Water–Gas Shift Reaction on Metal Nanoclusters Encapsulated in Mesoporous Ceria Studied with Ambient-Pressure X‑ray Photoelectron Spectroscopy

Metal nanoclusters (Au, Pt, Pd, Cu) encapsulated in channels of mesoporous ceria (<i>mp-</i>CeO₂) were synthesized. The activation energies of water–gas shift (WGS) reaction performed at oxide–metal interfaces of metal nanoclusters encapsulated in <i>mp</i>-CeO₂ (M@<i>mp</i>-CeO₂) are lower than those of metal nanoclusters impregnated on ceria nanorods (M/rod-CeO₂). <i>In situ</i> studies using ambient-pressure XPS (AP-XPS) suggested that the surface chemistry of the internal concave surface of CeO₂ pores of M@<i>mp</i>-CeO₂ is different from that of external surfaces of CeO₂ of M/rod-CeO₂ under reaction conditions. AP-XPS identified the metallic state of the metal nanoclusters of these WGS catalysts (M@<i>mp</i>-CeO₂ and M/rod-CeO₂) under a WGS reaction condition. The lower activation energy of M@<i>mp</i>-CeO₂ in contrast to M/rod-CeO₂ is related to the different surface chemistry of the two types of CeO₂ under the same reaction condition

Carbon Dioxide Hydrogenation over a Metal-Free Carbon-Based Catalyst

The hydrogenation of CO₂ into useful chemicals provides an industrial-scale pathway for CO₂ recycling. The lack of effective thermochemical catalysts currently precludes this process, since it is challenging to identify structures that can simultaneously exhibit high activity and selectivity for this reaction. Here, we report, for the first time, the use of nitrogen-doped graphene quantum dots (NGQDs) as metal-free catalysts for CO₂ hydrogenation. The nitrogen dopants, located at the edge sites, play a key role in inducing thermocatalytic activity in carbon nanostructures. Furthermore, the thermocatalytic activity and selectivity of NGQDs are governed by the doped N configurations and their corresponding defect density. The increase of pydinic N concentration at the edge site of NGQDs leads to lower initial reaction temperature for CO₂ reduction and also higher CO₂ conversion and selectivity toward CH₄ over CO