3D-printed HZSM-5 and 3D-HZM5@SAPO-34 structured monoliths with controlled acidity and porosity for conversion of methanol to dimethyl either

Abstract

The ability to control the morphology and porosity of zeolite-structured monolith is an important step in the design of zeolite-based catalysts. Herein, additive manufacturing method was used for the rapid synthesis of H-ZSM-5 structured monoliths (3D-HZSM5) with hierarchical porosity (macro-meso-micro) and controlled type and density of acid sites. After 3D-HZSM5 monolith formation, the silicoaluminophosphate (SAPO-34) was grown on the 3D-HZSM5 structured monolith surface via secondary growth method for formation of 3D-HZSM5@SAPO-34 structured monolith. The samples were characterized before and after SAPO-34 growth by XRD, N2 physorption, NH3-TPD, Py-IR and SEM. The characterization results revealed formation of SAPO-34 layer on 3D-HZSM5 structured monolith and also modification also imply that formulation of H-ZSM-5 powder into monolith resulted in slightly less Brønsted acid sites while the density of Lewis acid sites increased. The performance of the 3D-HZSM5 and 3D-HZSM5@SAPO-34 structured monoliths were investigated in catalytic conversion of methanol to dimethyl ether (DME) over a temperature range of 180 to 320 °C for 10 h time on stream. The selectivity to DME was significantly increased as a result of modification in acidity and porosity of the 3D-printed HZSM-5 structured monolith as compared to its powder counterpart and also 3D-HZSM5@SAPO-34 structured monolith. SAPO-34 growth enhanced the density of strong acid sites which caused further conversion of DME to higher hydrocarbons. The highest DME selectivity reached 96% on 3D-HZSM5 structured monolith at 180 °C, which also achieved ~70% conversion of methanol.