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•Alloyed NiCo catalysts outperform monometallic Ni and Co in activity and stability.•Ni is more selective than Co towards CH4 cracking and CO2 activation.•Co is more selective than Ni ...toward the Boudouard Reaction.
Nickel and cobalt-based catalysts are very promising candidates for the dry reforming of methane, but their role in regulating catalyst selectivity has thus far been overlooked. Here we report the significant impact that catalyst selectivity has on the performance of Ni and Co catalysts for the dry reforming of methane. The role of Ni and Co in defining catalyst selectivity was examined via in-depth investigations into the tendency of catalysts towards the Boudouard, methane cracking and reverse water gas shift side reactions. Decoupling the side reactions demonstrated that Co deposits have a high affinity for the removal of carbon species via oxidation, while Ni is more active towards CH4 decomposition. Thereby superior catalytic performance is accessed via a combination of the high activity of Ni towards CH4 with the stabilising effect and carbon-resistance of Co. Characterisation of the materials illustrated the formation of well-dispersed NiCo alloys on the FSP-alumina, with the resulting strong bimetallic interactions fuelling enhanced catalytic performance via suppression of catalyst selectivity of Co towards the Boudouard reaction and Ni towards methane cracking.
From nurturing living organisms to feeding billions of people, the transformation of atmospheric nitrogen to ammonia (NH
3
) is essential to sustain life on earth. In nature, bacteria and plants can ...produce ammonia from air and water at ambient conditions
via
nitrogen fixation processes. To follow this feat, we couple plasma-driven nitrogen oxides intermediary (NO
x
) generation and their electrocatalytic reduction to pave the way for scalable green ammonia at ambient conditions. We developed a non-thermal plasma bubble column reactor that brings together dual reactor configuration with multiple discharge schemes and bubble dynamic control to generate NO
x
intermediaries at low specific energy consumption of 3.8 kW h mol
−1
. The NO
x
intermediaries were converted to ammonia at a rate of 23.2 mg h
−1
(42.1 nmol cm
−2
s
−1
), using a scalable electrolyzer operating at a low cell voltage of 1.4 V, current densities of over 50 mA cm
−2
, and specific energy consumption of 0.51 kW h mol
−1
NH
3
.
Sustainable ammonia production using water and air through the coupling of plasma-driven intermediary NO
x
generation and their electrocatalytic conversion.
Silica particles were prepared by flame spray pyrolysis (FSP) as a support for nickel catalysts. The impact of precursor feed rate (3, 5 and 7 mL/min) during FSP on the silica characteristics and the ...ensuing effect on catalytic performance for the carbon dioxide, or dry, reforming of methane (DRM) was probed. Increasing the precursor feed rate: (i) progressively lowered the silica surface area from ≈340 m2/g to ≈240 m2/g; (ii) altered the silanol groups on the silica surface; and (iii) introduced residual carbon-based surface species to the sample at the highest feed rate. The variations in silica properties altered the (5 wt %) nickel deposit characteristics which in turn impacted on the DRM reaction. As the silica surface area increased, the nickel dispersion increased which improved catalyst performance. The residual carbon-based species also appeared to improve nickel dispersion, and in turn catalyst activity, although not to the same extent as the change in silica surface area. The findings illustrate both the importance of silica support characteristics on the catalytic performance of nickel for the DRM reaction and the capacity for using FSP to control these characteristics.
Improving the stability of cuprous oxide (Cu2O) is imperative to its practical applications in artificial photosynthesis. In this work, Cu2O nanowires are encapsulated by metal–organic frameworks ...(MOFs) of Cu3(BTC)2 (BTC=1,3,5‐benzene tricarboxylate) using a surfactant‐free method. Such MOFs not only suppress the water vapor‐induced corrosion of Cu2O but also facilitate charge separation and CO2 uptake, thus resulting in a nanocomposite representing 1.9 times improved activity and stability for selective photocatalytic CO2 reduction into CH4 under mild reaction conditions. Furthermore, direct transfer of photogenerated electrons from the conduction band of Cu2O to the LUMO level of non‐excited Cu3(BTC)2 has been evidenced by time‐resolved photoluminescence. This work proposes an effective strategy for CO2 conversion by a synergy of charge separation and CO2 adsorption, leading to the enhanced photocatalytic reaction when MOFs are integrated with metal oxide photocatalyst.
