Hollow carbon-based materials for electrocatalytic and thermocatalytic CO2 conversion

Electrocatalytic and thermocatalytic CO2 conversions provide promising routes to realize global carbon neutrality, and the development of corresponding advanced catalysts is important but challenging. Hollow-structured carbon (HSC) materials with striking features, including unique cavity structure, good permeability, large surface area, and readily functionalizable surface, are flexible platforms for designing high-performance catalysts. In this review, the topics range from the accurate design of HSC materials to specific electrocatalytic and thermocatalytic CO2 conversion applications, aiming to address the drawbacks of conventional catalysts, such as sluggish reaction kinetics, inadequate selectivity, and poor stability. Firstly, the synthetic methods of HSC, including the hard template route, soft template approach, and self-template strategy are summarized, with an evaluation of their characteristics and applicability. Subsequently, the functionalization strategies (nonmetal doping, metal single-atom anchoring, and metal nanoparticle modification) for HSC are comprehensively discussed. Lastly, the recent achievements of intriguing HSC-based materials in electrocatalytic and thermocatalytic CO2 conversion applications are presented, with a particular focus on revealing the relationship between catalyst structure and activity. We anticipate that the review can provide some ideas for designing highly active and durable catalytic systems for CO2 valorization and beyond.

Impact of preparation method on nickel speciation and methane dry reforming performance of Ni/SiO2 catalysts

The methane dry reforming reaction can simultaneously convert two greenhouse gases (CH₄ and CO₂), which has significantly environmental and economic benefits. Nickel-based catalysts have been widely used in methane dry reforming in past decade due to their low cost and high activity. However, the sintering and coke deposition of catalysts severely limit their industrial applications. In this paper, three Ni/SiO₂ catalysts prepared by different methods were systematically studied, and the samples obtained by the ammonia evaporation method exhibited excellent catalytic performance. The characterization results such as H₂-TPR, XPS and TEM confirmed that the excellent performance was mainly attributed to the catalyst with smaller Ni particles, stronger metal-support interactions, and abundant Ni-O-Si units on the catalyst surface. The anti-sintering/-coking properties of the catalyst were significantly improved. However, the Ni/SiO₂-IM catalyst prepared by impregnation method had uneven distribution of nickel species and large particles, and weak metal-support interactions, showing poor catalytic performance in methane dry reforming. Since the nickel species were encapsulated by the SiO₄ tetrahedral network, the Ni/SiO₂-SG catalyst prepared by sol-gel method could not expose more effective active sites even if the nickel species were uniformly dispersed, resulting in poor dry reforming performance. This study provides guidance for the preparation of novel anti-sintering/-coking nickel-based catalysts.

Highly Dispersed NixGay Catalyst and La2O3 Promoter Supported by LDO Nanosheets for Dry Reforming of Methane: Synergetic Catalysis by Ni, Ga, and La2O3

A highly active and stable Ni-based catalyst is the focal point for research on dry reforming of methane (DRM). Here, NixGay/La2O3-LDO catalysts composed of highly dispersed NixGay and La2O3 nanoparticles supported by the MgO/Al2O3 layered double oxide (LDO) nanosheets were synthesized by chemical methods. According to transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), CO2-TPD, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and thermal gravitational analysis (TGA), a synergistic reaction mechanism was proposed to explain the superior performance of the Ni0.8Ga0.2/La2O3-LDO catalyst. The NixGay alloy catalyst provides an effective way to balance the speed of CH4 cracking and CO2 disassociation, and the La2O3 promoter enriched the CO2 and ensured the generation of active O in time. They worked together to inhibit carbon accumulation and significantly improve the catalyst's activity and stability.

Silica-confined Ru highly dispersed on ZrO2 with enhanced activity and thermal stability in dichloroethane combustion

An efficient strategy (spontaneous deposition to enhance noble metal dispersity and core-shell confinement to inhibit noble metal sintering) is presented to synthesize highly active and thermally stable Ru/ZrO2@SiO2 catalysts for dichloroethane combustion.

Smart Designs of Anti-Coking and Anti-Sintering Ni-Based Catalysts for Dry Reforming of Methane: A Recent Review

Dry reforming of methane (DRM) reaction has drawn much interest due to the reduction of greenhouse gases and production of syngas. Coking and sintering have hindered the large-scale operations of Ni-based catalysts in DRM reactions at high temperatures. Smart designs of Ni-based catalysts are comprehensively summarized in fourth aspects: surface regulation, oxygen defects, interfacial engineering, and structural optimization. In each part, details of the designs and anti-deactivation mechanisms are elucidated, followed by a summary of the main points and the recommended strategies to improve the catalytic performance, energy efficiency, and utilization rate.

Bimetallic Metal-Organic Framework-Derived Hybrid Nanostructures as High-Performance Catalysts for Methane Dry Reforming

Syngas, consisting of equimolar CO and H₂, is an important feedstock for large-scale production of a wide range of commodity chemicals including aldehyde, methanol, ammonia, and other oxygenated chemicals. Dry reforming of methane (DRM), proceeding by reacting greenhouse gases, CO₂ and CH₄, at high temperatures in the presence of a metal catalyst, is considered one of the most environmentally friendly routes for syngas production. Nevertheless, nonprecious metal-based catalysts, which can operate at relatively low temperatures for high product yields and selectivities, are required to drive the DRM process for industrial applications effectively. Here, we developed NiCo@C nanocomposites from a corresponding NiCo-based bimetallic metal-organic framework (MOF) to serve as high-performance catalysts for the DRM process, achieving high turnover frequencies (TOF) at low temperatures (>5.7 s^-1 at 600 °C) and high product selectivities (H₂/CO = 0.9 at 700 °C). The incorporation of Co in Ni catalysts improves the operation stability and light-off stability. The present development for MOF-derived nanocomposites opens a new horizon for design of DRM catalysts.

CH4 conversion over Ni/HZSM-5 catalyst in the absence of oxygen: decomposition or dehydroaromatization?

The different chemical states and locations of Ni species in HZSM-5 result in different directions of CH₄ reaction. Supported Ni clusters caused complete CH₄ decomposition, while Ni-exchanged sites anchored at Brønsted acid sites, can appropriately activate CH₄ into CH_x species which are important precursors to produce aromatics. This study suggests a catalyst construction strategy for selective conversion of CH₄ towards value-added chemicals by placing active metal at specific sites.

Dendritic silica with carbon dots and gold nanoclusters for dual nanozymes

dSCS-Au NPs were established for dual nanozymes with dendritic silica spheres containing C-dots and Au NCs.