Influence of brønsted-acid and cation-exchange sites on ethene adsorption in ZSM-5

DFT based microkinetic modeling of confinement driven [4 + 2] Diels–Alder reactions between ethene and isoprene in H-ZSM5

“…3a). Consistent with other studies, 46,48 the Brønsted proton is attracted to the center of the π-bond of ethene. The formation of this physisorbed structure is exergonic, with a Gibbs free energy of −15(−27) (kJ mol −1 ).…”

“…PAW potentials 42 with generalized gradient approximation (GGA) using the Perdew-Burke-Ernzerhof (PBE) 43 exchange correlation functional with Grimme-D2 (DFT-D2) 44,45 dispersion corrections were used in view of their accuracy for small adsorbates in other zeolites. 39,46 The convergence criterion for electronic relaxation was 10 −4 eV with a plane-wave energy cutoff of 400 eV; the ionic convergence was set with the criteria that the force on each ion be smaller than 0.02 eV Å −1 . Gaussian smearing with width 0.1 eV was used; all energies were extrapolated to 0 K. Transition states were identified by using the climbing image nudge elastic band method (NEB) 47 with seven images between the reactants and product.…”

“…In a separate study, 46 we assessed the interactions between the π-bond of ethene and the active sites of Brønsted Fig. 3 The most energetically stable adsorption configurations of our reactants.…”

Existence and Properties of Isolated Catalytic Sites on the Surface of β-Cristobalite-Supported, Doped Tungsten Oxide Catalysts (WOx/β-SiO2, Na-WOx/β-SiO2, Mn-WOx/β-SiO2) for Oxidative Coupling of Methane (OCM): A Combined Periodic DFT and Experimental Study

“…In particular, different molecular geometries of the active WO x surface sites exhibit different catalytic properties. − The active surface sites present on the support can be isolated, dimeric, oligomeric, or polymeric, which ultimately influences the resulting activity/selectivity and reaction mechanism. ,− The structure of the active site typically depends on its surface coverage with the maximum amount that can be anchored in a two-dimensional fashion on the support without forming a three-dimensional crystalline phase, defined as the monolayer coverage. The monolayer coverage is routinely used to assess the overall catalyst activity/selectivity of well-defined surface sites. ,− …”

Influence of Substrate Concentration on Kinetic Parameters of Ethanol Dehydration in MFI and CHA Zeolites and Relation of These Kinetic Parameters to Acid–Base Properties

“…The observed shift of the TPSR temperature maximum to higher temperatures for this sample compared to the CHA samples shows that the higher ethanol dehydration activity of the CHA samples cannot be attributed to the energetic effect but rather to the entropic part of the kinetic rate constant. As the published experimental values of the ethylene adsorption energy on the H-MFI zeolite [55,56] are in the range of 31-39 kJ•mol −1 , only weak interaction of ethylene with the zeolite framework can be expected, and hence obtained values of the apparent activation energy can be attributed solely to the kinetics of adsorbed ethanol transformation. According to Alexopoulos et al [57], the value of apparent activation energy 118 kJ•mol −1 for ethanol dehydration over MFI type zeolite can be attributed to the third step of associative type reaction mechanism (A2 in [57]).…”