A theoretical study of nitric oxide adsorption and dissociation on copper-exchanged zeolites SSZ-13 and SAPO-34: the impact of framework acid-base properties

The influence of adjacent Al atoms on the hydrothermal stability of H-SSZ-13: a first-principles study

The Al concentration and distribution have a great influence on the hydrothermal stability of the H-SSZ-13 zeolites in experiments. In this work, first-principles calculations are performed to clarify the decomposition mechanism of an H-SSZ-13 framework with adjacent Al atom pair distribution under hydrothermal conditions. It is found that the adjacent Al atoms have a tendency to occupy the para-sites of the 4-membered rings (4MRs) in the framework. Water molecules are chemisorbed onto the Al atom one by one, and the hydroxylation of the neighboring O atoms induces the breaking of the Al-O bonds, which causes the first dealumination in 4MRs. The other Al atom in the para-site can be easily removed from the framework once the first one is lost. The feasible subsequent dealumination of adjacent Al atoms would break the linker of 6MRs in the framework, which is responsible for the degraded hydrothermal stability. Moreover, the partial substitution of metal ions (such as Na⁺ and Cu⁺) for the protons in the framework will greatly stabilize the Al-O bonds and enlarge the energy barrier of para-site Al dealumination, which leads to the improved hydrothermal stability of H-SSZ-13.

Effect of Water Molecule on Photo-Assisted Nitrous Oxide Decomposition over Oxotitanium Porphyrin: A Theoretical Study

Water vapor has generally been recognized as an inhibitor of catalysts in nitrous oxide (N2O) decomposition because it limits the lifetime of catalytic reactors. Oxygen produced in reactions also deactivates the catalytic performance of bulk surface catalysts. Herein, we propose a potential catalyst that is tolerant of water and oxygen in the process of N2O decomposition. By applying density functional theory calculations, we investigated the reaction mechanism of N2O decomposition into N2 and O2 catalyzed by oxotitanium(IV) porphyrin (TiO-por) with interfacially bonded water. The activation energies of reaction Path A and B are compared under thermal and photo-assisted conditions. The obtained calculation results show that the photo-assisted reaction in Path B is highly exothermic and proceeds smoothly with the low activation barrier of 27.57 kcal/mol at the rate determining step. The produced O2 is easily desorbed from the surface of the catalyst, requiring only 4.96 kcal/mol, indicating the suppression of catalyst deactivation. Therefore, TiO-por is theoretically proved to have the potential to be a desirable catalyst for N2O decomposition with photo-irradiation because of its low activation barrier, water resistance, and ease of regeneration.