Cu2O nanowires are decorated with Cu3(BTC)2 by a surfactant‐free method. The Cu2O@Cu3(BTC)2 core–shell structure offers enlarged active surfaces and prolonged lifetime of separated electrons for CO2 reduction into CH4, exhibiting enhanced photocatalytic activity and stability compared to the bare Cu2O.
Sluggish reaction kinetics and the undesired side reactions (hydrogen evolution reaction and self‐reduction) are the main bottlenecks of electrochemical conversion reactions, such as the carbon ...dioxide and nitrate reduction reactions (CO2RR and NO3RR). To date, conventional strategies to overcome these challenges involve electronic structure modification and modulation of the charge‐transfer behavior. Nonetheless, key aspects of surface modification, focused on boosting the intrinsic activity of active sites on the catalyst surface, are yet to be fully understood. Engingeering of oxygen vacancies (OVs) can tune surface/bulk electronic structure and improve surface active sites of electrocatalysts. The continuous breakthroughs and significant progress in the last decade position engineering of OVs as a potential technique for advancing electrocatalysis. Motivated by this, the state‐of‐the‐art findings of the roles of OVs in both the CO2RR and the NO3RR are presented. The review starts with a description of approaches to constructing and techniques for characterizing OVs. This is followed by an overview of the mechanistic understanding of the CO2RR and a detailed discussion on the roles of OVs in the CO2RR. Then, insights into the NO3RR mechanism and the potential of OVs on NO3RR based on early findings are highlighted. Finally, the challenges in designing CO2RR/NO3RR electrocatalysts and perspectives in studying OV engineering are provided.
Boosting the intrinsic activity of active sites on oxide surfaces is a critical factor in promoting electrochemical conversion reactions. A special focus is placed on the structure–performance relationship of oxygen vacancies in carbon dioxide reduction reaction (CO2RR)/nitrate reduction reaction (NO3RR) electrocatalysts. This work examines the formation/characterization of defects for CO2RR, taking learnings, challenges, and future directions in designing defective oxides for the emerging field of NO3RR.
A novel, simple and controllable approach to designing NiO/Ni heterostructures supported on carbon for the hydrogen evolution reaction (HER) was utilized. By selectively oxidizing the Ni deposits, to ...differing degrees, the benefits of the NiO/Ni heterostructures were elucidated with the extent of Ni oxidation being a key factor in dictating performance.
A novel, simple and controllable approach to designing NiO/Ni heterostructures supported on carbon for the hydrogen evolution reaction (HER) was utilized.
Single‐atom catalysts (SACs) have been at the frontier of research field in catalysis owing to the maximized atomic utilization, unique structures and properties. The atomically dispersed and ...catalytically active metal atoms are necessarily anchored by surrounding atoms. As such, the structure and composition of anchoring sites significantly influence the catalytic performance of SACs even with the same metal element. Significant progress has been made to understand structure–activity relationships at an atomic level, but in‐depth understanding in precisely designing highly efficient SACs for the targeted reactions is still required. In this review, various anchoring sites in SACs are summarized and classified into five different types (doped heteroatoms, defect sites, surface atoms, metal sites, and cavity sites). Then, their impacts on catalytic performance are elucidated for electrochemical reactions based on their distance from the metal center (first coordination shell and beyond). Further, SACs anchored on two typical types of hosts, carbon‐ and metal‐based materials, are highlighted, and the effects of anchoring points on achieving the desirable atomic structure, catalytic performance, and reaction pathways are elaborated. At last, insights and outlook to the SAC field based on current achievements and challenges are presented.
Single‐atom catalysts (SACs) with isolated metal atoms stabilized on various supports by surrounding atoms have emerged as a new frontier. The atomic structure and composition of anchoring sites significantly influence the catalytic performance of SACs. An overview of the correlation between the property of anchoring points and catalytic performance to guide the design of SACs is provided.
