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• Small Ni particles exhibit higher steam methane reforming activity than large ones. • The size-dependent activity of Ni catalysts is related to the surface-dependent activity. • Ni(2 1 1) is the most active surface for steam methane reforming. • Decreased Ni(2 1 1) surface fraction results in reduced Ni activity as size increases. Fundamental understanding of the size-dependent activity is essential to harness powers of the nanocatalysts. Here we report an experimental and theoretical study of the Ni particle size effect on activity of steam methane reforming (SMR) to achieve a better understanding of the size dependence of kinetic behavior at an atomic level. A kinetic study illustrated the higher forward methane turnover frequency on the smaller sized Ni particles. The size-dependent activity was well reproduced by microkinetic modeling on a truncated octahedron model with the kinetic parameters estimated by the improved unity bond index-quadratic exponential potential (UBI-QEP) and the Brønsted–Evans–Polanyi (BEP) relationship. Microkinetic modeling suggested that the size-dependent activity of Ni catalysts is associated with the surface-dependent activity. Much higher activity of Ni(2 1 1) than Ni(1 1 1) and Ni(1 0 0) accompanied by decreased Ni(2 1 1) surface fraction results in reduced Ni activity as particle size increases. The activity of Ni(1 1 1) is limited by high free energy barriers, while that of Ni(1 0 0) is limited by site blockage by C* and CH*. This work offers a feasible approach to gain insight into size-dependent activity and to aid rational catalyst design for SMR in which preparing extremely small Ni particles (≤6 nm) might be a good strategy. [ABSTRACT FROM AUTHOR]

• The "dimethylcyclopropane" pathway is dominant for 2-pentene isomerization. • The ring-opening step is the rate-determining step for the isomerization reaction. • Van der Waals interactions would change the scaling relations in zeolite catalysis. Periodic density functional theory (DFT) calculations have been performed to examine the monomolecular reaction mechanism for 2-pentene skeletal isomerization catalyzed by acidic zeolite Beta, Mordenite, and ZSM-5. The use of periodic models allows consideration and analysis of zeolite steric constraints that occur within zeolite microspores. Three different reaction pathways, the "dimethylcyclopropane" (DMCP), methyl shift, and ethyl shift mechanisms, have been considered. The DMCP mechanism which includes rearrangement of protonated cyclopropane is proposed as the dominant reaction pathway, and the ring-opening step determines the overall reaction rate. Comparison of the effective energy barriers for 2-pentene isomerization over the three different zeolites reveals that large 12-ring channels of Beta and MOR have little steric hindrance effect on 2-pentene isomerization while small 10-ring of ZSM-5 significantly increases the reaction activation energy. Calculated results also indicate that the adsorption heat of ammonia is a good descriptor for the reactivity of zeolites without taking into account long-range dispersive forces. In contrast, linear scaling relations cannot be obtained by using the BEEF-vdW functional because van der Waals interactions between zeolites framework and guest molecules affects the energetics of the isomerization reaction and changes the transition state energy scaling relation in zeolite catalysis. [ABSTRACT FROM AUTHOR]

• Novel small-sized mesoporous TS-1 (STS-1) is synthesized by SAC method. • Cost-efficient TPABr is used as template for STS-1 synthesis. • The effect of TPABr concentration of STS-1 is investigated. • The Au/STS-1 catalyst has good performance for propene epoxidation with H 2 /O 2. Designing cost-effective titanium silicalite-1 (TS-1) with enhanced mass transfer ability is of prime scientific and industrial importance. In this work, a novel small-sized mesoporous TS-1 (STS-1) material is first synthesized in cheap TPABr system using steam-assisted crystallization method. Compared with cheap microporous TS-1 prepared by classical hydrothermal method (HTS-1) with particle size of 950 nm, STS-1 shows mesoporous character of 13 nm and reduced average particle size of 590 nm. Moreover, effect of TPABr concentration is systematically investigated, and both of insufficient and overmuch TPABr concentrations are unfavorable because of low crystallinity and exorbitant price, respectively. Importantly, the catalytic performance of cost-effective Au/STS-1 for direct propene epoxidation with H 2 and O 2 is much better than that of Au/HTS-1, and comparable to the performance of the expensive Au/TS-1. By multi-characterizations and activation energy analysis, the underlying mechanism for the enhanced performance is further discussed. This work sheds new light on the design and synthesis of highly effective and cost-efficient TS-1 catalysts. [ABSTRACT FROM AUTHOR]

