Theoretical investigation of the olefin cycle in H-SSZ-13 for the ethanol-to-olefins process using ab initio calculations and kinetic modeling

The formation of the hydrocarbon pool (HCP) in the ethanol-to-olefins (ETO) process catalyzed by H-SSZ-13 is studied in a kinetic model with ab initio computed reaction barriers.

First-principles microkinetic analysis of Lewis acid sites in Zn-ZSM-5 for alkane dehydrogenation and its implication to methanol-to-aromatics conversion

Stabilities and dehydrogenation activities of butane and cyclohexane on four different Zn sites in ZSM-5 zeolite were theoretically revealed. ZnOH⁺ was identified as the most active site at low temperature and the activity increases with the sequence of dehydrogenation.

First-principles microkinetic simulations revealing the scaling relations and structure sensitivity of CO2 hydrogenation to C1 & C2 oxygenates on Pd surfaces

CO₂ hydrogenation to alcohols and other oxygenates on Pd(211) and Pd(111) surfaces was studied by microkinetic modelling. Energy scaling relations on two surfaces were established. Activity plots as a function of reaction conditions were identified.

How Accurately Do Approximate Density Functionals Predict Trends in Acidic Zeolite Catalysis?

Density functional theory (DFT) is increasingly used for computational screening procedures with the aim of finding new catalysts. To achieve this, it is critical that relative differences between materials are predicted with high accuracy. How DFT at the generalized gradient approximation (GGA) level performs in this respect is investigated here for catalytic reactions employing acidic zeotypes using highly accurate DLPNO-CCSD(T) calculations as the reference. This is studied for 65 reaction energies and 130 reaction barriers related to zeolite catalysis. Our results obtained for the PBE-D3 and BEEF-vdW functionals show that while these functionals are prone to large errors, they predict trends occurring from one catalyst to another with an accuracy of about 5 kJ/mol, strongly supporting the widespread use of DFT calculations for the computational screening and design of new catalytic materials.

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.