The vast chemical and structural tunability of metal–organic frameworks (MOFs) are beginning to be harnessed as functional supports for catalytic nanoparticles spanning a range of applications. ...However, a lack of straightforward methods for producing nanoparticle‐encapsulated MOFs as efficient heterogeneous catalysts limits their usage. Herein, a mixed‐metal MOF, NiMg‐MOF‐74, is utilized as a template to disperse small Ni nanoclusters throughout the parent MOF. By exploiting the difference in NiO and MgO coordination bond strength, Ni2+ is selectively reduced to form highly dispersed Ni nanoclusters constrained by the parent MOF pore diameter, while Mg2+ remains coordinated in the framework. By varying the ratio of Ni to Mg in the parent MOF, accessible surface area and crystallinity can be tuned upon thermal treatment, influencing CO2 adsorption capacity and hydrogenation selectivity. The resulting Ni nanoclusters prove to be an active catalyst for CO2 methanation and are examined using extended X‐ray absorption fine structure and X‐ray photoelectron spectroscopy. By preserving a segment of the Mg2+‐containing MOF framework, the composite system retains a portion of its CO2 adsorption capacity while continuing to deliver catalytic activity. The approach is thus critical for designing materials that can bridge the gap between carbon capture and CO2 utilization.
The thermal treatment of mixed‐metal metal–organic frameworks (MOFs) is harnessed to bridge the gap between direct air capture and CO2 methanation with one material. Ni2+ is selectively reduced within the MOF to form highly dispersed Ni nanoclusters active for CO2 hydrogenation. Over 70% of the CO2 adsorption capacity is preserved for the best‐performing catalysts, highlighting the dual functionality of the nanoparticle‐MOF structure.
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•Unique SiO2/Ce0.7Zr0.3O2 structures synthesised by FSP for methane dry reforming.•Support composition and structure dictates properties of the silica/ceria-zirconia.•Coupling silica ...with ceria-zirconia enhances Ni-based catalyst performance.
Flame spray pyrolysis (FSP) was used to design silica/ceria-zirconia particles with assorted structures as Ni catalyst supports for the carbon dioxide reforming of methane. The FSP precursor feed was varied to produce either mixed-oxide or core-shell arrays. The structures exhibited diversity in their properties including surface area and oxygen storage capacity. NiO deposit size decreased with increasing ceria-zirconia content, from 14nm for the neat SiO2 to 5nm for the neat Ce0.7Zr0.3O2. Compared to the neat supports, the co-operative benefits of coupling the silica with the ceria-zirconia were clear. Introducing ceria-zirconia to the silica enabled the mixed supports to outperform the neat silica by supressing methane decomposition and promoting the dry reforming reaction. Introducing silica to the ceria-zirconia enabled the mixed supports to outperform the neat ceria-zirconia by decreasing susceptibility toward the reverse water gas shift reaction and preventing deactivation at 700°C, attributed to better support thermal stability.
Sluggish reaction kinetics and the undesired side reactions (hydrogen evolution reaction and self-reduction) are the main bottlenecks of electrochemical conversion reactions, such as the carbon ...dioxide and nitrate reduction reactions (CO
RR and NO
RR). To date, conventional strategies to overcome these challenges involve electronic structure modification and modulation of the charge-transfer behavior. Nonetheless, key aspects of surface modification, focused on boosting the intrinsic activity of active sites on the catalyst surface, are yet to be fully understood. Engingeering of oxygen vacancies (OVs) can tune surface/bulk electronic structure and improve surface active sites of electrocatalysts. The continuous breakthroughs and significant progress in the last decade position engineering of OVs as a potential technique for advancing electrocatalysis. Motivated by this, the state-of-the-art findings of the roles of OVs in both the CO
RR and the NO
RR are presented. The review starts with a description of approaches to constructing and techniques for characterizing OVs. This is followed by an overview of the mechanistic understanding of the CO
RR and a detailed discussion on the roles of OVs in the CO
RR. Then, insights into the NO
RR mechanism and the potential of OVs on NO
RR based on early findings are highlighted. Finally, the challenges in designing CO
RR/NO
RR electrocatalysts and perspectives in studying OV engineering are provided.
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