Heterogeneous catalyst structure and function: review and implications for the analysis of dissolved organic carbon and nitrogen in natural waters

Abstract

It is the purpose of this paper to provide a brief summary of some of the fundamental concepts of the general chemistry of heterogeneous catalysts, several of which have been recently employed in high-temperature flow-through reactor systems for the analysis of dissolved organic matter in seawater. To avoid the application of these high-temperature catalytic oxidation (HTCO) techniques in an entirely ‘black box’ manner, it is imperative that the chemical oceanographic community be aware of the structure and function of heterogeneous catalysts, of the advances which have been made in developing such catalysts, and of the inherent limitations to their use as quantitative tools. The information presented herein has been adapted in part from several excellent recent texts and reviews on various aspects of catalyst chemistry, and the interested reader is encouraged to refer to them for greater detail on the subjects touched upon here. Four general topics will be covered in this review. First, the component parts of heterogeneous catalysts will be defined and the relative advantages and disadvantages of different materials for purposes of organic carbon and nitrogen oxidation will be evaluated. Second, the synthesis and subsequent structure-function relationships of catalysts relative to the reactions carried out will be briefly discussed. Third, those factors known to be responsible for the deterioration of catalytic function and for short-and long-term catalyst deactivation will be assessed. Finally, we will discuss and speculate upon numerous aspects of the application of these catalysts for the specific purpose of accurately quantifying the dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) in seawater. These final two categories will include information obtained from our recent efforts to design and employ different alumina- and aluminosilicate-based catalysts in HTCO systems.