IN-SITU FTIR SPECTROSCOPIC STUDIES OF ELECTROOXIDATION OF C-4 ALCOHOLS ON PLATINUM-ELECTRODES IN ACID-SOLUTIONS - PART II - REACTION-MECHANISM OF 1,3-BUTANEDIOL OXIDATION

The electrooxidation of 1,3-butanediol (1,3-BD) on platinum electrodes in perchloric and sulphuric acid solutions was studied by using cycli c voltammetry and in situ FTIR spectroscopy. The determination of inte rmediates and products involved in 1,3-BD oxidation was carried out in solutions prepared using either millipore water or deuterated water a s 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 determine d in 1,3-BD oxidation. The first one is the dissociative adsorption of 1,3-BD, which yields CH3CHOHCH3 and poison species COad. The second o ne is the dehydration of 1,3-BD, which produces intermediates of CH3CH =CHCH2OH and CH2 =CHCH2CH2OH. The last one is the direct oxidation of 1,3-BD at potentials above 0.30 V(SCE) on a Pt surface free of COad, w hich produces intermediates of CH3CHOHCH2COOH and CH3COCH2CH2OH. These intermediates are characterised by IR bands appearing near 2045 (COad ), 1600 (> C=C <), 1720 cm(-1) (> C=O) and a series of IR bands locati ng in the fingerprint region and around 3000 cm(-1). Ah the above inte rmediates can be oxidised further to acid compounds, among them acetoa cetic acid which is characterised by the double carbonyl bands at 1724 and 1712 cm(-1) and has been determined as the majority species. As t he acid compounds can be oxidised to CO2 which yields IR absorption at 2345 cm(-1) via a C-C bond breaking process at relatively high electr ode potentials, they have been considered to play the role of both int ermediate 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 CO2. Th e comparison of IR features of 1,3-BD oxidation with those of l-butano l oxidation reported in our previous paper [1] illustrated the effects of molecular structure in electrocatalysis of C-4 molecules. (C) 1998 Elsevier Science S.A. All rights reserved.