Accelerated discovery of multi-elemental reverse water-gas shift catalysts using extrapolative machine learning approach.

Designing novel catalysts is key to solving many energy and environmental challenges. Despite the promise that data science approaches, including machine learning (ML), can accelerate the development of catalysts, truly novel catalysts have rarely been discovered through ML approaches because of one of its most common limitations and criticisms-the assumed inability to extrapolate and identify extraordinary materials. Herein, we demonstrate an extrapolative ML approach to develop new multi-elemental reverse water-gas shift catalysts. Using 45 catalysts as the initial data points and performing 44 cycles of the closed loop discovery system (ML prediction + experiment), we experimentally tested a total of 300 catalysts and identified more than 100 catalysts with superior activity compared to those of the previously reported high-performance catalysts. The composition of the optimal catalyst discovered was Pt(3)/Rb(1)-Ba(1)-Mo(0.6)-Nb(0.2)/TiO2. Notably, niobium (Nb) was not included in the original dataset, and the catalyst composition identified was not predictable even by human experts.

Bifunctionality of Re Supported on TiO2 in Driving Methanol Formation in Low-Temperature CO2 Hydrogenation.

Low temperature and high pressure are thermodynamically more favorable conditions to achieve high conversion and high methanol selectivity in CO2 hydrogenation. However, low-temperature activity is generally very poor due to the sluggish kinetics, and thus, designing highly selective catalysts active below 200 °C is a great challenge in CO2-to-methanol conversion. Recently, Re/TiO2 has been reported as a promising catalyst. We show that Re/TiO2 is indeed more active in continuous and high-pressure (56 and 331 bar) operations at 125-200 °C compared to an industrial Cu/ZnO/Al2O3 catalyst, which suffers from the formation of methyl formate and its decomposition to carbon monoxide. At lower temperatures, precise understanding and control over the active surface intermediates are crucial to boosting conversion kinetics. This work aims at elucidating the nature of active sites and active species by means of in situ/operando X-ray absorption spectroscopy, Raman spectroscopy, ambient-pressure X-ray photoelectron spectroscopy (AP-XPS), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Transient operando DRIFTS studies uncover the activation of CO2 to form active formate intermediates leading to methanol formation and also active rhenium carbonyl intermediates leading to methane over cationic Re single atoms characterized by rhenium tricarbonyl complexes. The transient techniques enable us to differentiate the active species from the spectator one on TiO2 support, such as less reactive formate originating from spillover and methoxy from methanol adsorption. The AP-XPS supports the fact that metallic Re species act as H2 activators, leading to H-spillover and importantly to hydrogenation of the active formate intermediate present over cationic Re species. The origin of the unique reactivity of Re/TiO2 was suggested as the coexistence of cationic highly dispersed Re including single atoms, driving the formation of monodentate formate, and metallic Re clusters in the vicinity, activating the hydrogenation of the formate to methanol.

The reducibility and oxidation states of oxide-supported rhenium: experimental and theoretical investigations.

The activity and stability of supported metal catalysts, which exhibit high efficiency and activity, are significantly influenced by the interactions between the metal and the support, that is, metal-support interactions (MSIs). Here, we report an investigation of the MSIs between supported rhenium (Re) and oxide supports such as TiO2, SiO2, Al2O3, MgO, V2O5, and ZrO2 using experimental and computational approaches. The reducibility of the Re species was found to strongly depend on the oxide support. Experimental studies including temperature-programmed reduction by H2 as well as Re L3- and L1-edge X-ray absorption near edge structure (XANES) analysis revealed that the valency of the Re species started to decrease upon H2 reduction in the 200-400 °C range, except for Re on MgO, where the shift occurred at temperatures above 500 °C. The dependence of the Re L3- and L1-edge XANES spectra of the oxide-supported Re catalysts on the size of Re was also examined.

Selective Transformations of Triglycerides into Fatty Amines, Amides, and Nitriles by using Heterogeneous Catalysis.

The use of triglycerides as an important class of biomass is an effective strategy to realize a more sustainable society. Herein, three heterogeneous catalytic methods are reported for the selective one-pot transformation of triglycerides into value-added chemicals: i) the reductive amination of triglycerides into fatty amines with aqueous NH3 under H2 promoted by ZrO2 -supported Pt clusters; ii) the amidation of triglycerides under gaseous NH3 catalyzed by high-silica H-beta (Hß) zeolite at 180 °C; iii) the Hß-promoted synthesis of nitriles from triglycerides and gaseous NH3 at 220 °C. These methods are widely applicable to the transformation of various triglycerides (C4 -C18 skeletons) into the corresponding amines, amides, and nitriles.