Cross-coupling of p-xylene to 2,2′,5,5′-tetramethyl 1,1′-biphenyl on supported vanadia catalysts

• γ-alumina supported vanadia may act as an efficient catalyst for the oxidative cross-coupling of p-xylene.
• The catalyst prepared by citrate method exhibits the higher selectivity.
• The cross-coupling product selectivity is favored by medium acidity.
• The catalytic activity correlates with the density of the vanadia surface species.

Aluminas with different textural characteristics were synthesized by carbonate, citrate and urea sol–gel methods. All supports were impregnated with an aqueous solution of ammonium metavanadate in order to obtain the same loading of vanadia (7% wt V2O5), and then characterized by XRD, N2 physisorption, Raman spectroscopy and NH3-TPD. In this way it was possible to tune the characteristics of the supported vanadia as it has also been demonstrated from the catalytic behavior of these materials in the cross-coupling of p-xylene to 2,2′,5,5′-tetramethyl 1,1′ biphenyl (biaryl) in the presence of O2. Alumina prepared via the carbonate method and calcined at 500 °C proved to be the most suitable support affording, for a level of conversion of 8%, selectivities to biaryl of 96%. It corresponded to an enough high dispersion of vanadium to allow the cleavage of the CH bonds. Recycling experiments confirmed the stability of these catalysts.

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