Preparation and characterisation of diatomaceous earth/MnMo₉O₃₂ system and its potential application in clean oxidation

Heteropolyanions containing molybdenum and/or tungsten are an important class of compounds with properties such as high reactivity, selectivity, and structural diversity. In the present study, the heteropolymolybdate Waugh type containing Mn(II) as a heteroatom, (NH₄)₆MnMo₉O₃₂ (MnMo₉), was studied as a supported catalyst, using diatomaceous earth from northwestern Argentina as the support. The diatomaceous earths are highly adsorbent porous materials. Also, they are inexpensive and widely available in the pre-Cordillera region of Argentina. The HPOM and supported systems were characterised by DRX, FTIR, SEM-EDS, and RTP, among other physicochemical techniques. Given the chemical and structural properties of this phase, the clean oxidation of diphenyl sulfide (DFS) was chosen as the catalytic reaction for system evaluation. The reaction products, diphenyl sulfoxides (DPSOs) and diphenyl sulfones (DPSO₂), are of great interest as intermediates in the fine chemical and pharmaceutical industries. Diphenyl dulphide also acts as a test molecule for the study of processes to obtain ultra-low-sulphur fuels.
The MnMo₉ system was evaluated as a bulk and a support in the oxidation of DPS with H₂O₂, as a clean oxidant, at 80 °C. The results for the supported phase showed high reactivity, and a conversion of 100% of DPS was achieved at longer reaction times, with good selectivity for diphenyl sulfone at short reaction times.