T. Zhang, J.P. Croue
Applied Catalysis B: Environmental, volume 144, 831-839, (2014)
Catalytic ozonation, Selectivity, Competitive degradation, Competitive adsorption, Metalcarboxylate complex structure
Catalytic ozonation following non-hydroxyl radical pathway is an
important technique not only to degrade refractory carboxylic-containing
organic compounds/matter but also to avoid catalyst deactivation caused
by metal–carboxylate complexation. It is unknown whether this process
is effective for all carboxylates or selective to special molecule
structures. In this work, the selectivity was confirmed using O3/(CuO/CeO2)
and six distinct ozone-resistant probe carboxylates (i.e., acetate,
citrate, malonate, oxalate, pyruvate and succinate). Among these probe
compounds, pyruvate, oxalate, and citrate were readily degraded
following the rate order of oxalate > citrate > pyruvate, while
the degradation of acetate, malonate, and succinate was not promoted.
The selectivity was independent on carboxylate group number of the probe
compounds and solution pH. Competitive degradation was observed for
carboxylate mixtures following the preference order of citrate, oxalate,
and finally pyruvate. The competitive degradation was ascribed to
competitive adsorption on the catalyst surface. It was revealed that the
catalytically degradable compounds formed bidentate chelating or
bridging complexes with surface copper sites of the catalyst, i.e., the
active sites. The catalytically undegradable carboxylates formed
monodentate complexes with surface copper sites or just
electrostatically adsorbed on the catalyst surface. The selectivity,
relying on the structure of surface metal–carboxylate complex, should be
considered in the design of catalytic ozonation process.