Fabrication of a ZIF-on-lamella-zeolite architecture as a highly efficient catalyst for aldol condensation.

Designing composite catalysts that harness the strengths of individual components while mitigating their limitations is a fascinating yet challenging task in catalyst engineering. In this study, we aimed to enhance the catalytic performance by anchoring ZIF-67 nanoparticles of precise sizes onto lamella Si-MWW zeolite surfaces through a stepwise regrowth process. Co ions were initially grafted onto the zeolite surface using ultrasonication, followed by a seed-assisted secondary growth method. Si-MWW proved to be the ideal zeolite support due to its thin layered structure, large external surface area and substantial lateral dimensions. The abundant Si-OH groups on its surface played a crucial role in securely binding Co ions, limiting size growth and preventing undesirable ZIF-67 aggregation. The resulting ZIF-67/MWW composite with finely dispersed nano-scale ZIF-67 particles exhibited a remarkable catalytic performance and stability in the aldol condensation reactions involving acetone and various aldehydes. This approach holds promise for designing MOF/zeolite composite catalysts.

Seed-Assisted Interzeolite Conversion Strategy for Fabricating Lewis Acid Sn-CHA Zeolites.

Small-pore Lewis acid zeolites have been showing increasing potential in shape-selective reactions regarding small-molecule conversion. In this study, Sn-CHA with tunable framework Sn contents was facilely prepared via a fluoride-free, seed-assisted interzeolite conversion (IZC) pathway. Commercially available dealuminated USY functioned as the parent sample, and seeding played a vital role in accelerating the transformation process, promoting the target zeolite yield, and guiding the attached-growth pathway. Notably, a proto-zeolite phase with a semi-constructed pore structure was captured during the IZC process, which represents a crucial intermediate stage for developing the complete CHA structure and ensuring a well-defined Sn status. The detailed synthesis mechanism was explored in multiscale by a series of techniques. The obtained Sn-CHA and proto-Sn-CHA exhibited excellent catalytic performance in converting 1,3-dihydroxyacetone to methyl lactate. Proto-Sn-CHA was proven to be a highly effective glucose isomerization catalyst owing to its larger pore size and Lewis acidic nature.