Revamping SiO₂ Spheres by Core–Shell Porosity Endowment to Construct a Mazelike Nanoreactor for Enhanced Catalysis in CO₂ Hydrogenation to Methanol

Abstract

Beyond the catalytic activity of nanocatalysts, the support with architectural design and explicit boundary could also promote the overall performance through improving the diffusion process, highlighting additional support for the morphology-dependent activity. To delineate this, herein, a novel mazelike-reactor framework, namely multi-voids mesoporous silica sphere (MVmSiO 2 ), is carved through a top-down approach by endowing core-shell porosity premade Stöber SiO 2 spheres. The precisely-engineered MVmSiO 2 with peripheral one-dimensional pores in the shell and interconnecting compartmented voids in the core region is simulated to prove combined hierarchical and structural superiority over its analogous counterparts. Supported with CuZn-based alloys, mazelike MVmSiO 2 nanoreactor experimentally demonstrated its expected workability in model gas-phase CO 2 hydrogenation reaction where enhanced CO 2 activity, good methanol yield, and more importantly, a prolonged stable performance are realized. While tuning the nanoreactor composition besides morphology optimization could further increase the catalytic performance, it is accentuated that the morphological architecture of support further boosts the reaction performance apart from comprehensive compositional optimization. In addition to the found morphological restraints and size-confinement effects imposed by MVmSiO 2 , active sites of catalysts are also investigated by exploring the size difference of the confined CuZn alloy nanoparticles in CO 2 hydrogenation employing both in-situ experimental characterizations and density functional theory calculations.

Single Solid Precursor-Derived Three-Dimensional Nanowire Networks of CuZn-Silicate for CO2 Hydrogenation to Methanol

“…As Cu is usually accountable for the high activity of the RWGS reaction, it is believed that the incorporation of ZnO into the catalyst enhanced the formation of *HCOO species and greatly improved the MeOH selectivity, leading to an overall higher specific MeOH yield with low CO production. Encouragingly, it has been discovered that the formate species adsorbed on a clean Cu(111) surface mainly appears as the ν s (OCO) peaks at ∼1351 and 1390 cm –1 , while the ν as (OCO) peak at ∼1590 cm –1 is more profound for formate species adsorbed on the Zn-decorated Cu(111) surface (our catalyst) . Moreover, the measured absorbance at 1590 cm –1 is in line with the previous DFT-calculated IR frequencies for *HCOO adsorbed on Cu–Zn surface alloys .…”

“…Encouragingly, it has been discovered that the formate species adsorbed on a clean Cu(111) surface mainly appears as the ν s (OCO) peaks at ∼1351 and 1390 cm –1 , while the ν as (OCO) peak at ∼1590 cm –1 is more profound for formate species adsorbed on the Zn-decorated Cu(111) surface (our catalyst) . Moreover, the measured absorbance at 1590 cm –1 is in line with the previous DFT-calculated IR frequencies for *HCOO adsorbed on Cu–Zn surface alloys . The dominance of intensified signals at 1590 cm –1 over 1351 and 1390 cm –1 advocates for the presence of a large amount of Cu–Zn surface alloys in our catalysts under the reaction conditions.…”

“…Therefore, it becomes a trade-off problem between the high single-pass CO 2 conversion and high MeOH yield. Moreover, the high long-term stability of our Si–Cu–Zn catalyst would favor the application, and in contrast, the catalytic activity of the commercial catalyst was found to drop significantly in 14 h of operation under identical conditions . In addition to catalyst performance and stability, the manufacturing cost is another consideration for more effective utilization of transition metals such as copper, whose price has increased four times over the past two decades.…”

“…Such a tremendous improvement is attributed to the synergistic effect between Cu and ZnO, particularly owing to the strong metal–support interaction (SMSI). ,,,, Other studies have demonstrated that ZnO may form a “graphite-like” overlayer on Cu nanoparticles. , On the other hand, ZnO might be partially reduced into ZnO x species that considerably alter the electronic properties at the Cu–ZnO interface since it can be slightly reducible under the reaction conditions. , Furthermore, it was claimed that Zn δ+ or Zn 0 may migrate into Cu due to the Kirkendall effect, forming Cu–Zn alloys. − It was proposed that the incorporation of Zn into Cu further strengthens the binding of intermediates . Specifically, the Cu–Zn surface alloy was proposed to be one of the active sites for CO 2 hydrogenation to methanol in both CuZn–Si and CuZnZr–Si catalysts . The postulation was further corroborated by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) modeling with regard to the adsorbed formate species on these Cu–Zn surface alloys .…”

From 1D Nanofibers to 3D Nanofibrous Aerogels: A Marvellous Evolution of Electrospun SiO2 Nanofibers for Emerging Applications

“…In fact, Stöber first invented a method in 1968 for synthesizing monodispersed zero-dimensional (0D) SiO 2 particles with sizes as small as about 50 nm [ 6 ]. Since then, researchers have carried out a series of work on this basis and made some progress in the fields of medicine, sensing, and catalysis [ 7 – 9 ]. However, these spherical SiO 2 nanoparticles are easy to agglomerate, easy to fall off from the substrates, and difficult to recycle, which lay thorny problems for their use.…”