Crystal structure of ammonium dinitrooxalatopalladium(II) and its application as a halogen-free palladium precursor for catalytic VOC oxidation

Supported palladium-based catalysts are widely employed for the catalytic oxidation of volatile organic compounds (VOCs) owing to the exceptional catalytic activity of palladium. However, conventional precursors often contain halogens or exhibit poor aqueous solubility, both of which compromise catalyst performance. The development of highly water-soluble and halogen-free palladium precursors thus remains a critical challenge. In this study, the crystal structure of ammonium dinitrooxalatopalladium(II) hydrate was determined for the first time by single-crystal X-ray diffraction, revealing a monohydrate form ((NH4)2[Pd(NO2)2(C2O4)]·H2O), while elemental analysis and thermogravimetric-differential thermal analysis (TG–DTA) of the powder sample confirmed a dihydrate composition ((NH4)2[Pd(NO2)2(C2O4)]·2H2O). TG–DTA revealed that this compound undergoes decomposition below 190 °C under both oxidative and inert atmospheres, enabling thermal activation under mild conditions. This low decomposition temperature reduces energy consumption during catalyst preparation relative to that required for conventional precursors, while enabling high metal dispersion. Furthermore, a Pd–Pt/γ-Al2O3 catalyst prepared by slurry coating using this precursor was evaluated for the oxidation of CO, CH4, and C3H8. The resulting catalyst exhibited superior catalytic activity compared with a benchmark catalyst derived from palladium nitrate. The enhanced catalytic performance can be attributed to the halogen-free composition and facile thermal activation at temperatures below 190 °C of the precursor, as well as improved palladium dispersion.