In situ FTIR spectroscopic studies of electrooxidation of C4 alcohols on platinum electrodes in acid solutions

The electrooxidation of 1,3-butanediol (1,3-BD) on platinum electrodes in perchloric and sulphuric acid solutions was studied by using cyclic voltammetry and in situ FTIR spectroscopy. The determination of intermediates and products involved in 1,3-BD oxidation was carried out in solutions prepared using either millipore water or deuterated water as solvent. The in situ FTIRS data acquired from experiments of single potential alteration and time-resolved determination demonstrated that the oxidation of 1,3-BD on the Pt electrode is a complex process and may obey a dual path reaction mechanism. Three pathways were determined in 1,3-BD oxidation. The first one is the dissociative adsorption of 1,3-BD, which yields CH 3 CHOHCH 3 and poison species CO ad . The second one is the dehydration of 1,3-BD, which produces intermediates of CH 3 CHCHCH 2 OH and CH 2 CHCH 2 CH 2 OH. The last one is the direct oxidation of 1,3-BD at potentials above 0.30 V(SCE) on a Pt surface free of CO ad , which produces intermediates of CH 3 CHOHCH 2 COOH and CH 3 COCH 2 CH 2 OH. These intermediates are characterised by IR bands appearing near 2045 (CO ad ), 1600 (>CC −1 (>CO) and a series of IR bands locating in the fingerprint region and around 3000 cm −1 . All the above intermediates can be oxidised further to acid compounds, among them acetoacetic acid which is characterised by the double carbonyl bands at 1724 and 1712 cm −1 and has been determined as the majority species. As the acid compounds can be oxidised to CO 2 which yields IR absorption at 2345 cm −1 via a C–C bond breaking process at relatively high electrode potentials, they have been considered to play the role of both intermediate and product in 1,3-BD oxidation. The ultimate product of 1,3-BD oxidation at potentials above 0.30 V(SCE) is determined as CO 2 . The comparison of IR features of 1,3-BD oxidation with those of 1-butanol oxidation reported in our previous paper [1] illustrated the effects of molecular structure in electrocatalysis of C 4 molecules.