The production of long chain olefins from fatty acids via decarbonylation is limited by low olefins selectivity at high conversion. Here, we reported the direct acid-to-olefins conversion via the ketonization-hydrogenation-dehydration sequence at 400 degrees C and atmospheric 10 %H-2/Ar. The oxygen vacancy defects (V-O) were essential in acetic acid ketonization over the oxygen-deficient alkali hexatitanate A(2)Ti(6)O(13-x) (A=K, Na and Li) catalysts, as evidenced from the activity of reduced vs non-reduced catalysts. The presence of V-O was deduced spectroscopically with XPS and DRUV-VIS, and the ease of V-O formation was ranked via the DFT calculations. The ketonization activity was proportionated to the square of the V-O content (x(2)), consistent with the bimolecular reaction mechanism. The Pt-loaded K2Ti6O13-x enabled the direct acid-to-olefins transformation as shown by a complete conversion of two model compounds (heptanoic acid and lauric acid) with similar to 30-40 % yield of long chain olefins. Heptanoic acid (C-7) underwent ketonization to 7-tridecanone (a C-13 ketone) prior to the hydrogenation-dehydration to 7-tridecene, a C-13 olefin. The strong metal-support interaction (SMSI) between Pt and K2Ti6O13-x inhibited further hydrogenation of the olefin to a low-value alkane. For lauric acid (C-12), 12-tricosene (a C-23 olefin) was produced analogously. The catalytic activity and products selectivity over Pt-loaded K2Ti6O13-x significantly depended on the Pt content (0-1.0 wt%). The simultaneous C-C coupling and oxygen removal prior to the subsequent hydrogenation and dehydration is a potential approach toward the production of long chain olefins with the (2n-1) carbon atoms from C-n-fatty acids.