Hydrothermal Annealing of Hierarchical ZSM-5 Zeolites Improves Catalytic Performance.

Engineering next-generation zeolite catalysts requires state-of-the-art synthesis techniques to tailor the properties of materials along with robust methods to evaluate their catalytic performance. Here, we introduce hydrothermal annealing as a facile and highly effective method to improve the activity and lifetime of zeolite catalysts. This post-synthesis treatment uses a siliceous growth solution at approximate solubility of zeolite crystals with high temperature to alter the physicochemical properties of as-synthesized materials. We employ the methanol-to-hydrocarbons (MTH) process as a benchmark reaction, along with a wide range of characterization techniques, to assess the impact of annealing on four nanosized and hierarchical ZSM-5 materials compared to a commercial sample. Our findings reveal that annealing significantly increased cumulative MTH turnover without appreciably altering product selectivity, despite non-obvious changes to zeolite structure as a result of the annealing process. Comparisons of catalyst performance are made under identical reaction conditions using a descriptor that correlates cumulative turnovers to compositional, mass transport, and textural properties of each material - in line with growing efforts to increase rigor and reproducibility in the field of catalysis. The collective approach used in this study serves as a guideline for establishing structure-composition-performance relationships for zeolite-based catalysts across wide-ranging applications.