Influence of Diffusion and Acid Properties on Methane and Propane Selectivity in Methanol-to-Olefins Reaction

Unravelling the Crucial of Spatial Al Distribution to Realize Precise Alkali-Treatment for Target Acid-Catalyzed Reactions

Constructing mesoporous structure within zeolites by alkali-treatment is an effective protocol to improve their diffusion properties. However, undesirable changes in Brönsted acid site (BAS) densities always offset this advantage in acid-catalyzed reactions. In this context, the crucial roles of spatial aluminum (Al) distribution were unraveled during alkali-treatment of MFI zeolite and the desirable BAS density was achieved in obtained hierarchical samples for the target reactions. Various characterization methods, particularly the multiple one- and two-dimensional magic-angle spinning (MAS) NMR techniques, were performed to track the alkali-treatment processes. For the sample with a more uniform spatial Al distribution, more tetrahedral Al sites would fall off and migrate around the Si-OH in zeolite as Al(OH)4 -. Those re-deposited Al(OH)4 - sites were easily transformed into NMR-invisible Al sites during the calcination process, which contributed negligibly to both Brönsted and Lewis acidities, thus being referred to "acid-free" Al species. While most tetrahedral Al sites were preserved after the alkali-treatment of sample with non-uniform Al distribution and the BAS density gradually increased with treatment time. According to the requirements of typical acid-catalyzed reactions, such as catalytic cracking of 1,3,5-triisopropylbenzene and methanol-to-olefins, the desired hierarchical zeolite catalysts were developed by matching the amounts of extracted Si and generated "acid-free" Al during the precise alkali-treatment.

Unlocking Enhanced Butadiene Selectivity: The Crucial Role of Zeolite Channel Confinement in the Selective Decarbonylation of γ-Valerolactone

Herein, we report a highly selective production route for butadiene from γ-valerolactone over zeolite catalysts. The catalytic performance of eight zeolites with different framework topologies were compared, revealing that zeolites with narrower 10-membered ring channels exhibit enhanced selectivity of butadiene. Specifically, ZSM-35 and ZSM-22, featuring the narrowest 10-membered ring channels, demonstrate the highest butadiene selectivity to 61 % and 59 %, respectively. Notably, surface passivation of ZSM-35 leads to a remarkable increase in butadiene selectivity to 82 %, maintaining a 99 % conversion. Additionally, we propose a reaction network and identify cyclopentenone as a key intermediate in the transformation of γ-valerolactone to butadiene. Both experimental and theoretical results conclude that confinement effect of 10-membered ring channels improves the selectivity of butadiene.

Water-Stable Microporous Bipyrazole-Based Framework for Efficient Separation of MTO Products

Recently, methanol-to-olefins (MTO) technology has been widely used. The development of new adsorbents to separate MTO products and obtain high-purity ethylene (C2H4) and propylene (C3H6) has become an urgent task. Herein, an exceptionally highly water-stable metal-organic framework (MOF), [Cu3(OH)2(Me2BPZ)2]·(solvent)x (1) (H2Me2BPZ = 3,3'-dimethyl-1H,1'H-4,4'-bipyrazole) with hexagonal pores, has been elaborately designed and constructed. After being soaked in water for 7 days, it still maintains its structure, and the uptake of N2 at 77 K is unchanged. The adsorption capacity of C3H6 can reach 138 cm3 g-1, while the uptake of C2H4 is only 52 cm3 g-1 at 298 K and 1 bar. The dynamic breakthrough experiments show that the mixture of C3H6/C2H4 (50/50, v/v) can be efficiently separated in one step. High-purity C2H4 and C3H6 can be obtained through an adsorption and desorption cycle and the yields of C2H4 (purity ≥ 99.95%) and C3H6 (purity ≥ 99%) are 84 and 48 L kg-1, respectively. Surprisingly, when the flow rate is increased, the separation performance has no obvious change. Additionally, humidity has no effect on the separation performance. Finally, theoretical simulations indicate that there are stronger interactions between the C3H6 molecule and the framework, which are beneficial to capturing C3H6 over C2H4.

Unique Role of GeO2 as a Noninvasive Promoter of Nano-Sized Zeolite Crystals

The synthesis of zeolites with nano-sized dimensions is often limited to a narrow design space that conventionally relies upon the design of organics to direct hierarchical materials. Here, it is demonstrated that the addition of an inorganic modifier, germanium oxide (GeO₂ ), to a zeolite growth mixture directs the formation of crystals with ultrasmall dimensions. This effect is observed for zeolites ZSM-11 and ZSM-5 over a range of synthesis conditions wherein the role of GeO₂  in zeolite crystallization deviates from its typical function as a heteroatom. Notably, the final products contain trace amounts of Ge, which indicates the inorganic modifier does not compete for sites in the zeolite framework based on its formation of a discrete phase that enables GeO₂  recovery. Catalytic tests using the methanol-to-hydrocarbons reaction reveal significant enhancement in the performance of zeolite catalysts prepared with GeO₂  compared to reported examples of nano-sized zeolites. These findings highlight a potentially generalizable and commercially viable synthesis method to reduce mass-transport limitations in zeolites for diverse applications.

Effect of ZSM-5 zeolite porosity on catalytic cracking of n-heptane

The selectivity of ethylene and propylene in cracking of n-heptane is connected to the micropore to mesopore ratioof ZSM-5 structure.