Binding of chromium acetylacetonate on a silica support

Abstract

The binding of vapor on silica pre-heated at 200, 560, and 820 ¡C was studied between 160 and Cr(acac) 3 240 ¡C in a Ðxed bed Ñow reactor by determining the Cr and carbon concentrations, recording FTIR spectra and analyzing the thermal stability of the supported Cr complexes (thermogravimetric analysis and temperature programmed desorption). Saturation of silica with the Cr complex was observed at all reaction temperatures. The saturation density varied from 0.3 to 0.8 Cr nm~2 with variation in the reaction temperature and the pre-treatment temperature of silica (200, 560 or 800 ¡C), evidently determined by the number of available sites on silica and by the size of the Cr complex. At 160 ¡C, both associatively adsorbed and reactedwere concluded to exist. The amount of reacted increased with increase in Cr(acac)3 Cr(acac) 3 reaction temperature, and at 200 ¡C the samples appeared to contain mainly species formed in SiOÈCr(acac) 2 the reaction with isolated OH groups. Samples prepared at slightly higher temperature of 220È240 ¡C also contained partially decomposed acac ligands, denoted Cr acetate species. The ligands of the surface complex could be removed by air treatment with concurrent oxidation of Cr3`to Cr6`surface species. The oxidation was almost complete in the samples prepared at 200È240 ¡C, whereas clustering of Cr3`to occurred in Cr 2 O 3 the samples prepared at 160 ¡C.

Improved Low-Temperature Activity of V2O5-WO3/TiO2 for Denitration Using Different Vanadium Precursors

“…Transition metal acetylacetonate complexes, e.g., VO(acac) 2 [22][23][24][25], Cr(acac) 3 [26], and Cu(acac) 2 [27] have been used as support of catalysts or to prepare thin-film catalyst (acac = acetylacetonate, C 5 H 7 O 2 ). Vanadyl acetylacetonate (VO(acac) 2 ) is shown to be a good vanadium precursor for synthesizing oxovanadium complexes [28][29][30].…”

TPD‐MS and IR Studies of Cr(acac)3 Binding Upon CVD at Silica and Alumina Surfaces

“…The Cr(acac) 3 molecule may bind to the support surface due to formation of hydrogen bonds with hydroxyl groups. [5,11,[15][16][17] In the case of the alumina support, the electron donor-acceptor interaction [4,16] should also be considered. The chemical interaction of Cr(acac) 3 molecules with surface active sites may result in the formation of Cr(acac) x (x < 3) species on the support surface.…”

“…[4][5][6][11][12][13] Since the surface structures of SiO 2 and Al 2 O 3 supports have been very well reported in literature, speculations about Cr(acac) 3 binding at their surface were already being considered. [1,4,5,11,[15][16][17] Currently, two alternative mechanisms of the binding of Cr(acac) 3 at silica and alumina surface active sites are being debated. The Cr(acac) 3 molecule may bind to the support surface due to formation of hydrogen bonds with hydroxyl groups.…”

“…The chemical interaction of Cr(acac) 3 molecules with surface active sites may result in the formation of Cr(acac) x (x < 3) species on the support surface. [1,5,[10][11][12]17,18] The interaction of H-bonded acetylacetonate ligands of Cr(acac) 3 molecules with hydroxyl groups of the silica surface that occurred upon thermal activation in the range 433 À 473 K has been reported. [17,18] It resulted in covalent bonding of Cr(acac) 3 and the formation of SiO-Cr(acac) 2 species.…”

Activation processes and polyethylene formation on a phillips model catalyst studied by laser ablation, laser desorption, and static secondary ion mass spectrometry

“…Therefore, the detection of SiCrO 4-5 Ϫ anions by s-SIMS technique indicates the formation of mixed silicon-chromium species during the activation process. This illustrates the anchorage of chromium oxidized species by reaction with the hydroxyl groups of silica surface [5,25,26].…”