different crystallite sizes ranging from nanosheet (~2 nm) to bulk crystals (~1.5 μm) have been prepared for the hydrodeoxygenation of guaiacol, and their effects on the reaction pathway and product selectivity were explored. HZSM-5 zeolites prepared by seeding (Pt/Z-40: ~40 nm) or templating (Pt/NS-2: ~2 nm) fabricated intra-crystalline mesopores and thus enhanced the reaction rate by promoting the diffusion of various molecules, especially the bulky ones such as guaiacol and 2-methoxycyclohexanol, leading to a higher cyclohexane selectivity of up to 80 wt % (both for Pt/Z-40 and Pt/NS-2) compared to 70 wt % for bulky HZSM-5 (Pt/CZ: ~1.5 μm) at 250 °C and 120 min. Furthermore, decreased crystallite sizes more effectively promoted the dispersion of Pt particles than bulky HZSM-5 (Pt/Z-400: ~400 nm and Pt/CZ). The relatively low distance between Pt and acidic sites on the Pt/Z-40 catalyst enhanced the metal/support interaction and induced the reaction between the guaiacol molecules adsorbed on the acidic sites and the metal-activated hydrogen species, which was found more favorable for deoxygenation than for hydrogenation of oxygen-containing molecules. In addition, Pt/NS-2 catalyst with a highly exposed surface facilitated more diverse reaction pathways such as alkyl transfer and isomerization.

Study of the Hydrogen Pretreatment of Gallium and Platinum Promoted ZSM-5 for the Ethane Dehydroaromatization Reaction

“…Duan et al associated the peaks at 71 and 75 eV with Pt 0 and Pt 2+ , respectively. In the reduced GaPt and Pt catalysts, the Pt 4f 5/2 peak could not be resolved, which confirms the reduction of Pt 2+ , which is consistent with the H 2 -TPR results. , …”

“…The second peak indicates a strong interaction between Pt and the surface of the support. 14,41,46 Following the hydrogen reduction of the bulk fresh-Pt, the second H 2 -TPR shows the catalyst was fully reduced.…”

“…In the reduced GaPt and Pt catalysts, the Pt 4f 5/2 peak could not be resolved, which confirms the reduction of Pt 2+ , which is consistent with the H 2 -TPR results. 41,46 3.2. Investigation of Acidity of Fresh and Reduced Catalysts Prior to Ethane DHA Reaction by Pyridine DRIFTS.…”

“…The low-temperature peak corresponds to the reduction of Pt 2+ to Pt 0 and weak interaction with the support. The second peak indicates a strong interaction between Pt and the surface of the support. ,, Following the hydrogen reduction of the bulk fresh-Pt, the second H 2 -TPR shows the catalyst was fully reduced.…”

Synergistic Effect in Vapor Phase Hydrodeoxygenation on USY Zeolite Supported Ir–Pt Catalyst: Role of Pentacoordinated Al3+ Ions

“…36 In this regard, the recent investigation of the effect of the crystal size of Pt/ZSM-5 zeolites on the HDO of guaiacol by Duan et al showed that decreasing the ZSM-5 crystal size enhanced the dispersion of Pt, which favored the reaction between the reactive molecules adsorbed on the acid sites and the atomic hydrogen, the deoxygenation being more promoted than the hydrogenation of the O-containing compound. 30 Similarly, the more active Ir−Pt/USY exhibits a smaller zeolite crystal size than its less active Ir−Pt/ZSM-5 counterpart (Table 1), confirming the better metal dispersion of the former catalyst observed by HRTEM. Interestingly, the HDO activity of the ZSM-supported catalysts decreased linearly with an increase in the zeolite crystal size (see Figure S4 of the Supporting Information) suggesting an enhancement of the metal dispersion going from the Ir/ZSM-5 to the Ir−Pt/ZSM-5 catalyst.…”