Synthesis and Characterization of Lamellar Precursor-Derived Mixed Metal Oxides for Enhanced Catalytic Toluene Oxidation

The hydrothermal method was used for the synthesis of lamellar chromates and vanadates of Cu and Ni (ΦY and ΦZ -types), which served as precursors for the subsequent synthesis of mixed metal oxides (MMO). These MMOs (named as CuV MMO, NiV MMO, CuCr MMO, and NiCr MMO) were characterized and evaluated for the catalytic oxidation of toluene, showing activity at temperatures below 400 °C. Among the studied materials, CuCr MMO demonstrated superior catalytic activity compared to CuV MMO, NiCr MMO, and NiV MMO, due to the higher reducibility of Cu or Cr in these materials. The temperatures required to achieve 90% conversion of toluene (T90) followed the order CuCr MMO (~275 °C) < CuV MMO (~330 °C) < NiV MMO (~370 °C) < NiCr MMO (~395 °C). Furthermore, the incorporation of Co to CuCr MMO (which produced CoCuCr MMO) significantly improved the catalytic performance, leading to toluene oxidation at even lower temperatures, T90: ~265 °C. For comparison, the MMO derived from the lamellar precursor exhibited superior catalytic performance relative to that obtained via simple mixing and calcination of the corresponding inorganic metal salt. This result highlights the relevance of the precursor’s structure in the subsequent catalytic activity. Finally, a stability test was performed on the best-performing catalytic material (CoCuCr MMO). Toluene conversion remained at ~100% for the first 4 h, then decreased to ~45%, remaining stable for up to 70 h of continuous reaction.