Yolk-Shell Nanocapsule Catalysts as Nanoreactors with Various Shell Structures and Their Diffusion Effect on the CO2 Reforming of Methane

Investigation of Ni-Cu-acid multifunctional synergism in NiCu-phyllosilicate catalysts toward the 1,4-butynediol hydrogenation to 1,4-butanediol

We studied the Ni-Cu-acid multifunctional synergism in NiCu-phyllosilicate catalysts toward 1,4-butynediol hydrogenation to 1,4-butanediol by varying the reduction temperature, which can activate different bimetal and support interactions. Compared with a monometallic Ni phyllosilicate (phy), which only showed one type of metal species when reduced at ∼750 °C, there are three types of metal species for the bimetallic Ni-Cu-phyllosilicate derived catalysts, namely Cuphy, differentiated Ni, and Niphy. Thorough structure-activity/selectivity correlation investigations showed that, although the Ni9Cu1-P catalyst matrix can produce tiny amounts of differentiated Ni0 species under the induction of reduced Cu0 at R250 condition, it could not form Ni-Cu bimetallic interactions for the collaborative hydrogenation of 1,4-butynediol, and the product stays in the semi hydrogenated state. When the reduction temperature is raised to 500 °C, stable Ni-Cu alloy active sites exist, accompanied by the strong metal support interaction and metal acid effect derived from the intimate contact between the extracted metal sites and the surviving functional phyllosilicate support; these functionalities yield a supreme hydrogenation performance of the R500 sample with a 1,4-butanediol yield larger than 91.2%.

Molecular Diffusion in Nanoreactors' Pore Channel System: Measurement Techniques, Structural Regulation, and Catalytic Effects

Nanoreactors, as a new class of materials with highly enriched and ordered pore channel structures, can achieve special catalytic effects by precisely identifying and controlling the molecular diffusion behavior within the ordered pore channel system. Nanoreactors-driven molecular diffusion within the ordered pore channels can be highly dependent on the local microenvironment in the nanoreactors' pore channel system. Although the diffusion process of molecules within the ordered pore channels of nanoreactors is crucial for the regulation of catalytic behaviors, it has not yet been as clearly elucidated as it deserves to be in this study. In this review, fundamental theory and measurement techniques for molecular diffusion in the pore channel system of nanoreactors are presented, structural regulation strategies of pore channel parameters for controlling molecular diffusion are discussed, and the effects of molecular diffusion in the pore channel system on catalytic reactivity and selectivity are further analyzed. This article attempts to further develop the underlying theory of molecular diffusion within the theoretical framework of nanoreactor-driven catalysis, and the proposed perspectives may contribute to the rational design of advanced catalytic materials and the precise control of complex catalytic kinetics.

Nanoreactor Engineering Can Unlock New Possibilities for CO2 Tandem Catalytic Conversion to C-C Coupled Products

Climate change is becoming increasingly more pronounced every day while the amount of greenhouse gases in the atmosphere continues to rise. CO₂ reduction to valuable chemicals is an approach that has gathered substantial attention as a means to recycle these gases. Herein, some of the tandem catalysis approaches that can be used to achieve the transformation of CO₂ to C-C coupled products are explored, focusing especially on tandem catalytic schemes where there is a big opportunity to improve performance by designing effective catalytic nanoreactors. Recent reviews have highlighted the technical challenges and opportunities for advancing tandem catalysis, especially highlighting the need for elucidating structure-activity relationships and mechanisms of reaction through theoretical and in situ/operando characterization techniques. In this review, the focus is on nanoreactor synthesis strategies as a critical research direction, and discusses these in the context of two main tandem pathways (CO-mediated pathway and Methanol-mediated pathway) to C-C coupled products.

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.

Alloying Ni-Cu Nanoparticles Encapsulated in SiO2 Nanospheres for Synergistic Catalysts in CO2 Reforming with Methane Reaction

In this work, we studied CO2 reforming with the methane (CRM) reaction over Ni-Cu alloy nanoparticles encapsulated in SiO2 nanospheres, for which combinational functions of alloy effect, size effect, metal-support interaction, and confinement effect exhibited high performance, good sintering resistance, and trace carbon deposition in CRM. The appropriate Cu-addition catalysts 0.2Cu-Ni@SiO2 and 0.5Cu-Ni@SiO2 had smaller NiCu alloy nanoparticles and a stronger metal-support interaction, exhibiting a better performance than the excessive Cu-addition catalysts 1.5Cu-Ni@SiO2 and 3Cu-Ni@SiO2 having Cu clusters and a weaker metal-support interaction. The best synergy of alloy effect, size effect, confinement effect, and metal-support interaction in the 0.5Cu-Ni@SiO2 catalyst contributed to the highest rates of CH4 and CO2 in CRM reported so far. This work demonstrates the importance of appropriate Cu addition in Ni-Cu@SiO2 catalysts, and the synergy for perfectly resolving sintering and carbon deposition in CRM.

Spherical Ni Nanoparticles Supported by Nanosheet-Assembled Al2O3 for Dry Reforming of CH4: Elucidating the Induction Period and Its Excellent Resistance to Coking

The design and preparation of efficient coking-resistant catalysts for dry reforming of methane (DRM) is significant for industrial applications but a challenge for supported Ni catalysts. Nanosheet-assembled Al₂O₃ (NA-Al₂O₃) with hierarchical hollow microspheres was used to support Ni nanoparticles, which exhibits superior long-time stability and coking resistance for the DRM reaction from 700 to 800 °C without coke deposition. Active Ni species, exsolved from NiAl₂O₄ spinel, are aggregated into Ni nanoparticles and finally stabilize as spherical Ni nanoparticles of 18.0 nm due to the spatial confinement of hierarchical hollow microspheres of the NA-Al₂O₃ support after the DRM reaction for 60 h. The catalytic activity in the induction period of the Ni/(NA-Al₂O₃) catalyst increases because of the enhancement of the surface Ni⁰/(Ni⁰+Ni²⁺) ratio, that is, the increment of the amount of active Ni sites. The spherical Ni nanoparticles embedded in the NA-Al₂O₃ support, superior CO₂ adsorption ability, and more surface hydroxyl groups on the Ni/(NA-Al₂O₃) catalyst are the determining factors for its long-time stability and excellent anti-coking for the DRM reaction.