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Catalytic reduction of CO2 by ethane creates an opportunity to use the shale gas and CO2 as the raw materials to produce syngas via dry reforming. In the present work, Pt-Ni bimetallic catalysts were investigated on reducible (CeO2, TiO2) and irreducible (γ-Al2O3, SiO2) oxides. The results showed that catalysts supported on reducible oxides, especially CeO2, were more active than those supported on irreducible oxides. Pulse and flow reactor studies and infrared spectroscopy experiments revealed a bi-functional Mars-Van Krevelen redox mechanism on PtNi/CeO2 and a mono-functional Langmuir-Hinshelwood mechanism on PtNi/SiO2, providing insights into the effects of reducibility of oxide supports on the reaction kinetics. Additionally, compared with the non-reducible SiO2, in situ X-ray diffraction (XRD) and pulse reactor analysis revealed that CO2 could be effectively activated on the reducible CeO2 and formed surface oxygen species to promote ethane dissociation into active carbon species. Thermogravimetric analysis (TGA), Transmission electron microscopy (TEM) and Raman spectroscopy showed that cokes formed on PtNi/CeO2 were primarily disordered/amorphous carbon species that could be easily removed during reforming.

Sub-nanometer Rh clusters derived from Rh-doped SrTiO3, demonstrated by in-situ X-ray Diffraction (XRD) and X-ray Absorption Fine Structure (XAFS) measurements, are applied as highly active catalysts for CO2 reduction. Compared to the supported Rh/SrTiO3, the catalyst synthesized by a doping-segregation method exhibits a higher space-time yield (STY) to CO with a selectivity of 95% for CO2 reduction by hydrogen; it also shows a higher activity with a larger turnover frequency (TOF) for CO2 reduction by ethane. According to the in-situ diffuse reflectance infrared Fourier transformed spectroscopy (DRIFTS) experiments, the higher CO selectivity for CO2 hydrogenation is attributed to the lower CO binding strength resulted by the strong interactions (e.g., charge transfer) between Rh atoms and the oxide support with surface defects. The superior activity is suggested to be originated from the cooperative effect between the highly dispersed sub-nanometer Rh clusters for efficient dissociation of H2/C2H6 and the reconstructed SrTiO3 with oxygen vacancies for preferential adsorption/activation of CO2. The doping-segregation method provides a unique opportunity to tune the size of active metal clusters and the physicochemical properties of the oxide support, offering the potential for applications in a variety of chemical reactions.

Dry reforming of methane provides opportunities of using CH4 and CO2 to produce syngas. The PtCo/CeO2 bimetallic catalyst shows higher activity and H2/CO ratio than the corresponding monometallic catalysts, mainly attributed to the synergistic effect of Pt-Co. Structural feature of the PtCo/CeO2 catalyst was revealed by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of adsorbed CO and in situ techniques like X-ray diffraction (XRD), X-ray adsorption fine structure (XAFS) and ambient-pressure X-ray photoelectron spectroscopy (AP-XPS). Pt-Co alloy and separated Co particles co-existed in the bimetallic catalyst, whereas the former was determined as the dominant active structure with a Pt-Co-mixed-surface termination. During reaction, Pt and Co in the alloy structure nearly maintained their metallic state with slight oxygen decoration, yielding oxygen-metal site-pairs (O*-*). Combined kinetic investigations and DFT calculations reveal that the O*-modified catalytic surface of PtCo/CeO2 promotes C H bond activation with higher entropy contribution (less constraints) to compensate its higher activation barrier. Thermogravimetric analysis (TGA), transmission electron microscope (TEM) and Raman spectroscopy show that the PtCo/CeO2 catalyst is resistant to coke formation as effectively as Pt/CeO2 and can be easily regenerated by a mild CO2 treatment.

Conversion of methanol and dimethyl ether (DME) to high-octane gasoline catalyzed by beta zeolite (BEA) provides an opportunity for the production of high-quality fuels from renewable carbon sources (e.g., gasified biomass). Recent research demonstrated that a Cu-modified BEA zeolite catalyst (Cu/BEA) offered advantages over the unmodified BEA catalyst due to multifunctional Cu species that enabled incorporation of co-fed H2, reactivation of light alkanes, and reduction of products from the aromatic hydrocarbon pool. The shift in hydrocarbon pool chemistry has the potential to influence the identity and relative composition of surface carbon species that are often linked to deactivation. A detailed understanding of these carbon species is important to develop an effective and efficient regeneration procedure that can enable the transition from fundamental catalyst development to commercial application. Here, we applied complementary ex situ and in situ characterization techniques to compare the structures of surface carbon species on post-reaction Cu/BEA and unmodified BEA catalysts. Both catalysts contained acyclic and aromatic hydrocarbons along with graphitic carbon species. However, the post-reaction Cu/BEA catalyst had a lower polycyclic aromatic content, and further, the graphitic species were more hydrogenated and defective. It was also found that the presence of Cu promoted carbon removal at lower temperatures than for unmodified BEA through activation of O2 by Cu oxide during thermal oxidation. The fundamental insight into the composition of surface carbon species enabled the design of an effective and efficient regeneration strategy for the DME homologation reaction over Cu/BEA, resulting in full recovery of the catalyst activity.