HAP solids were prepared with different Ca/P ratios and Na⁺cations before being characterized by XRD, XPS, LEIS, NMR, IR, and TGA. Their acid–base properties were then measured and discussed in relation to the characterization results.

The Guerbet reaction of ethanol to produce heavier products was performed over a series of extensively characterized carbonate-containing hydroxyapatites (HAPs) with different Ca/P ratios and thus different densities, strengths and natures of acid and basic sites. These properties were correlated with the reactivity of the solids and an optimal ratio between the amount of acid and basic sites was evidenced (ca. 5). The best performance was accordingly obtained over the Hap-CO₃ catalyst, which gave a yield of 30% of heavier alcohols at 40% ethanol conversion.

Catalytic dehydration of isopropanol to propylene is a common reaction in laboratories to characterize the acid–base properties of catalysts. When acetone is produced, it is the sign of the presence of basic active sites, while propylene is produced on the acid sites. About 2/3rd of the world production of isopropanol is made from propylene, and the other third is made from acetone hydrogenation. Since the surplus acetone available on the market is mainly a coproduct of phenol synthesis, variations in the demand for phenol affect the supply position of acetone and vice versa. High propylene price and low demand for acetone should revive the industrial interest in acetone conversion. In addition, there is an increasing interest in the production of acetone and isopropanol from CO/CO₂ via expected more environmentally friendly biochemical conversion routes. To preserve phenol process economics, surplus acetone should be recycled to propylene via the acetone hydrogenation and isopropanol dehydration routes. Some critical impurities present in petrochemical propylene are avoided in the recycling process. In this review, the selection criteria for the isopropanol dehydration catalysts at commercial scale are derived from the patent literature and analyzed with academic literature. The choice of the process conditions, such as pressure, temperature and gas velocity, and the catalysts’ properties such as pore size and acid–base behavior, are critical factors influencing the purity of propylene. Dehydration of isopropanol under pressure facilitates the downstream separation of products and the isolation of propylene to yield a high-purity “polymer grade”. However, it requires to operate at a higher temperature, which is a challenge for the catalyst’s lifetime; whereas operation at near atmospheric pressure, and eventually in a diluted stream, is relevant for applications that would tolerate a lower propylene purity (chemical grade).