Enhanced alkene productivity in methanol-to-hydrocarbons conversion using a second catalyst component and hydrogen co-feeds
Alkenes with three or more carbon atoms (C3+) are essential platform molecules for producing polymers, rubbers, and specialty chemicals, and can also be oligomerized into jet-fuel range hydrocarbons for sustainable aviation fuels (SAFs).[1] Current methanol-to-hydrocarbons (MTH) processes efficiently produce ethene and propene, yet the selective formation of C3+ alkenes remains a significant challenge.[2] Unidimensional (1D) zeolites (e.g., ZSM-22, ZSM-23 and ZSM-48) are especially selective for this hydrocarbon fraction, but suffer from rapid catalyst deactivation due to coke deposition.[3] Herein, we introduce a novel multicomponent catalyst (MCC) concept combining a secondary catalyst component with hydrogenating function (e.g., Pd/SiO2) with the pristine zeolite under ambient pressure H2 co-feeding. This approach extends catalyst lifetime by up to one order of magnitude, while retaining the inherently high yield of C3+ olefins, resulting in a net increase in alkene productivity (Figure 1a). The enhancement is maintained across a wide range of H2 concentrations and Pd/SiO2:zeolite weight ratios, providing flexibility to minimize both Pd and H2 use. Kinetic investigations indicate that this effect stems from the selective interception of deactivating intermediates, such as formaldehyde and dienes, curtailing coke-forming pathways. Consistently, operando DR-UV-vis spectroscopy (Figure 1b) shows that, with H2, Pd/SiO2 leads to reduced accumulation of coke species, particularly higher polycyclic aromatics (h-PAHs), ascribed to external coke. Following an induction period, where the system is more hydrogenative, alkene selectivity rises to that of the parent zeolite. Operando XAS measurements (Figure 1c) indicate that Pd exists as Pd(0) throughout the reaction with no major restructuring, pointing to weaker surface poisoning as the trigger toward milder hydrogenating activity. The drop-in nature of the SCC, together with ambient pressure operation, offers great promise for scalability. Studies are in progress to optimize the Pd speciation within the SCC, and to develop MCC catalysts in technical form.
Figure 1. a Methanol conversion (X) and selectivity toward C3-5 alkenes (SC3-5=) versus methanol cumulative turnover (CT). The cumulative olefin productivity (CPC3-5=) is shown in inset. b DR-UV-vis spectra acquired during the MTH reaction over the MCC, with/without H2 co-feed, with band assignments for the main coke species, and c Pd K-edge XANES spectra of the MCC acquired during MTH operation.
[1] F. J. Dubray, V. Paunović, J. A. van Bokhoven, ACS Sustainable Chemistry & Engineering, 2024, 12, 17590-17599.
[2] V. Paunović, G. Liesche, K. Sundmacher, J. A. van Bokhoven. Nature Catalysis, 2026, 9, 348-362.
[3] S. Teketel, W. Skistad, S. Benard, U. Olsbye, K. P. Lillerud, P. Beato, S. Svelle. ACS Catalysis, 2012, 2, 26-37.