PdAu-catalyzed oxidation through in situ generated H₂O₂ in simulated produced water

Most wastewater recovered from hydraulically fractured oil and gas wells (i.e. produced water) is transported to government-permitted, salt-water disposal units (SWDs) and discarded via downhole injection. However, there is a limited availability of disposal wells in some states and growing interest over future options for beneficial reuse. One alternative to using SWD facilities is to recycle the water for further use in oilfield operations. Residual oil and grease are one contaminant class in produced water where cost-effective treatment technologies are lacking. In this work, we studied the ability of alumina-supported bimetallic PdAu to degrade organic compounds at room temperature and atmospheric pressure via the catalytic formation of H₂O₂. Similar to monometallic Pd and Au catalysts, the PdAu catalyst produced H₂O₂ and hydroxyl radicals in the presence of oxygen and formic acid. The bimetallic catalyst was the most active in terms of initial ^[rad]OH formation rate, and when phenol was present, PdAu showed the highest rate of phenol degradation. We assessed the promotional and inhibitory effects of other species present in produced water including ferrous ion concentration, pH and salt concentration on catalytic phenol oxidation. PdAu was catalytically active for phenol degradation in simulated produced water at salinities as high as ˜0.3 M (˜16,000 ppm). The combination of air-formic acid-bimetallic catalyst is an intriguing approach for the degradation of organics in contaminated water at low pH and moderate salinity.