Applied Catalysis B: Environmental 47 (2004) 111–126 High surface area chromia aerogel efficient catalyst and catalyst support for ethylacetate combustion H. Rotter a , M.V. Landau a,∗ , M. Carrera b , D. Goldfarb b , M. Herskowitz a a Blechner Center for Applied Catalysis and Process Development, Chemical Engineering Department, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel b Department of Chemical Physics, Weizmann Institute of Science, Rehovot 76100, Israel Received 23 March 2003; received in revised form 25 May 2003; accepted 2 August 2003 Abstract The effect of dispersion and ensembling mode of chromium oxide nanocrystals in bulk xerogels and aerogels on their performance as well as efficiency of high surface area chromia aerogel as catalysts support were investigated in complete ethylacetate (EA) oxidation. Two series of chromia catalysts with a structure of -Cr 2 O 3 (7–110 m 2 g -1 ) and -CrOOH (230–735 m 2 g -1 ) were tested in EA complete oxidation as a model reaction for VOC combustion. For -Cr 2 O 3 , the specific activity increased 3.3 times with decreasing the crystal diameter from ∼100 to 13 nm. For -CrOOH materials, where the surface area was determined by the different packing mode of primary nanoparticles of the same size (3–5 nm), the similar specific rate constants were measured with all the tested samples. The activity of the chromia aerogel (-CrOOH, 630 m 2 g -1 ) was four times higher compared with 0.5% Pt/Al 2 O 3 and 30 times higher relative to 30% Cr 2 O 3 /SiO 2 . Oxidative treatment (O 2 ) at elevated temperatures converts both phases to CrO 2, in case of -Cr 2 O 3 —only in the crystals surface layer. In both reduced and oxidized states, high concentration of surface oxygen vacancies were detected in -Cr 2 O 3 and -CrOOH catalysts. A redox cycle Cr(III)[ ]OH ↔ Cr(IV)[O]O which determines the catalysts performance at the surface of both types of bulk chromia materials was proposed. Promotion of high surface area chromia aerogel with Pt, Au, Mn and Ce increased its activity in EA complete oxidation by a factor of 1.25–2.7. Addition of Pt, Mn to ceria-promoted chromia aerogel has a significant effect, yielding a high specific rate constant. Promotion with Ce- and Mn-additives improved the efficiency of redox cycle in Cr-aerogel and increased the concentration of surface oxygen vacancies. © 2003 Elsevier B.V. All rights reserved. Keywords: Aerogels; Catalytic combustion; Chromium catalysts; Ethyl acetate; Volatile organic compounds 1. Introduction The emission of industrial volatile organic compounds (VOC) to the atmosphere is a subject of strict legislation due to increased concern about the photochemical smog, ground level ozone and toxic air emissions [1–4]. Heterogeneous catalytic combustion of VOC in air with solid catalysts op- erating at 200–450 ◦ C and short residence time (<1 s) is the most efficient method [3–6]. It is fuel efficient and pro- duces less NO x emission operating in smaller and lighter units with greater operational flexibility. The efficiency of catalytic VOC oxidation is determined by catalysts activity, selectivity and stability, so further catalysts improvement is required. ∗ Corresponding author. Tel.: +972-8-6472141; fax: +972-8-6477678. E-mail address: mlandau@bgumail.bgu.ac.il (M.V. Landau). The commercial catalysts for VOC combustion contain noble metals, transition metal oxides (TMO) or their com- binations stabilized in a high dispersion state at the surface of refractory oxides like highly porous alumina or silica [1,6–12]. The noble metal catalysts are more active and tol- erant to poisons [1,6]. The most practical catalysts contain Pt or Pd alloyed with Ru, Rh or Ir that stabilizes the sys- tem to sintering at high temperatures [1]. Among the most active TMO in complete oxidation are oxides of Cr, Mn, V, Co and Cu [1,12,13]. They display lower activity compared with noble metals but are more efficient on cost basis. Two issues have been raised in the ethylacetate EA combustion on supported chromia catalysts [12]: blocking of pores with active phase, which limits metal loading to ∼30 wt.%; and low efficiency of TMO redox cycle due to metal oxide–support interaction. Using pure nanostructured TMO with high surface area could resolve those issues. 0926-3373/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.apcatb.2003.08.006