Ji Su

The breaking of translational symmetry at oxide surfaces gives rise to coordinatively unsaturated cations/anions and surface restructuring—key factors that govern surface reactivity. Using direct in situ environmental transmission electron microscopy (TEM) observations along with atomistic modeling, we report oscillatory redox behavior in CuO under H ₂ , where cyclic surface reconstruction and reactivity modulation occur via the Mars–van Krevelen (MvK) mechanism. We observe self-switching between oxygen-rich and oxygen-deficient surface reconstructions, alternately activating and deactivating the surface for H ₂ O formation. During periods of chemical inactivity, the oxygen-deficient surface undergoes slow reoxidation via lattice oxygen diffusing from subsurface and bulk reservoirs, restoring the active oxygen-rich surface termination. The inherent disparity in chemical activity among undercoordinated surface ions, along with sluggish subsurface-to-surface oxygen replenishment, drives this oscillatory redox cycle, modulating H ₂ -induced loss of lattice oxygen at the surface and its delayed replenishment from the subsurface. This creates spatiotemporally separated redox steps at the oxide surface. The phenomena and atomistic insights presented here have significant implications for manipulating the surface reactivity of oxides by tuning the separation of these redox steps.

Single-atom site catalysts can improve the rates and selectivity of many catalytic reactions. We have modified Pt ₁ /CeO ₂ single sites by combining them with molecular groups and with oxygen vacancies of the support. The new sites include hydrided (Pt ²⁺ -Ce ³⁺ H ^δ− ) and hydroxylated (Pt ²⁺ -Ce ³⁺ OH) sites that exhibit higher reactivity and selectivity to previous single sites for several reactions, including a ninefold increase in the reaction rate for carbon monoxide oxidation and a 2.3-fold improvement of propylene selectivity for oxidative dehydrogenation of propane. The atomic structure and reaction steps of these sites were determined with in situ and ex situ spectroscopy techniques and theoretical methods.

Direct methane conversion to liquid fuels or value-added chemicals is a promising technology to utilize natural resources without resorting to further petroleum extraction. However, discovering efficient catalysts for this reaction is challenging due to either coke formation or unfavorable C-H bond activation. Here, we design single atom alloy (SAA) catalysts to simultaneously eliminate the above two bottlenecks based on mechanism-guided strategies: (1) active single atom enables favorable C-H bond breaking, and (2) less reactive host metal facilitates C-C coupling and thus avoids strong binding of carbonaceous species. Employing electronic structure theory calculations, we screened stability of multiple SAAs with 3d-5d transition metals atomically dispersed on a copper surface in terms of avoiding dopant aggregation and segregation. We then evaluated reactivities of the stable SAAs as catalysts for direct methane conversion to C2 products, including methane dehydrogenation and C-C coupling mechanisms. Combining selectivity analysis with kinetic modeling, we predicted that nickel dispersed on copper, i.e., Ni/Cu SAA, is a highly active and selective catalyst that can efficiently transform methane to ethylene. This work designs efficient SAA catalysts for direct methane activation and provides chemical insights into engineering compositions of SAAs to tune their catalytic performances.

Cobalt is an efficient catalyst for Fischer−Tropsch synthesis (FTS) of hydrocarbons from syngas (CO + H₂) with enhanced selectivity for long-chain hydrocarbons when promoted by Manganese. However, the molecular scale origin of the enhancement remains unclear. Here we present an experimental and theoretical study using model catalysts consisting of crystalline CoMnO_x nanoparticles and thin films, where Co and Mn are mixed at the sub-nm scale. Employing TEM and in-situ X-ray spectroscopies (XRD, APXPS, and XAS), we determine the catalyst’s atomic structure, chemical state, reactive species, and their evolution under FTS conditions. We show the concentration of CH_x, the key intermediates, increases rapidly on CoMnO_x, while no increase occurs without Mn. DFT simulations reveal that basic O sites in CoMnO_x bind hydrogen atoms resulting from H₂ dissociation on Co⁰ sites, making them less available to react with CH_x intermediates, thus hindering chain termination reactions, which promotes the formation of long-chain hydrocarbons.

Developing a desirable ethanol dehydrogenation process necessitates a highly efficient and selective catalyst with low cost. Herein, we show that the “complex active site” consisting of atomically dispersed Au atoms with the neighboring oxygen vacancies (Vo) and undercoordinated cation on oxide supports can be prepared and display unique catalytic properties for ethanol dehydrogenation. The “complex active site” Au−Vo−Zr³⁺ on Au₁/ZrO₂ exhibits the highest H₂ production rate, with above 37,964 mol H₂ per mol Au per hour (385 g H₂ h⁻¹) at 350 °C, which is 3.32, 2.94 and 15.0 times higher than Au₁/CeO₂, Au₁/TiO₂, and Au₁/Al₂O₃, respectively. Combining experimental and theoretical studies, we demonstrate the structural sensitivity of these complex sites by assessing their selectivity and activity in ethanol dehydrogenation. Our study sheds new light on the design and development of cost‐effective and highly efficient catalysts for ethanol dehydrogenation. Fundamentally, atomic‐level catalyst design by colocalizing catalytically active metal atoms forming a structure‐sensitive “complex site”, is a crucial way to advance from heterogeneous catalysis to molecular catalysis. Our study advanced the understanding of the structure sensitivity of the active site in atomically dispersed catalysts.

Developing a desirable ethanol dehydrogenation process necessitates a highly efficient and selective catalyst with low cost. Herein, we show that the “complex active site” consisting of atomically dispersed Au atoms with the neighboring oxygen vacancies (Vo) and undercoordinated cation on oxide supports can be prepared and display unique catalytic properties for ethanol dehydrogenation. The “complex active site” Au−Vo−Zr³⁺ on Au₁/ZrO₂ exhibits the highest H₂ production rate, with above 37,964 mol H₂ per mol Au per hour (385 g H₂ h⁻¹) at 350 °C, which is 3.32, 2.94 and 15.0 times higher than Au₁/CeO₂, Au₁/TiO₂, and Au₁/Al₂O₃, respectively. Combining experimental and theoretical studies, we demonstrate the structural sensitivity of these complex sites by assessing their selectivity and activity in ethanol dehydrogenation. Our study sheds new light on the design and development of cost‐effective and highly efficient catalysts for ethanol dehydrogenation. Fundamentally, atomic‐level catalyst design by colocalizing catalytically active metal atoms forming a structure‐sensitive “complex site”, is a crucial way to advance from heterogeneous catalysis to molecular catalysis. Our study advanced the understanding of the structure sensitivity of the active site in atomically dispersed catalysts.

Single-atom catalysts (SACs) featuring 100% atom utilization and uniform isolated active sites have been receiving sustainable attention over the last decade, as they offer exceptional performance in various catalytic applications. The motivation behind studying SACs is to develop highly active, selective, and stable catalysts for industrial applications with desirable economic and ecological benefits. Despite their promising potential, SACs face challenges related to stability, which need to be addressed for practical implementation. In this mini-review we discuss the existing stability issues of SACs, and summarize the deactivation mechanism and behaviors, protective strategies, and regeneration methods of SACs. We highlighted the challenges and prospects of future SACs study, aiming to pave the way for their widespread application in industrial processes.