Proton affinity distributions of TiO{sub 2}-SiO{sub 2} and ZrO{sub 2}-SiO{sub 2} mixed oxides and their relationship to catalyst activities for 1-butene isomerization
- Syracuse Univ., NY (United States); and others
Proton-releasing properties at the oxide/aqueous solution interface were examined as a function of pH for two series of mixed oxide aerogels and their pure oxide components using potentiometric titrimetry. Reports of synthesis, surface characterization, and catalytic activity (1-butene isomerization) have appeared recently for similar preparation batches of titania-silica and zirconia-silica. After deconvolution of potentiometric titration data, the pK spectra of the oxide surfaces were obtained; they reveal the number and strength of various proton donor sites present under {open_quotes}wet{close_quotes} conditions. The activity in 1-butene isomerization measures weak Bronsted sites of the {open_quotes}pseudo-dry{close_quotes} catalyst (reaction at 423 K after drying at 473 K). We find that the activity for 1-butene isomerization is linearly related to the density of a particular type of proton donor site determined from pK spectra. This shows that only a limited number of the total Bronsted sites accessed by potentiometric titrimetry is specifically active for 1-butene isomerization under the conditions used here. The pK range of active sites and the corresponding TOF numbers are 6.3 {le} pK {le} 8.7, (8.2 {plus_minus} 2.1) x 10{sup {minus}3} s{sup {minus}1} for titania-silica and 6.4 {le} pK {le} 6.5, (93 {plus_minus} 24) x 10{sup {minus}3} s{sup {minus}1} for zirconia-silica. In the two catalysts series the catalytic performance varied with either composition (titania-silica) or preparation parameters (zirconia-silica) at constant composition. 51 refs., 9; figs., 2 tabs.
- DOE Contract Number:
- FG02-92ER14268; FG02-93ER14345
- OSTI ID:
- 183491
- Journal Information:
- Journal of Catalysis, Journal Name: Journal of Catalysis Journal Issue: 1 Vol. 157; ISSN JCTLA5; ISSN 0021-9517
- Country of Publication:
- United States
- Language:
- English
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