Although perovskites have been widely used in catalysis, tuning of their surface termination to control reaction selectivity has not been well established. In this study, we employed multiple surface-sensitive techniques to characterize the surface termination (one aspect of surface reconstruction) of SrTiO (STO) after thermal pretreatment (Sr enrichment) and chemical etching (Ti enrichment). We show, by using the conversion of 2-propanol as a probe reaction, that the surface termination of STO can be controlled to greatly tune catalytic acid/base properties and consequently the reaction selectivity over a wide range, which is not possible with single-metal oxides, either SrO or TiO . Density functional theory (DFT) calculations explain well the selectivity tuning and reaction mechanism on STO with different surface termination. Similar catalytic tunability was also observed on BaZrO , thus highlighting the generality of the findings of this study.

Methane conversion has received renewed interest due to the rapid growth in production of shale gas. Methane combustion for power generation and transportation is one of the alternatives for methane utilization. However, complete conversion of methane is critical to minimize negative environmental effects from unburned methane, whose noxious effect is 25 times greater than that of CO 2 . Although perovskite catalysts have high thermal stability, their low activities for methane combustion prevent them from being utilized on a commercial basis. In this work, we show the impact from reconstruction of surface and subsurface monolayers of perovskite catalysts on methane combustion, using SrTiO 3 (STO) as a model perovskite. Several STO samples obtained through different synthetic methods and subjected to different postsynthetic treatments were tested for methane combustion. Through top surface characterization, kinetic experiments (including isotope labeling experiments) and density functional theory calculations, it is shown that both surface segregation of Sr and creation of step surfaces of STO can impact the rate of methane combustion over an order of magnitude. This work highlights the role of surface reconstruction in tuning perovskite catalysts for methane activation.

The construction of a computational framework that describes the kinetic details of the propylene oligomerization reaction network on Brønsted acidic zeolites is particularly challenging due to the considerable number of species and reaction steps involved in the mechanism. This work presents a detailed microkinetic model at the level of elementary steps that includes 4243 reactions and 909 ionic and molecular species within the C2–C9 carbon number range. An automated generation procedure using a set of eight reaction families was applied to construct the reaction network. The kinetic parameters for each elementary step were estimated using transition state theory, Evans–Polanyi relationships, and thermodynamic data. The reaction mechanism and its governing kinetic parameters were embedded into the design equation of a plug-flow reactor, which was the reactor configuration used to experimentally measure reactant and product concentrations as a function of propylene conversion and temperature on a representative H-ZSM-5 (MFI) zeolite. The resulting mechanistic model is able to accurately describe the experimental data over a wide range of operating conditions in the low propylene conversion (<4%) regime. The agreement between experimentally measured propylene conversion and product selectivities and the model results demonstrates the robustness of the model and the approach used to develop it to simulate the kinetic behavior of this complex reaction network.

Brønsted acid zeolites catalyze alkene oligomerization to heavier hydrocarbon products of varied size and branching. Propene dimerization rates decrease monotonically with increasing crystallite size for MFI zeolites synthesized with fixed H+-site density, revealing the strong influence of intrazeolite transport limitations on measured rates, which has gone unrecognized in previous studies. Transient changes in dimerization rates upon step-changes in reactant pressure (150–470 kPa C3H6) or temperature (483–523 K) reveal that intrazeolite diffusion limitations become more severe under reaction conditions that favor the formation of heavier products. Together with effectiveness factor formalisms, these data reveal that product and reactant diffusion, and consequently oligomerization rates and selectivity, are governed by the composition of hydrocarbon products that accumulate within zeolitic micropores during alkene oligomerization. This occluded organic phase strongly influences rates and selectivities of alkene oligomerization on medium-pore zeolites (MFI, MEL, TON). Recognizing the coupled influences of kinetic factors and intrazeolite transport limitations imposed by occluded reaction products provides opportunities to competently tailor rates and selectivity in alkene oligomerization and other molecular chain-growth reactions through judicious selection of zeolite topology and reaction conditions.

Strong metal−support interactions (SMSIs) and catalyst deactivation have been heavily researched for decades by the catalysis community. The promotion of SMSIs in supported metal oxides is commonly associated with H 2 treatment at high temperature (>500 °C), and catalyst deactivation is commonly attributed to sintering, leaching of the active metal, and overoxidation of the metal, as well as strong adsorption of reaction intermediates. Alcohols can reduce metal oxides, and thus we hypothesized that catalytic conversion of alcohols can promote SMSIs in situ. In this work we show, via IR spectroscopy of CO adsorption and electron energy loss spectroscopy (EELS), that during 2-propanol conversion over Pd/TiO 2 coverage of Pd sites occurs due to SMSIs at low reaction temperatures (as low as ∼190 °C). The emergence of SMSIs during the reaction (in situ) explains the apparent catalyst deactivation when the reaction temperature is varied. A steady-state isotopic transient kinetic analysis (SSITKA) shows that the intrinsic reactivity of the catalytic sites does not change with temperature when SMSI is promoted in situ; rather, the number of available active sites changes (when a TiO x layer migrates over Pd NPs). SMSI generated during the reaction fully reverses upon exposure to O 2 at room temperature for ∼15 h, which may have made their identification elusive up to now.