Reaction of ethanol over hydroxyapatite affected by Ca/P ratio of catalyst

The mineral hydroxyapatite [HAP; Ca10(PO4)6(OH)2] is the chief component of animal bones and teeth. It also is known to function as a catalyst with both acid and base sites, depending on the manner in which it is synthesized. We closely studied the reaction of ethanol over HAP using catalysts of different Ca/P molar ratios. These were prepared by controlling the pH of the solution during precipitation synthesis. We found that the distribution of acid sites and basic sites on the catalyst surface varied with the Ca/P ratio of HAP. The yields of ethylene, 1-butanol, and 1,3-butadiene were correlated with the ratio of acid sites and basic sites. We further found that yields of higher alcohols, such as 1-butanol, that are known as Guerbet alcohols and are characteristic products of ethanol over HAP, are functions of the probability of ethanol activation (α) on the catalyst surface.