Strengthening catalytic synergy of two function-complementary ZSM-5 by optimizing their spatial organizations in fixed-bed reactor to boost methanol aromatization

Abstract

The effect of proximity of two different SiO 2 /Al 2 O 3 ratio ZSM-5 catalysts with complementary acidic properties on their catalytic synergy over methanol stepwise aromatization was specifically studied based on a series of different packing modes. The results showed that the powder mixing mode with high proximity excessively enhanced the synergy by intensifying mass transfer between two catalysts. Although it presented a high aromatics selectivity of 57.2%, but the catalyst lifetime was only 10 h due to the intense reverse of polymethylbenzene. The granule mixing mode with larger particle size only slightly improved the catalyst lifetime. Packing two ZSM-5 catalysts in separated dual beds mode could prolong the lifetime to 157 h but the aromatics selectivity was reduced to 21.0%, indicating that low proximity is not favored the catalytic synergy. Interestingly, the suitable proximity of designed alternative sequence beds mode not only intensified intermediates transport to some extent but also relieved the negative influence of aromatic reversion. The moderate synergy remarkably increased the aromatics selectivity to 28.9% with a satisfactory lifetime of 117 h. This work preliminarily elucidates the effect of proximity determined by the spatial organization of double ZSM-5 catalysts on their catalytic synergy for methanol aromatization. Packing Zn/Z-60 and NZ-500 in alternating sequence beds (packing mode) in the tubular fixed bed observably prolonged catalytic lifetime with a satisfied aromatics selectivity. • The effect of proximity on catalytic synergy of double ZSM-5 for MTA was studied. • The catalyst proximity was precisely regulated based on eight packing modes. • Enhanced mass transfer for aromatization was achieved under high proximity. • Catalytic stability was increased by decreasing catalyst proximity. • Mild catalyst proximity over alternate beds enhanced catalytic synergy for MTA.