Direct and efficient transformation of gaseous alkanes into carboxylic acids catalyzed by vanadium containing heteropolyacids

Abstract

Abstract The vanadium containing heteropolyacids H 4 [PMo 11 VO 40 ] × 34H 2 O ( HPA-1 ), H 5 [PMo 10 V 2 O 40 ] × 32H 2 O ( HPA-2 ) and H 6 [PMo 9 V 3 O 40 ] × 34H 2 O ( HPA-3 ) act as highly active catalysts for the direct transformation of light C 1 –C 3 alkanes into the corresponding carboxylic acids in the presence of CO and in the K 2 S 2 O 8 /CF 3 COOH system. Propionic acid (ca. 70% yield), iso - and n- butyric acids (ca. 65% overall yield), and acetic acid (ca. 20%) are the major products obtained from the carboxylation of ethane, propane and methane, respectively, with vanadium playing a main catalytic role. The effects of the catalyst amount have been studied and overall turnover numbers (TONs) up to ca. 12 × 10 3 (for the ethane and propane conversions) or up to 3 × 10 3 (for the methane carboxylation to acetic acid) have been achieved for very high alkane-to-catalyst molar ratios which also promote the selectivity towards acetic acid.