The dynamic nature of active sites on La-Fe-based perovskites in chemical looping methane oxidation has been studied. According to experimental observations, the reduction of the oxygen carrier is divided into three stages occurring at different active ensembles where the Fe cations are in different coordination environments. The Mars van Krevelen mechanism formulated by microkinetic analysis describes well the effect of oxygen vacancy on the catalytic performance of LaFeO 3. CO 2 is not produced by CO oxidation but rather is a primary product of methane oxidation, and the presence of surface oxygen vacancies would dramatically increase the overall energy barrier for total combustion, thus decreasing the selectivity toward CO 2. Hence, the Fe coordination environment (and hence the oxygen vacancy concentration) is the key parameter governing the catalyst selectivity, in the sense that methane oxidation can vary from total combustion on the O-rich surface to fully selective partial oxidation on the O-deficient surface. [Display omitted] • The dynamic nature of active sites for chemical looping methane oxidation. • The different active ensembles at different reaction stages are identified. • The Fe coordination environment is the key parameter governing the selectivity. • CO 2 is a primary product rather than produced by CO oxidation. • Controlling oxidation time is proposed to achieve methane partial oxidation. [ABSTRACT FROM AUTHOR]

Fischer–Tropsch synthesis of light olefins plays a vital role in the production of major chemical building blocks from non-petroleum resources, having great academic and commercial importance. Herein, Na and S modulated FeMnO x catalysts were employed to systematically investigate the influence of additives, which not only enhanced the CO conversion but also facilitated the olefin formation and suppressed the undesired methane formation. Multiple characterizations confirmed that the existence of promoters would enhance the formation of active species of Fe 5 C 2 at FTO conditions because of the promoted carbon insertion into the iron species from the intermediates dissociation. Combined the steady-state isotopic transient kinetic analysis with dynamic calculation, it confirmed that the promoters indeed had the ability to lower CO activation energy, as well as increase the carbon chain growth activity and the energy barrier to hydrogenation. This study provides a practical strategy for exploring the highly active and stable FTO catalysts. [Display omitted] • Na and S additives over FeMnO x catalyst promoted both the CO conversion and the olefin formation. • Pomotes facilitated the Fe5C2 formation by suppressing the oxidation cycle of iron and enhancing the insertion of carbon. • The presence of promoters reduced the charge of iron and caused more compact bonds of Fe-C, lowing the CO activation energy. • Promoters indeed increased the carbon chain growth activity and the energy barrier to hydrogenation. [ABSTRACT FROM AUTHOR]

• An ion exchange based strategy was used to synthesize the hierarchy structured mutimetal MOFs derived electrocatalyst. • This strategy prevents the collapse of well-designed MOF nanostructures during the air calcination process. • The unique electronic modulation of Co-Ni-Fe in spinel oxides can optimize the binding strength of OER intermediates. • CoNiFeO x -NC catalyst delivers highly efficient OER performance (η 50 = 265 mV). Metal-organic frameworks (MOFs) have recently emerged as promising precursors to construct efficient non-noble metal electrocatalyst for oxygen evolution reaction (OER). Herein, a Co-Ni-Fe spinel oxide-carbonitrides hybrids (CoNiFeO x -NC) electrocatalyst with hierarchical structure was synthesized from Fe-MIL-101-NH 2 through a unique ion-exchange based strategy. The ion exchange of Fe-MIL-101-NH 2 with both Ni and Co ions induced a hierarchically structured 2-D ternary metal MOF shell layer encapsulated 3-D octahedral MOF crystals as a core. This prevents the collapse of MOF frameworks during the air calcination process and affords highly porous structure and large surface area. Additionally, the unique combination of Co-Ni-Fe in spinel oxides derived from calcination of the hierarchically structured core-shell MOF provides a favorable electronic environment for the adsorption of OER intermediates, which was further verified by the XPS characterizations and DFT calculations. DFT study revealed the Ni-Co coordinated O h sites in the MFe 2 O 4 reverse spinel structures as the main active sites, which tuned the binding strength of oxygen species with a catalyst through electron transfer of Fe→Co→Ni, thereby lowered the energy barriers for OER. As a result, the rationally designed CoNiFeO x -NC catalyst manifests superior OER performance with a low overpotential of 265 mV at 50 mA cm−2 and a decent Tafel slope of 64.1 mV dec-1. The ion-exchange based strategy may serve as a versatile platform for rational design and synthesis of multi-metallic MOF derived electrocatalysts. [ABSTRACT FROM AUTHOR]

