Understanding Structure–Property Relationships of MoO₃-Promoted Rh Catalysts for Syngas Conversion to Alcohols

Abstract

Rh-based catalysts have shown promise for the direct conversion of syngas to higher oxygenates. Although improvements in higher oxygenate yield have been achieved by combining Rh with metal oxide promoters, details of the structure of the promoted catalyst and the role of the promoter in enhancing catalytic performance are not well understood. In this work, we show that MoO 3 -promoted Rh nanoparticles form a novel catalyst structure in which Mo substitutes into the Rh surface, leading to both a 66-fold increase in turnover frequency and an enhancement in oxygenate yield. By applying a combination of atomically controlled synthesis, in situ characterization, and theoretical calculations, we gain an understanding of the promoter-Rh interactions that govern catalytic performance for MoO 3 -promoted Rh. We use atomic layer deposition to modify Rh nanoparticles with monolayer-precise amounts of MoO 3 , with a high degree of control over the structure of the catalyst. Through in situ X-ray absorption spectroscopy, we find that the atomic structure of the catalytic surface under reaction conditions consists of Mo−OH species substituted into the surface of the Rh nanoparticles. Using density functional theory calculations, we identify two roles of MoO 3 : first, the presence of Mo−OH in the catalyst surface enhances CO dissociation and also stabilizes a methanol synthesis pathway not present in the unpromoted catalyst; and second, hydrogen spillover from Mo−OH sites to adsorbed species on the Rh surface enhances hydrogenation rates of reaction intermediates.

Scalable neutral H2O2 electrosynthesis by platinum diphosphide nanocrystals by regulating oxygen reduction reaction pathways

“…Ultrathin metal oxides by ALD have been applied to encapsulate the supported nanoparticles and improve the size stability of nanoparticle catalysts 35,36 . In order to minimize additional electrocatalytic effects from ALD overcoating layer, we chose the relatively inert Al 2 O 3 rather than the typical transition metal oxide promotors (e.g., Co 3 O 4 37 , MnO 38 , Fe 2 O 3 39 , and MoO 3 40 ). ALD of a thin Al 2 O 3 layer was carried out to stabilize the ultrasmall PtP 2 NCs on a commercial carbon support by alternately exposing the sample to cycles of trimethylaluminum (TMA) and water at 175°C (Fig.…”

Incorporating MoO3 Patches into a Ni Oxyhydroxide Nanosheet Boosts the Electrocatalytic Oxygen Evolution Reaction

“…As shown in Figure d, the absorption edges of the Mo K-edge XANES spectra for MoO 2 , MoO 3 , and NiMoNS locate at higher energies than that of Mo-foil. This is understandable, considering that the Mo in MoO 2 , MoO 3 , and NiMoNS are in oxidation states. − A pre-peak at 19 995 eV appears on the Mo K-edge XANES spectrum for MoO 3 , and is caused by the mixing of the 2p orbital of O atom with the 5p and 4d orbitals of Mo atom in MoO 3 . − The pre-peak at 19 995 eV is not observed for MoO 2 . On the Mo K-edge XANES spectrum of NiMoNS, the pre-peak at 19 995 eV is present but becomes smaller than that of MoO 3 , implying that parts of Mo 6+ are reduced to Mo 5+ on NiMoNS. − In EXAFS spectra (Figure e), the peaks of NiMoNS locate between MoO 2 and MoO 3 .…”

Designing Nanoparticles and Nanoalloys for Gas-Phase Catalysis with Controlled Surface Reactivity Using Colloidal Synthesis and Atomic Layer Deposition

“…Within the framework of hydrogenation reactions, recent applications of ALD have focused on the study of promotional elements without introducing significant changes in the catalyst's morphology. Asundi et al [296] performed a fundamental study of MoO 3 promotion of Rh/SiO 2 catalysts for the selective conversion of syngas to alcohols. MoO 3 /Rh/SiO 2 exhibited a~66-fold increase in TOF values compared to unpromoted catalysts and MeOH selectivities up to 36%.…”