Mn-Doped material synthesized from red mud and rice husk ash as a highly active catalyst for the oxidation of carbon monoxide and p-xylene

Abstract

Red muad and rice husk ash were treated without neutralization by acid to produce a support material (RR). A series of Mn-doped RRs were prepared by an impregnation method for the catalytic oxidation of CO and/or p-xylene. Various techniques such as X-ray powder diffraction (XRD), Brunauer–Emmett–Teller (BET) nitrogen physisorption measurements, hydrogen temperature-programmed reduction (H₂-TPR), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) were used to characterize the catalysts. XRD and XPS analysis confirmed the existence of Mn₂O₃ in the MnRR1 samples. The addition of Mn₂O₃ into RR led to a decrease in the surface area of RR from 25.6 m² g⁻¹ to 19.0–24.8 m² g⁻¹, pore volume from 0.018 cm³ g⁻¹ to 0.013–0.017 cm³ g⁻¹, and average pore diameter from 20.4 Å to 18.8–20.3 Å, suggesting that Mn₂O₃ can be deposited inside the pores of the material. Among these catalyst samples, 3MnRR1 prepared by 3.0 wt% Mn doped into RR showed the best performance for CO or p-xylene deep oxidation, achieving CO conversion of 100% at approximately 280 °C and p-xylene conversion of 93% at 400 °C. Meanwhile, the conversion of CO and p-xylene in a mixture was found to be much lower than that in a pure substance. An increase in the moisture content was found to lead to lower CO and p-xylene conversion. The obtained catalyst pellet used kaolin as a binder and showed a mechanical strength of 12.4 MPa and a low weight attrition rate of 1.8%. The result indicated that a pellet catalyst had a slightly lower catalytic activity than that in the powder catalyst for CO/p-xylene conversion at the investigated temperatures, the conversions of CO were approximately 98% at 320 °C, and the conversion of p-xylene was 83.8% at 450 °C, and remained almost stable during 50 h of testing. These results confirm that MnRR2 catalytic pellets are promising for industrial catalyst applications.