We successfully realized the directional construction of Pt-Mn 2 O 3 interfacial sites (by the combination of in-situ doping and impregnation methods) to boost selective oxidation of ethylene glycol under mild conditions. It is found that the pre-distribution of Mn 2 O 3 inside support unexpectedly induced the formation of Pt-Mn 2 O 3 interfacial active sites with strong electron coupling effect, leading to an unprecedented glycolic acid oxidation activity (turnover frequency: 3196.9 h−1) and glycolic acid yield (86.4 %). • Enhanced catalytic performance of ethylene glycol oxidation was achieved. • Strong electron coupling effect was revealed in the Pt-Mn interface. • Quantitative analysis of the intrinsic active sites was performed. • The promotion role of Pt-Mn interfacial on reaction mechanism was correlated. Rational design of desirable active sites is still a grand challenge for the efficient conversion of polyols to value-added products. Herein, we successfully constructed the Pt-Mn 2 O 3 interfacial sites rather than Pt-MnO x solid solution to boost selective oxidation of ethylene glycol to glycolic acid under mild conditions. X-ray absorption spectroscopy and high-resolution transmission electron microscope revealed that the pre-distribution of Mn 2 O 3 inside support unexpectedly induced the formation of Pt-Mn 2 O 3 interfacial active sites with strong electron coupling effect, leading to an unprecedented catalytic activity (turnover frequency: 3196.9 h−1) and glycolic acid yield (86.4 %). In addition, quantitative analysis of the intrinsic active sites was performed, and a "volcano-shape" relationship was established between initial reaction rate and Pt/Mn ratio. Moreover, the structure-dependent reaction kinetics and density functional theory calculation revealed that the synergistic effect between the Mn 2 O 3 redox cycle and Pt promotes the adsorption of ethylene glycol and the activation of C H bond, resulting in the lower activation energy of ethylene glycol oxidation. The outcome of this work offers a promising avenue for the direct construction of efficient Pt-based catalysts with desired active sites. [ABSTRACT FROM AUTHOR]

• High selectivity of core-shell alloy catalysts for propane dehydrogenation. • Linear scaling relations are established to identify the descriptor. • Microkinetic modeling is carried out to obtain turnover frequency. • Co@Pt is the best catalyst by making a compromise between activity and selectivity. Microkinetic analysis combined with the results obtained from density functional theory calculations has been performed to examine the catalytic activity and selectivity of Pt-based core-shell alloy catalysts for propane dehydrogenation. Calculated results indicate that substitution of 11 late transition metals for the core region of Pt nanoparticles would significantly modify the electronic structure of the surface Pt atoms through the strain effect and charge transfer. The core-shell catalysts are found to have less negative propylene adsorption energies and higher activation energies for the dehydrogenation reactions than Pt, thus giving rise to a lower catalytic activity and a higher selectivity toward propylene. Linear chemisorption energy and transition state energy scaling relations hold very well in the present work, and the adsorption energy of propylene is identified to be a good descriptor to represent the overall kinetics. The scaling relations also suggest that a higher catalyst selectivity toward propylene can only be achieved at the expense of a lower catalytic activity for propane dehydrogenation. If a compromise is made between catalytic activity and catalyst selectivity, Co@Pt is proposed to be the best core-shell catalyst for propane dehydrogenation. [ABSTRACT FROM AUTHOR]