The role of decarboxylation reactions during the initiation of the methanol-to-olefins process

The mechanism for direct Csingle bondC bond formation during the initiation of the methanol-to-olefins (MTO) process is still under discussion. Carbon dioxide formation is often observed during initiation, but there are only few investigations into the role of decarboxylation. We investigate decarboxylation pathways in the H-SSZ-13 zeolite from methanol to olefins via direct carbon–carbon coupling. Additionally, the rate-determining steps were recomputed in the H-ZSM-5 and H-SAPO-34 zeolite. Gibbs free energy barriers were calculated using periodic density functional theory in combination with CCSD(T) calculations on cluster models. For H-SSZ-13, kinetic batch reactor simulations were performed. We found for H-SSZ-13 that pathways via decarboxylation reactions are equally likely as previously computed pathways including decarbonylation mechanisms (also known as ketene or CO pathway). Lactones formed from ketenes and formaldehyde were identified as the main intermediates. The decarboxylation mechanism has similar barriers in H-SSZ-13, H-ZSM-5, and H-SAPO-34, while the barriers for methylation and decarbonylation reactions are significantly lower in H-ZSM-5 and higher in H-SAPO-34. Decarboxylation reactions of lactones could explain experimentally detected carbon dioxide during the initial phase of the MTO process

Templated encapsulation of platinum-based catalysts promotes high-temperature stability to 1,100 °C

Stable catalysts are essential to address energy and environmental challenges, especially for applications in harsh environments (for example, high temperature, oxidizing atmosphere and steam). In such conditions, supported metal catalysts deactivate due to sintering-a process where initially small nanoparticles grow into larger ones with reduced active surface area-but strategies to stabilize them can lead to decreased performance. Here we report stable catalysts prepared through the encapsulation of platinum nanoparticles inside an alumina framework, which was formed by depositing an alumina precursor within a separately prepared porous organic framework impregnated with platinum nanoparticles. These catalysts do not sinter at 800 °C in the presence of oxygen and steam, conditions in which conventional catalysts sinter to a large extent, while showing similar reaction rates. Extending this approach to Pd-Pt bimetallic catalysts led to the small particle size being maintained at temperatures as high as 1,100 °C in air and 10% steam. This strategy can be broadly applied to other metal and metal oxides for applications where sintering is a major cause of material deactivation