A systematic study investigating the effects of water matrices on heterogeneous catalytic ozonation processes was conducted in a semibatch reactor at initial pH 7.00 +/- 0.20. Specifically, three matrices commonly used in laboratory studies were tested: deionized (DI) water, phosphate buffered solution, and tetra-borate buffered solution. Three metal oxide catalysts on SiO2 support, CuO/SiO2, Fe2O3/SiO2, and MnO2/SiO2 (all similar to 4.5% metal loading), were synthesized and used as representative solid catalysts. Oxalate was selected as the model compound as it is a common end product in aqueous ozonation processes and also a typical refractory compound to conventional chemical oxidation. Hydroxyl radical (center dot OH) is generally accepted as the main reactive species in catalytic ozonation processes and can react with oxalate by electron transfer. Catalytic ozonation of oxalate in different water matrices were carried out in a laboratory experimental setup where ozone concentrations in the feed gas and off gas line were continuously monitored. Decomposition tests with and without catalysts in different matrices were also conducted in batch homogeneous reactors to probe the matrix effects on ozone decomposition and interactions between ozone and the catalysts. Moreover, t-butanol (TBA) and methanol were added as the center dot OH probe compounds to investigate the oxalate degradation mechanisms in various matrices. It was found that the effects of water matrices on catalytic ozonation were multifaceted, including process performance, catalysts stability, and mechanism and reaction pathways. These matrix effects can be ascribed to the influence of inorganic anions such as phosphate and borate on ozone decomposition, competitive adsorption on the catalyst surface, and generation of reactive species during catalytic ozonation processes.