Molybdenum blue nano-rings: an effective catalyst for the partial oxidation of cyclohexane

Abstract

Molybdenum blue (MB), a multivalent molybdenum oxide with a nano-ring morphology is well-known in analytical chemistry but, to date it has been largely ignored in other applications.

Insights into the Reaction Mechanism of Cyclohexane Oxidation Catalysed by Molybdenum Blue Nanorings

“…In particular, MB had the interesting property to be is selective towards the formation of cyclohexanol rather than cyclohexanone and with minimal formation of adipic acid (the three major products of cyclohexane oxidation) [9]. Furthermore, this was achieved under reaction conditions (T = 140 o C, and P = 3 bar of O 2 ) that are similar to those industrially employed for the oxidation of cyclohexane using a cobalt naphthenate initiator [10].…”

“…It was found that treating Previous characterization of these materials by means of XRPD and HRTEM showed that the thermal treatment left the three-dimensional structure of the nanoring unaltered [9]. However, XPS data showed a change in the Mo 5+ /Mo 6+ ratio from 0.28 for MB, to 0.42 for T-MB, [9] thus presenting an increase in Mo 5+ centres i.e.…”

“…A further feature of interest in this material is the presence of Mo 5+ -O-Mo 6+ units embedded into the nanoring structure [8], a property that we exploited showing that MB can be an efficient catalyst for the oxidation of cyclohexane [9]. In particular, MB had the interesting property to be is selective towards the formation of cyclohexanol rather than cyclohexanone and with minimal formation of adipic acid (the three major products of cyclohexane oxidation) [9].…”

“…Molybdenum blue (MB) was prepared following with the procedure reported in [9] and references therein. Molybdenum metal powder (Sigma, assay 99.99% wt) was mixed with diluted hydrogen peroxide (Aldrich 30 wt%, trace metals < 10 ppm) and the suspension was stirred for 8 h at room temperature.…”

“…Indeed, this is a crucial step for the manufacture of nylon fibres, with cylohexanol used as precursor for nylon-6,6 and cylohexanone as precursor for nylon-6. [13] Current data suggest that for the oxidation of cyclohexane, MB is able to activate a true catalytic reaction pathway [9], rather than a promoted autoxidation as in the case of Co salts [14]. This prompted us to investigate the mechanistic features of this reaction in presence of MB and as a function of the amount of Mo 5+ -O-Mo 6+ bridges.…”