Probing the enhanced catalytic activity of carbon nanotube supported Ni-LaOx hybrids for the CO2 reduction reaction

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.

Streamlining the synthesis of amides using Nickel-based nanocatalysts

The synthesis of amides is a key technology for the preparation of fine and bulk chemicals in industry, as well as the manufacture of a plethora of daily life products. Furthermore, it constitutes a central bond-forming methodology for organic synthesis and provides the basis for the preparation of numerous biomolecules. Here, we present a robust methodology for amide synthesis compared to traditional amidation reactions: the reductive amidation of esters with nitro compounds under additives-free conditions. In the presence of a specific heterogeneous nickel-based catalyst a wide range of amides bearing different functional groups can be selectively prepared in a more step-economy way compared to previous syntheses. The potential value of this protocol is highlighted by the synthesis of drugs, as well as late-stage modifications of bioactive compounds. Based on control experiments, material characterizations, and DFT computations, we suggest metallic nickel and low-valent Ti-species to be crucial factors that makes this direct amide synthesis possible.

Engineering the Quaternary Hydrotalcite-Derived Ce-Promoted Ni-Based Catalysts for Enhanced Low-Temperature CO2 Hydrogenation into Methane

Ce-promoted NiMgAl mixed-oxide (NiCex-C, x = 0, 1, 5, 10) catalysts were prepared from the quaternary hydrotalcite precursors for CO₂ hydrogenation to methane. By engineering the Ce contents, NiCe5-C showed its prior catalytic performance in low-temperature CO₂ hydrogenation, being about three times higher than that of the Ce-free NiCe0-C catalyst (turnover frequency of NiCe5-C and NiCe0-C: 11.9 h^-1 vs. 3.9 h^-1 @ 225 °C). With extensive characterization, it was found that Ce dopants promoted the reduction of NiO by adjusting the interaction between Ni and Mg(Ce)AlOx support. The highest ratio of surface Ni⁰/(Ni²⁺ + Ni⁰) was obtained over NiCe5-C. Meanwhile, the surface basicity was tailored with Ce dopants. The strongest medium-strength basicity and highest capacity of CO₂ adsorption was achieved on NiCe5-C with 5 wt.% Ce content. The TOF tests indicated a good correlation with medium-strength basicity over the NiCex-C samples. The results showed that the high medium-strength and Ce-promoted surface Ni⁰ species endows the enhanced low-temperature catalytic performance in CO₂ hydrogenation to methane.

Ambient Hydrogenation and Deuteration of Alkenes Using a Nanostructured Ni-Core-Shell Catalyst

A general protocol for the selective hydrogenation and deuteration of a variety of alkenes is presented. Key to success for these reactions is the use of a specific nickel-graphitic shell-based core-shell-structured catalyst, which is conveniently prepared by impregnation and subsequent calcination of nickel nitrate on carbon at 450 °C under argon. Applying this nanostructured catalyst, both terminal and internal alkenes, which are of industrial and commercial importance, were selectively hydrogenated and deuterated at ambient conditions (room temperature, using 1 bar hydrogen or 1 bar deuterium), giving access to the corresponding alkanes and deuterium-labeled alkanes in good to excellent yields. The synthetic utility and practicability of this Ni-based hydrogenation protocol is demonstrated by gram-scale reactions as well as efficient catalyst recycling experiments.

The role of surface properties in CO2 methanation over carbon-supported Ni catalysts and their promotion by Fe

CO₂ methanation over activated carbon-supported Ni catalysts with enhanced surface chemistry properties and their improved performance by Fe promotion.

Industrial carbon dioxide capture and utilization: state of the art and future challenges

This review covers the sustainable development of advanced improvements in CO₂ capture and utilization.

Palladium Supported on Calcium Decorated Carbon Nanotube Hybrids for Chemoselective Hydrogenation of Cinnamaldehyde

The chemoselective hydrogenation of cinnamaldehyde (CAL) to the corresponding hydrocinamaldehyde (HCAL) is a type of important reactions in fine chemistry, which is critically dependent on the rational design the chemical structure of active metal. In this work, calcium promoted palladium on CNT hybrid (Ca-Pd@CNT) with monolithic structure was synthesized through one-pot alginate gel process. The catalytic performance results showed that moderate Ca promotion catalyst (Ca-Pd@CNTHCl-2h) present a superior CAL hydrogenation activity with CAL conversion of 99.9% and HCAL selectivity of 86.4% even at the lager Pd nanoparticle size (c.a. 5 nm). The characterization results show that the electron transfer between the additive Ca promoter and Pd nanoparticles (NPs) could modify the electron structure of Pd species and induce the formation of the partial positively charged Pdδ+ species on the Pd NPs surface in the Ca-Pd@CNTHCl-2h catalyst resulting to the satisfactory catalytic performance. Furthermore, the one-pot gel synthesis methodology for microscopic carbon supported catalyst could also endows its great potential industry application in heterogeneous catalysis with easily handling during the transportation and reaction, and attributed to reducing the overall pressure drop across in the fix-bed reactor.

