CO2 to Value-Added Chemicals: Synthesis and Performance of Mono- and Bimetallic Nickel–Cobalt Nanofiber Catalysts

Abstract

In an epoch dominated by escalating concerns over climate change and looming energy crises, the imperative to design highly efficient catalysts that can facilitate the sequestration and transformation of carbon dioxide (CO2) into beneficial chemicals is paramount. This research presents the successful synthesis of nanofiber catalysts, incorporating monometallic nickel (Ni) and cobalt (Co) and their bimetallic blend, NiCo, via a facile electrospinning technique, with precise control over the Ni/Co molar ratios. Application of an array of advanced analytical methods, including SEM, TGA–DSC, FTIR-ATR, XRD, Raman, XRF, and ICP-MS, validated the effective integration and homogeneous distribution of active Ni/Co catalysts within the nanofibers. The catalytic performance of these mono- and bimetallic Ni/Co nanofiber catalysts was systematically examined under ambient pressure conditions for CO2 hydrogenation reactions. The bimetallic NiCo nanofiber catalysts, specifically with a Ni/Co molar ratio of 1:2, and thermally treated at 1050 °C, demonstrated a high CO selectivity (98.5%) and a marked increase in CO2 conversion rate—up to 16.7 times that of monometallic Ni nanofiber catalyst and 10.8 times that of the monometallic Co nanofiber catalyst. This significant enhancement in catalytic performance is attributed to the improved accessibility of active sites, minimized particle size, and the strong Ni–Co–C interactions within these nanofiber structures. These nanofiber catalysts offer a unique model system that illuminates the fundamental aspects of supported catalysis and accentuates its crucial role in addressing pressing environmental challenges.

Harnessing the Synergy of Fe and Co with Carbon Nanofibers for Enhanced CO2 Hydrogenation Performance

“…Following the fabrication step, these precursor composite nanofibers were subjected to a series of heat treatments under an inert atmosphere. The temperatures selected for these treatments, specifically 450, 850, 1050, and 1250 °C, have been consistently applied, as documented in our prior research . The goal of these treatments was to convert the Fe/Co salts to their metallic states and concurrently convert PAN to CNFs.…”

“…On the other end of the spectrum, metal loadings below 5% resulted in subpar hydrogenation performance, rendering the catalysts impractical for real-world applications . Additionally, our previous studies have indicated that a molar ratio of 1/2 (Fe/Co) is optimal for bimetallic nanofiber catalysts, promoting an enhanced electronic structure conducive to catalytic activity . Therefore, through recipe optimization, the Fe content was established at 5.00% and the Co content at 10.55% in the monometallic nanofibers (Table ).…”

“…The temperatures selected for these treatments, specifically 450, 850, 1050, and 1250 °C, have been consistently applied, as documented in our prior research. 37 The goal of these treatments was to convert the Fe/Co salts to their metallic states and concurrently convert PAN to CNFs. Post-thermal treatment observations revealed an increase in sample brittleness, more pronounced in monometallic Fe or Co nanofibers compared to bimetallic FeCo nanofibers treated under identical conditions ( Figure 1 A–C).…”

“… 43 Additionally, our previous studies have indicated that a molar ratio of 1/2 (Fe/Co) is optimal for bimetallic nanofiber catalysts, promoting an enhanced electronic structure conducive to catalytic activity. 37 Therefore, through recipe optimization, the Fe content was established at 5.00% and the Co content at 10.55% in the monometallic nanofibers ( Table 1 ). To maintain identical metal loadings in the bimetallic nanofibers, the Fe and Co contents were set at 5.00 and 10.55%, respectively, adhering to a 1/2 Fe/Co molar ratio.…”

“…Notably, the monometallic Co nanofibers showcased a proliferation of nanofibrils, hinting at a potential formation of CNTs, as Co is a well-documented catalyst for CNT growth. 37,38 With further elevation of the calcination temperature to 1050 °C, there was a notable increase in the number of nanoparticles on the nanofiber surfaces (Figure 1J−L). Impressively, numerous nanoparticles with dimensions of less than 10 nm persisted on the bimetallic FeCo nanofiber surfaces (Figure 1L).…”