Porous Silicon Carbide (SiC): A Chance for Improving Catalysts or Just Another Active-Phase Carrier?

Abstract

There is an obvious gap between efforts dedicated to the control of chemicophysical and morphological properties of catalyst active phases and the attention paid to the search of new materials to be employed as functional carriers in the upgrading of heterogeneous catalysts. Economic constraints and common habits in preparing heterogeneous catalysts have narrowed the selection of active-phase carriers to a handful of materials: oxide-based ceramics (e.g. Al2O3, SiO2, TiO2, and aluminosilicates–zeolites) and carbon. However, these carriers occasionally face chemicophysical constraints that limit their application in catalysis. For instance, oxides are easily corroded by acids or bases, and carbon is not resistant to oxidation. Therefore, these carriers cannot be recycled. Moreover, the poor thermal conductivity of metal oxide carriers often translates into permanent alterations of the catalyst active sites (i.e. metal active-phase sintering) that compromise the catalyst performance and its lifetime on run. Therefore, the development of new carriers for the design and synthesis of advanced functional catalytic materials and processes is an urgent priority for the heterogeneous catalysis of the future. Silicon carbide (SiC) is a non-oxide semiconductor with unique chemicophysical properties that make it highly attractive in several branches of catalysis. Accordingly, the past decade has witnessed a large increase of reports dedicated to the design of SiC-based catalysts, also in light of a steadily growing portfolio of porous SiC materials covering a wide range of well-controlled pore structure and surface properties. This review article provides a comprehensive overview on the synthesis and use of macro/mesoporous SiC materials in catalysis, stressing their unique features for the design of efficient, cost-effective, and easy to scale-up heterogeneous catalysts, outlining their success where other and more classical oxide-based supports failed. All applications of SiC in catalysis will be reviewed from the perspective of a given chemical reaction, highlighting all improvements rising from the use of SiC in terms of activity, selectivity, and process sustainability. We feel that the experienced viewpoint of SiC-based catalyst producers and end users (these authors) and their critical presentation of a comprehensive overview on the applications of SiC in catalysis will help the readership to create its own opinion on the central role of SiC for the future of heterogeneous catalysis.

Dimensional Design and Core–Shell Engineering of Nanomaterials for Electromagnetic Wave Absorption

“…In crystallographic SiC, each Si/C atom is surrounded by four C/Si atoms, bonding into an sp 3 ‐hybridized tetrahedron. [ 105 ] The stacking sequences of C–Si double layers in polytypes influence their electric properties, such as the bandgaps of 2.37 eV for 3C‐SiC, 4.04 eV for 2H‐SiC, 3.28 eV for 4H‐SiC, and 3.05 eV for 6H‐SiC. Silicon carbide nanofibers are widely employed as high‐temperature EM wave absorbents by exploiting their 1D structure.…”

Graphite Felt-Sandwiched Ni/SiC Catalysts for the Induction Versus Joule-Heated Sabatier Reaction: Assessing the Catalyst Temperature at the Nanoscale

“…SiC is a semiconductor, non-oxide ceramic featured by good thermal conductivity but not suitable to convert electromagnetic energy into heat (not radiofrequency heatable). 22 To improve the hyperthermic efficiency of the catalytic system, Ni/SiC was sandwiched between two electrically conductive and IH-responsive (eddy or Foucault currents) graphite-felt disks. The comparative analysis of these catalytic materials under different heating configuration (JH vs. IH) and experimental conditions (reaction temperature, gas-hourly-space-velocity -GHSV) has provided a practical tool for mapping the temperature gap existing between the macroscopic value measured at the catalyst bed by the pyrometer and that (real) of the excited metal nano-objects (Ni NPs) directly engaged in the radiofrequency-heated catalytic process.…”

Early Attainments of Porous Silicon Carbide Technology: a Bibliographic Digest

“…Detailed study of the properties of such films was done in [51] According to the Auger electron spectroscopy data, 5+0.5 at.% average deviation from the starting material stoichiometry towards elemental carbon enrichment was determined within the anodic films formed in HF-based electrolytes with ethanol in several concentrations. In addition, an elemental analysis performed with electron diffraction spectroscopy showed that the films were enriched with oxygen and fluorine at the level of (5-7) at.% and (7)(8)(9)(10)(11) at.%, respectively. It was found that the samples with an increased content of detectable chemical impurities had pronounced photosensitivity.…”

“…Here we note that Lee Canham subsequently pioneered the biomedical applications of porous silicon as well [4]. To date, there have been several generalizing reviews on the recent results of obtaining porous structures based on semiconductor materials and compounds and the prospects for their application for modern micro-and nanoelectronics, sensing and biotechnologies [5][6][7][8][9][10][11].…”