In-situ characterisation of the surface intermediates for the ethanol dehydration reaction over γ-alumina under dynamic conditions

Abstract

The dynamic behavior of the ethanol adsorption on g-alumina were investigated at 180 and 2008C by the transient-response method coupled with FT±IR data of the catalyst surface. The existence of three adsorbates was demonstrated: a reacting species which is the precursor for the formation of the gas-phase ethene; an inhibiting species responsible for the low steadystate reaction rate; and a spectator species accumulating on the catalyst surface. Their infrared spectra indicate an ethoxidelike structure for the three adsorbates. Their C±H stretching bands can be depicted by four Lorentzians whose parameters indicate different surface environments. The surface concentration of the reacting species was determined on the basis of the transient ethene response. A value of 0.77AE0.07 mol/kg cat was found at 1808C. The surface concentration of the spectator species was determined by ex-situ thermogravimetric experiments. A value of 0.13AE0.01 mol/kg cat was found at 1808C. The most likely structure of this species corresponded to an ethanol molecule coordinated in a bidentate manner on Al 3 cations, with stabilisation of the alcoholic-hydroxyl group via lateral hydrogen bonding with an adjacent surface hydroxyl. # 1998 Elsevier Science B.V. All rights reserved.

Mechanistic Studies on the Coupled Reaction of n-Hexane and Ethanol Over HZSM-5 Zeolite Catalyst

“…3a) also gives rise to a broad band at 3,555 cm -1 . This band can be assigned to the OH vibrations of the hydrogen-bonded ethanol [20][21][22][23][24][25]. At the same time, some new bands could also be observed at 2,982, 2,937, 1,448 and 1,395 cm -1 (Fig.…”

“…At room temperature (Fig. 3a), ethanol was adsorbed on HZSM-5 zeolite through interacting with three types of hydroxyl groups (namely terminal silanol groups, AlOH groups and the bridging hydroxyls) to result in three negative absorbances at 3,745, 3,670 and 3,614 cm -1 [17][18][19][20]. Furthermore, the adsorption on bridging hydroxyl groups (Fig.…”

“…3a). These bands can be assigned to symmetric and asymmetric vibrations of the CH 3 groups in the adsorbed ethanol, while the bands at 2,963, 2,905, 2,877 and 2,851 cm -1 can be due to symmetric and asymmetric vibrations of the CH 2 groups [20,[22][23][24][25]. When the temperature was increased from 25 to 100°C, the bands at 3,745 and 3,670 cm -1 disappeared .…”

Role of active components of an Ag/Al2O3/cordierite catalyst in selective reduction of NO by ethanol

“…According to literature data, activation of NO x occurs on the surface of aluminum oxide with formation of adsorbed monodentate, bidentate, and bridged nitrate complexes [1,12]. Since selective reduction of NO by ethanol occurs on the surface of Al 2 O 3 (Table 1), activation of ethanol can occur on Lewis acid sites of aluminum oxide by dehydrogenation [13]. The role of silver in the form of Ag + cations and Ag n d+ nanoclusters is to activate the organic reducing agent by means of its partial oxidation to obtain adsorbed intermediates with high reactivity (in the case of ethanol: enolate (CH 2 =CH-O -) and acetate ions) [3,14], i.e., silver is a redox site for activation of the reducing agent.…”

Drifts and TPD analyses of ethanol on Pt catalysts over Al2O3 and ZrO2—partial oxidation of ethanol

“…Ethoxy species of ethanol were found over different oxide surfaces of TiO 2 (Golay et al, 1998;Yee et al, 1999;Raskó et al, 2006). Raskó et al (2006) studying the adsorption of ethanol over Pt/Al 2 O 3 found negative bands at 3712 and 3680 cm −1 and observed intensity bands (2973, 2928, 2901 and 2884 cm −1 ), which are related to the C-H stretching that above 250…”