Proposed Steps in n-Butane Oxidation to Maleic Anhydride

5 Proposed Steps in n-Butane Oxidation to Maleic Anhydride 

The reaction steps proposed for the transformation of u-butane to maleic anhydride [4] are shown in Table 1. However, none of the intermediates shown in Table 1 was detected under typical reaction conditions for kinetic reasons. 

The activation of secondary C-H bonds in n-butane is the first and ratedetermining step. When compared to oxidation of 1-butene on the VPO catalysts, the rate of n-butane disappearance is 20 [66] to 60 [10] times slower. This may result in a rapid transformation of the intermediates to maleic anhydride before any desorption of the former may occur. 

The following experimental observations led to the proposed reaction steps shown in Table 1  

The unique features of the VPO catalysts in carrying out the reaction steps shown in Table 1 are (i) the ability to selectively activate n-butane during the rate-determining step, (ii) rapid oxidation of chemisorbed intermediates to maleic anhydride with high selectivity, and (iii) the lack of desorption of any intermediate contributing to high selectivity to maleic anhydride. Other cata- 

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