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Supercritical water (SCW) catalytic gasification is a clean and efficient technology with prominent advantages in treating oily wastewater generated in oilfields. SCW synthesis is a promising one-step preparation method for nano-catalytic materials, while the influence of organic matter on SCW synthesis materials remains to be studied. This study focuses on the synthesis of the Ni/ZrO2catalysts by the supercritical water synthesis (SCWS) method, particularly examining how different types and concentrations of organic matter affect the catalysts’ pore information and structural characteristics. It found that glycerol acted as a more effective precursor for generating reducing gases compared to glucose. This is attributed to glycerol’s capacity in SCW to generate reducing gases for activating a greater number of Ni site within the catalyst, and the 5 wt% glycerol should be a proper concentration for SCWS of Ni/ZrO2. When employed in SCW treatment of oilfield wastewater, the Ni/ZrO2catalyst demonstrated impressive results, achieving the carbon gasification efficiency of 99.1 % and a chemical oxygen demand (COD) removal efficiency of 100 % at 500°C. These findings indicate that the SCW technique can effectively and harmlessly treat oilfield wastewater using the Ni/ZrO2catalyst under relatively mild conditions, showing its potential as an innovative solution for wastewater management in the oil industry.

Coal supercritical water gasification (SCWG) is famous for generating clean gas without SOxpollutant. Study of sulfur transformation characteristics can provide the basis of sulfur removal during hydrogen production by coal gasification in supercritical water (SCW) at the source. In this work, two coals produced from Linfen and Zhangjiamao in China (hereinafter to be referred as L-coal and Z-coal), were chosen as experimental feedstocks to investigate sulfur transformation characteristics during hydrogen production by coal gasification in SCW (550–750 °C, 20 min, 25 MPa). Sulfur transformation pathway and sulfur forms in the products were complex but detected comprehensively. H2S was the only gaseous product instead of SOx, whereas SO42–was the main liquid–sulfur product. Inorganic and organic sulfur compounds were used to investigate sulfur transformation mechanisms. H2S had three sources as follows. First, among inorganic sulfur of raw coal, FeS2(Pyrite) was chemically stable in SCW lacking of hydrogen. When FeS2was in hydrogen atmosphere, H2S was generated and FeS2was converted to Fe1–xS and Fe3O4under SCW. Second, H2S came from unstable sulfate minerals such as FeSO4which may decompose and be converted to Fe3O4. Third, organic sulfur, especially thiophene sulfur transformed to H2S. The two sulfur products H2S and SO42–depend on H or OH free radical in SCW. More H free radical provided a reducing environment of SCW to generate H2S at higher temperatures, whereas more OH radical provided an oxidizing environment of SCW to generate SO42–at lower temperatures, but the final trend was generating H2S when coal gasified completely at a higher temperature. The results of this study may provide an experimental basis of solving the SOxemission from coal at the source and demonstrate a promising clean utilization way of coal.

Developing highly stable catalysts at high temperatures while maintaining high activity and selectivity has been a focus of research for propane dehydrogenation (PDH). Herein, we report the catalytic properties of Irδ+sites isolated by phosphorus in iridium phosphide (IrP2) as ultrastable and active catalysts for PDH. Like other transition and main group single-site catalysts, the IrP2catalysts exhibit remarkable propylene selectivity (99%). Notably, the optimized IrP2catalyst has a PDH rate of 0.418 mol C3H6per mole of Ir per second, which represents an approximately 400-fold increase compared to that of Ir NPs and is significantly higher than that of conventional, ionic single-site catalysts. Furthermore, it exhibited a robust stability up to a week with little deactivation. A series of advanced characterizations, including in situ X-ray absorption spectroscopy, scanning transmission electron microscopy, and in situ X-ray photoelectron spectroscopy, elucidated that the isolated Irδ+ions are the active sites for PDH.