High surface area silicon carbide as catalyst support characterization and stability R. Moene 1 , M. Makkee * , J.A. Moulijn Department of Chemical Process Technology, Section Industrial Catalysis, Delft University of Technology, Julianalaan 136, 2628 BL Delft, Netherlands Received 23 June 1997; received in revised form 20 October 1997; accepted 21 October 1997 Abstract High surface area silicon carbide (SiC) of 30 m 2 /g has been synthesized by the catalytic conversion of activated carbon. The stability of this SiC in aqueous hydrogen ¯uoride and a boiling nitric acid solution is shown to be excellent. No corrosion is encountered by treatment with boiling HNO 3 , HF treatment causes the dissolution of the silica surface layer present on the SiC while the SiC remains intact. Oxidation in air at elevated temperatures has been analyzed by thermal gravimetric analysis, diffuse re¯ectance infrared spectroscopy, nitrogen adsorption, and X-ray diffraction. The thermal stability in non-oxidizing environments is shown to be excellent; no signi®cant sintering has been observed after ageing in nitrogen for 4 h at 1273 K. The presence of 2 v% steam at 1273 K results in partial SiC oxidation into SiO 2 and considerable sintering. Air oxidation at 1273 K of pure SiC, SiC loaded with 5 wt.% nickel, and HNO 3 treated SiC is shown to cause substantial SiC conversion, viz. 60% to 70% after 10 h. Air oxidation at 1080 K will result in complete conversion in about 100 days. This rate of oxidation agrees with reports on the oxidation of non-porous Acheson SiC and SiC coatings formed by Chemical Vapour Deposition. It is concluded that at high surface area SiC cannot be used as a catalyst support in processes operating in oxidizing environments and temperatures above 1073 K. SiC based catalysts are very well suited for (1) high-temperature gas-phase reactions operating in the absence of oxidizing constituents (O 2 or H 2 O) and (2) strong acidic liquid-phase processes. # 1998 Elsevier Science B.V. Keywords: High surface area silicon carbide; Catalyst support; Stability; Oxidation; Chemical vapour deposition 1. Introduction Silicon carbide's physical bulk properties (high thermostability, high mechanical strength, and high heat conductivity) have been claimed to enable the use of this material as catalyst support at extreme process conditions, viz. processes operating at high tempera- tures and oxidizing environments [1]. The application of silicon carbide as catalyst support had mainly been limited by its low maximum attainable speci®c surface area (surface area for a commercially available silicon carbide is below 1 m 2 /g). The last decade, various other methods for the synthesis of high surface area SiC have been reported. The method applied by Applied Catalysis A: General 167 (1998) 321±330 *Corresponding author. Tel.: (+3115) 2781391; fax: (+3115) 2784452; E-mail: m.makkee@stm.tudelft.nl 1 Present address: Shell Research and Technology Centre, Amsterdam, Badhuisweg 3, 1031 CM, Amsterdam, The Nether- lands. 0926-860X/98/$19.00 # 1998 Elsevier Science B.V. All rights reserved. PII S0926-860X(97)00326-8