Direct Reduction‐Driven Active Species Formation in RuMn‐Containing Zeolite Catalyst for 5‐Hydroxymethylfurfural Oxidation
Rahul Gautam, Rupinder Kaur, Nidhi Gossai, Kanika Saini, Cheralathan Kanakkampalayam Krishnan, Shunmugavel SaravanamuruganABSTRACT
The selective oxidation of 5‐hydroxymethylfurfural (HMF) to 2,5‐furandicarboxylic acid (FDCA) is an important transformation for producing sustainable bio‐based chemicals and polymer precursors. Here, the influence of pretreatment strategies on the physicochemical properties and catalytic performance of RuMn supported on modified H‐ZSM‐5 (RuMn/ZS) was investigated for HMF oxidation. Directly reduced RuMn/ZS (RuMn/ZS‐R) was compared with calcined RuMn/ZS (RuMn/ZS‐C) and calcined‐reduced RuMn/ZS (RuMn/ZS‐CR). RuMn/ZS‐R exhibited the highest activity, affording 72.7% FDCA yield and 75.7% total furanics yield, compared with 5.0% and 14.1% FDCA for RuMn/ZS‐C and RuMn/ZS‐CR, respectively. XPS and TEM analyses revealed that direct reduction promotes highly dispersed metallic Ru 0 species together with Mn 3 + /Mn 4 + promoter species. NH 3 ‐TPD, CO 2 ‐TPD, and in situ diffuse reflectance infrared Fourier transform (DRIFTS) further demonstrated enhanced Lewis and Brønsted acidity and a higher concentration of moderate basic sites in RuMn/ZS‐R. Poisoning experiments supported the contribution of both acidic and basic sites to HMF oxidation. The superior performance of RuMn/ZS‐R is attributed to the synergistic interplay of highly dispersed Ru 0 , Mn promoter species, acidic sites, and moderate basic sites generated by direct reduction. These findings provide insight into designing multifunctional zeolite (ZS)‐supported catalysts for selective biomass oxidation.