On the intermediates of the acetic acid reactions on oxides: an IR study

Ketonisation of carboxylic acids over Zn-Cr oxide in the gas phase

“…Fig. 8 shows the DRIFT spectrum of acetic acid adsorbed on Zn-Cr (10:1) oxide measured in the absence of acetic acid in the gas phase after evacuation at 160 • C. This spectrum is similar to those reported previously for other metal oxides [25][26][27][28][29]. The absence of a peak characteristic of the C O stretch in the region of 1690-1790 cm −1 clearly shows that there is no physisorbed acetic acid present.…”

“…The peaks at 1424 and 1351 cm −1 can be assigned to C-H deformations. The bands at 1553 and 1462 cm −1 can be attributed to the antisymmetric and symmetric vibrations of the OCO group of acetate [25][26][27][28][29], which indicates the bridging mode for acetate bonding (Scheme 1) [29].…”

“…Numerous IR spectroscopic studies have dealt with carboxylic acid adsorption on metal oxides, e.g., TiO 2 , Al 2 O 3 , CeO 2 , SnO 2 , and MgO [25][26][27][28][29]. There is compelling evidence that carboxylic acids adsorb dissociatively on a pair of the neighbouring Lewis acid and base sites on the metal oxide surface to form a metal carboxylate in monodentate, bidentate chelate or bidentate bridging bonding mode.…”

Catalytic Deoxygenation of Methyl-Octanoate and Methyl-Stearate on Pt/Al2O3

“…For example, TPD studies of preadsorbed carboxylic acid on metals indicate that the selectivity to decarboxylation or decarbonylation depends on the metal-oxygen bond strength, which explains some of the activity trends observed on different metals [12]. In related work [13][14][15], researchers have found that the best catalyst for hydrogenation of a carboxylic acid to aldehyde/alcohol was a combination of a partially reducible oxide such as SnO 2 or TiO 2 with a noble metal, such as Pt. Oxygen removal occurs on the reducible oxide via an oxygen vacancy mechanism, while the metal provides dissociated hydrogen to reduce the oxides [16].…”

Comparison of the liquid and gas phase photocatalytic activity of flame-synthesized TiO2 catalysts: the role of surface quality

“…This is caused by the higher degree of interfacial accumulation of the intermediates as they are particularly well-adsorbing compounds. Formic and acetic acid can bind strongly to Lewis acid sites in uni-as well as in bi-dentate mode through the lone pairs of the two oxygen atoms [27,28]. At sufficiently high coverage, this strong interaction effectively hinders the adsorption of acetaldehyde [29,30], therefore the oxidation route via radicals starts to prevail.…”