Environmental Engineering Reference
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1993, 1994; Iwasita et al., 1994; Schmidt et al., 1999a; Lima et al., 2001; Jusys et al.,
2002a, b; Ge et al., 2001; Basnayake et al., 2006].
More quantitative predictions of the reaction characteristics require a detailed
understanding of the oxidation kinetics of the different C 1 molecules, and in particular
of the product distribution in the respective oxidation reactions under defined reaction
conditions and, most importantly, under defined transport conditions. The latter affect
both the delivery of educts and the removal of products and side products (incomplete
oxidation products). This is the topic of the present study, where we have investigated
the reaction kinetics and product distribution for the oxidation of the C 1 molecules
methanol, formaldehyde, and formic acid by comparative differential electrochemical
mass spectrometry (DEMS) measurements under well-defined, but nevertheless
close-to-realistic conditions and materials (supported catalyst, and continuous and
controlled reactant transport). In contrast to purely electrochemical measurements,
DEMS allows one to directly detect the volatile reaction products CO 2 and methyl
formate. The latter is produced in proportion to the formic acid concentration and
results from reaction between the reactant methanol and formic acid (see the next
section). Formaldehyde formation is determined as the difference between the total
faradaic current and the partial currents for CO 2 and formic acid formation, assuming
that these are the only products contributing to the faradaic current. Defined transport
conditions were achieved by using (i) a thin-layer flow cell DEMS setup [Jusys et al.,
1999, 2001] and (ii) thin-film electrodes with negligible internal diffusion resistance
[Schmidt et al., 1998]. The first results of this study, focusing on the adsorption and
oxidation of methanol on a carbon-supported Pt (Pt/C) fuel cell catalyst [Jusys and
Behm, 2001] and on the effect of Pt catalyst loading on the MOR product yields
[Jusys et al., 2003] were reported previously; additional measurements on unsup-
ported Pt and PtRu nanoparticle catalysts were published in [Jusys et al., 2002a, b].
There are a number of excellent reviews of the numerous studies on methanol
oxidation on Pt electrodes and catalysts [Lamy et al., 1983; Parsons and VanderNoot,
1988; Sun, 1998; Jarvi and Stuve, 1998; Cohen et al., 2008; Iwasita, 2002, 2003].
Most importantly, these studies showed the formation of formaldehyde and formic
acid as incomplete oxidation products, in addition to the complete oxidation product
CO 2 . These species were detected by chemical analysis [Petukhova et al., 1977; Ota
et al., 1984; Korzeniewski and Childers, 1998; Childers et al., 1999; Batista et al.,
2003, 2004], transmission infrared (IR) spectroscopy [Gao et al., 2004; Islam et al.,
2007], and online mass spectrometric analysis [Iwasita and Vielstich, 1986; Wang
et al., 2001a, b; Jusys et al., 2002a, b; Housmans et al., 2006; Iwasita, 2002, 2003;
Wonders et al., 2006; Wang and Baltruschat, 2007], while adsorbed reaction intermedi-
ates (mainly CO ad ) were detected by in situ techniques such as IR spectroscopy
[Sanicharane et al., 2002; Tkach et al., 2004; Sun and Clavilier, 1987; Nakamura
et al., 2007; Christensen et al., 1988; Perez et al., 1994; Fan et al., 1996; Xia
et al., 1997; Waszczuk et al., 2001; Zhu et al., 2001; Park et al., 2002a; Coutanceau
et al., 2002; Yajima et al., 2004], nuclear magnetic resonance (NMR) [Rice et al.,
2000], or radiotracer [Waszczuk et al., 2001; Coutanceau et al., 2002; Sobkowski
and Wieckowski, 1972; Kazarinov et al., 1975] methods. In addition to these exper-
imental studies, the dehydrogenative adsorption/oxidation of methanol on a Pt(111)
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