Optimized Microwave-Based Synthesis of Thermally Stable Inverse Catalytic Core–shell Motifs for CO₂ Hydrogenation

Abstract

The rational synthesis of Cu@TiO2 core@shell nanowire (NW) structures was thoroughly explored using a microwave-assisted method through the tuning of experimental parameters such as but not limited to (i) controlled variation in molar ratios, (ii) the effect of discrete Ti precursors, (iii) the method of addition of the precursors themselves, and (iv) time of irradiation. Uniform coatings were obtained using Cu/Ti molar ratios of 1:2, 1:1, 2:1, and 4:1, respectively. It should be noted that although relative molar precursor concentrations primarily determined the magnitude of the resulting shell size, the dependence was nonlinear. Moreover, additionally important reaction parameters, such as precursor identity, the means of addition of precursors, and the reaction time, were individually explored with the objective of creating a series of optimized reaction conditions. As compared with Cu NWs alone, it is evident that both of the Cu@TiO2 core–shell NW samples, regardless of pretreatment conditions, evinced much better catalytic performance, up to as much as 20 times greater activity as compared with standard Cu NWs. These results imply the significance of the Cu/TiO2 interface in terms of promoting CO2 hydrogenation, because TiO2 alone is known to be inert for this reaction. Furthermore, it is additionally notable that the N2 annealing pretreatment is crucial in terms of preserving the overall Cu@TiO2 core@shell structure. We also systematically analyzed and tracked the structural and chemical evolution of our catalysts before and after the CO2 reduction experiments. Indeed, we discovered that the core@shell wire motif was essentially maintained and conserved after this high-temperature reaction process, thereby accentuating the thermal stability and physical robustness of our as-prepared hierarchical motifs.

Exploring Strategies toward Synthetic Precision Control within Core–Shell Nanowires

“…In effect, the synthesis of Cu@TiO 2 core@shell catalytic NW structures was thoroughly investigated using a microwave-assisted method through the tuning of experimental parameters such as (i) the controlled variation in molar ratios, (ii) the use of different Ti precursors, (iii) the method of addition of the precursors themselves, and (iv) the irradiation time. Homogeneous coatings were generated using Cu:Ti molar ratios of 1:2, 1:1, 2:1, and 4:1, respectively (Figure A).…”

“…(D) Normalized CO 2 hydrogenation activity [in μmol/(g Cu s)] for Cu@TiO 2 samples in the absence of any N 2 annealing along with data for the corresponding Cu NW controls. Reproduced with permission from ref . Copyright 2020 American Chemical Society.…”

“…By contrast, precursor type, method of shell precursor addition, and irradiation time were more significant determinants of shell uniformity in the case of microwave-based techniques. The inherent flexibility and demonstrated efficacy of this synthetic toolkit is particularly important, considering that well-defined core–shell materials have found broad use in a wide variety of key applications, spanning energy, biomedicine, and sensing, in addition to electrochemical, thermochemical, and photochemical catalysis. ,,, …”

“…Moreover, the idea of being able to rationally design nanomaterials with tunable properties (and hence structure–property correlations) remains an appealing synthetic objective in nanochemistry. In this context, an ongoing objective within our group has been to generate effective, sustainable protocols with the goal of producing more complicated multiatom, nanoscale architectures and heterojunctions, which can be similarly probed and defined at the molecular level using a suite of advanced characterization tools. − Specifically, the goal of synthesizing heterostructures and variants thereof is to combine the favorable attributes of individual, distinctive atoms into an integrated, multifunctional unit with often unique and potentially superior properties. , …”

A Mini Review on Yolk-Shell Structured Nanocatalysts

“…Core-shell nanomaterials have received enormous attention owing to their unique structure related properties and the broad variety of ways in which they can be applied in energy storage (Xie et al, 2015;Lu et al, 2019), sensing (Gong et al, 2019), cancer therapy (Wang et al, 2018b;He et al, 2020), and in particular, catalysis (Gawande et al, 2015;Das et al, 2020;Salvatore et al, 2020). By tuning the intrinsic properties of the core or shell, a variety of nanocatalysts, with active centers that are properly shielded by permeable shells, are ready to be designed and fabricated (Murugesan et al, 2020;Wang et al, 2020).…”