Intentional construction of high-performance SnO2 catalysts with a 3D porous structure for electrochemical reduction of CO2

Herein, SnO₂-NC (SnO₂-nanocube) and SnO₂-NF (SnO₂-nanoflake) electro-catalysts featuring a large specific surface area and 3D porous structure were successfully constructed via acid etching and sulfurization-desulphurization methods, respectively. As catalysts for the electrochemical reduction of CO₂, the faradaic efficiency (F_HCOO^-+CO = 82.4%, 91.5%, respectively) and partial current density (j_HCOO^-+CO = 10.7 and 11.5 mA cm^-2, respectively) of SnO₂-NCs and SnO₂-NFs were enhanced in comparison with SnO₂-NPs (SnO₂-nanoparticles, F_HCOO^-+CO = 63.4%, j_HCOO^-+CO = 5.7 mA cm^-2) at -1.0 V vs. RHE. The enhanced catalytic activity is attributed to their uniform 3D porous structure, high specific surface area and excellent wettability. Additionally, the morphology of SnO₂-NCs and SnO₂-NFs was largely preserved after electrolyzing for 12 h (after 12 h of electrolysis), indicating the effective buffering effect of the 3D structure in electrolysis. Naturally, the current density and faradaic efficiency of the SnO₂-NC and SnO₂-NF catalysts remained nearly unchanged after long-term stability measurements, revealing great stability.

A new and different insight into the promotion mechanisms of Ga for the hydrogenation of carbon dioxide to methanol over a Ga-doped Ni(211) bimetallic catalyst

The hydrogenation of CO₂ to CH₃OH is one of the most promising technologies for the utilization of captured CO₂ in the future. Nano Ni-Ga bimetallic catalysts have been proven to be excellent catalysts in the hydrogenation of CO₂ to CH₃OH. To investigate the promotion mechanisms of Ga for the hydrogenation of CO₂ to CH₃OH over Ga-doped Ni catalysts and the wide application of these promotion mechanisms in other catalysts and reactions, herein, density functional theory (DFT) was employed. The reaction mechanisms and the properties of Ni(211) and Ga-Ni(211) surfaces were comparatively studied. The results show that the Ni sites on both the Ni(211) and the Ga-Ni(211) surfaces are active sites, and the most stable structures of the intermediates are similar. Moreover, the Ga-Ni(211) surface is more favorable for the hydrogenation of CO₂, whereas Ni(211) is more favorable for the dissociation of CO₂. The activation barrier of the rate-limiting step in the CH₃OH formation pathway on Ni(211) is 0.54 eV higher than that on Ga-Ni(211). According to the analyses of the projected density of states (PDOS) and Hirshfeld charge transfer, the addition of Ga atoms demonstrates the reactivity of the Ga-doped Ni(211) surfaces. Most importantly, the replacement of some secondary active sites of Ni atoms with the non-active Ga atoms may lower the activities of the secondary active sites and strengthen the activities of the active sites at the step edge. These results provide a new perspective for the reaction mechanism of the hydrogenation of CO₂ to CH₃OH over the state-of-the-art Ga-doped catalysts.

Regulation of Ni-CNT Interaction on Mn-Promoted Nickel Nanocatalysts Supported on Oxygenated CNTs for CO2 Selective Hydrogenation

Mn-promoted Ni nanoparticles (NPs) supported on oxygen-functionalized carbon nanotubes (CNTs) were synthesized for CO₂ hydrogenation to methane. This novel metal-carbon catalytic system was characterized by both experimental and computational studies. An anomalous metal-support interaction mode (i.e., a higher temperature would lead to a weakened Ni-CNT interaction) was observed. Deep investigation confirmed that surface oxygen groups (SOGs) on CNTs played a key role in tuning the Ni-CNT interaction. We proposed that high calcination temperature would firstly lead to the decomposition of SOGs (>400 °C), then causing a loss of anchoring sites and the anchoring effect of SOGs on Ni NPs, thus cutting off the connection between interfacial Ni atoms and CNT body, resulting in the migration and coalescence of fine flat Ni NPs into larger sphere ones at 550 °C (geometric effect). Density functional theory calculation study clarified that this kind of anchoring effect stemmed from the formation of covalent bonding between the interfacial Ni atom and C or O elements of SOGs, causing the electrons to be transferred from Ni atoms to CNT support because of the intrinsic electronegativity of -COOH (electronic effect). Besides, Mn promotion notably boosts the activity compared with unpromoted catalysts, which was irrelevant to the size effect, but enhanced CO₂ adsorption and conversion according to the result of CO₂-temperature programmed desorption and transient response experiment. The optimized NiMn350 catalyst endowed with Mn promotion and robust Ni-CNT interaction showed both high activity and sintering resistance for more than 140 h. Our findings paved the way to reasonably design the metal-carbon catalyst with both high activity and stability.