Synthesis, characterization, and catalytic activity of alkali metal molybdate/α-MoO3 hybrids as highly efficient catalytic wet air oxidation catalysts

• Three M2Mo4O13/α-MoO3 (M = Li, Na or K) hybrids were hydrothermally synthesized.
• The hybrids showed high activity for the catalytic wet air oxidation of dyes.
• The synthesis pH plays a great role on the composition and morphology of hybrids.
• M2Mo4O13 is crucial for the high catalytic activities of the M2Mo4O13/α-MoO3 hybrids.

To develop new catalysts which can be used in catalytic wet air oxidation (CWAO) with ambient temperature and atmospheric pressure, a series of M2Mo4O13/α-MoO3 (M = Li, Na or K) hybrid catalysts for cationic red GTL removal were synthesized by a facile hydrothermal method. The growth of crystals under different synthesis pH and the phase evolution during thermal treatment were carefully monitored using various analytical tools. The influence of synthesis pH, calcination temperature, reaction temperature, degradation time, and bubbling with air or N2 on the decolorization efficiency, and the removal rates of total organic carbon (TOC) and chemical oxygen demand (COD) were systematically investigated. For all three catalysts, approximately 100% of color and over 93% of TOC could be removed within 30 min. Compared to many catalysts reported in literature, these novel catalysts showed higher catalytic activity in dye wastewater degradation. The catalytic activity tests in the presence of 2,2,6,6-tetramethyl-1-piperidinyloxy-N-oxyl (TEMPO) and the electron spin resonance (ESR) analysis suggested that the existence of M2Mo4O13 (M = Li, Na or K) promotes the formation of OH radicals and is critical for their superior catalytic activity. Considering the ambient operating condition and the excellent catalytic activity, these novel CWAO catalysts are very promising for practical applications.

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