Hydrocarbon Products Occluded within Zeolite Micropores Impose Transport Barriers that Regulate Brønsted Acid-Catalyzed Propene Oligomerization

Influence of aluminum zoning toward external surfaces in MFI zeolites on propene oligomerization catalysis

Brønsted acid zeolites catalyze alkene oligomerization reactions, an important route to produce fuels and chemicals from light hydrocarbon feedstocks. Propene dimerization rates (per H+, 503 K) decrease monotonically with increasing crystallite size in MFI zeolites because heavy oligomer products remain occluded within microporous voids and restrict intrazeolite diffusion of reactants and products. Here, we show that the preferential zoning of framework Al centers and their associated H+ sites toward exterior surfaces of MFI crystallites in an "egg-shell" architecture minimizes the extent of diffusion-enhanced secondary reactions within a given crystallite, which increases both propene dimerization rates (per H+) and selectivity to true oligomer products. These results show that tailoring Al distributions to be spatially zoned toward external surfaces of medium-pore zeolite crystallites is efficacious at minimizing diffusion path lengths to increase alkene oligomerization rates and selectivity to true oligomer products.

Preparation of food active packaging materials based on calcium hydroxide and modified porous medium for reducing carbon dioxide and kimchi odor

Carbon dioxide and kimchi odor compounds, formed during fermentation, negatively affect the long-distance distribution of commercial kimchi. To address these issues, in this study, we modified different porous media (activated carbon, bleaching earth, diatomite, and zeolite) using sodium bicarbonate and silver (Ag) ions. Functional sheets were prepared using linear low-density polyethylene, calcium hydroxide, a porous medium, and a blowing agent. Various prepared porous media and sheets were effective in removing acetic acid, sulfur compounds (allyl methyl sulfide, dimethyl disulfide, allyl methyl disulfide, and diallyl disulfide), and carbon dioxide. Porous media with micropores exhibited a sulfur compound removal efficiency of 43.5%-99.4%, while no effect was observed on acetic acid removal. However, porous media with mesopores showed an acetic acid removal efficiency of 42.3%-90.7%, with no reduction in sulfur compounds removal. The impregnation of porous materials with sodium bicarbonate significantly (p < 0.05) enhanced the acetic acid removal activity. Ag modification improved the sulfur compound removal of the mesoporous bleaching earth and diatomite statistically (p < 0.05). Additionally, the incorporation of sodium bicarbonate-impregnated mesoporous media significantly improved carbon dioxide removal, reducing concentrations from 25.97% to 14.27% with respect to the control group. Our functional food packaging materials can solve the current issues in kimchi distribution by removing carbon dioxide and kimchi odor without affecting its quality. PRACTICAL APPLICATION: Food active packaging materials containing calcium hydroxide and modified porous medium are effective in removing carbon dioxide and kimchi odor (acetic acid and sulfur compounds). The removal of carbon dioxide and kimchi odor, which adversely affect the distribution and sale of commercial kimchi, can help solve the current issues with kimchi distribution without affecting its quality.