In situ DRIFTS for the mechanistic studies of 1,4-butanediol dehydration over Yb/Zr catalysts

Zirconium-Based Catalysts in Organic Synthesis

Zirconium is a silvery-white malleable and ductile metal at room temperature with a crustal abundance of 162 ppm. Its compounds, showing Lewis acidic behavior and high catalytic performance, have been recognized as a relatively cheap, low-toxicity, stable, green, and efficient catalysts for various important organic transformations. Commercially available inorganic zirconium chloride was widely applied as a catalyst to accelerate amination, Michael addition, and oxidation reactions. Well-designed zirconocene perfluorosulfonates can be applied in allylation, acylation, esterification, etc. N-Chelating oganozirconium complexes accelerate polymerization, hydroaminoalkylation, and CO₂ fixation efficiently. In this review, the applications of both commercially available and synthesized zirconium catalysts in organic reactions in the last 5 years are highlighted. Firstly, the properties and application of zirconium and its compounds are simply introduced. After presenting the superiority of zirconium compounds, their applications as catalysts to accelerate organic transformations are classified and presented in detail. On the basis of different kinds of zirconium catalysts, organic reactions accelerated by inorganic zirconium catalysts, zirconium catalysts bearing Cp, and organozirconium catalysts without Cp are summarized, and the plausible reaction mechanisms are presented if available.

1,4-Butanediol Selective Dehydration to 3-Butene-1-ol over Ca–Zr–Sn Composite Oxide Catalysts

Ca–Zr–Sn composite oxides catalysts for 1,4-butanediol (BDO) selective dehydration to 3-butene-1-ol (BTO) are synthesized by impregnation and co-precipitation in the present work. The results show that Ca–Zr–Sn catalysts prepared from co-precipitation by using NaOH-Na2CO3 mixing alkali solution as precipitant exhibit an excellent catalytic property for BDO dehydration to BTO. For instance, Ca–Zr–Sn oxide with Ca/Zr and Sn/Zr molar ratio of 0.68 and 0.28 calcined at 650 °C gives a BDO conversion and BTO selectivity of about 97% and 82%, respectively, and exhibits no deactivation during 1000 h scale-up experimental testing. X-ray diffraction results indicate that catalytic active centers for BDO dehydration to BTO are from Ca0.15Zr0.85O crystal phase. NH3- and CO2-temperature programmed desorption prove that the surface of obtained catalysts can provide a large amount of acid and base sites simultaneously. FT-IR spectra of pyridine-adsorbed samples show that acid sites on the surface of Ca–Zr–Sn oxide catalyst mainly exist in a state of Lewis acid, which activates terminal -OH groups of BDO molecule through complexing. The activated -OH interacts with β-H activated on base sites O2− anions relative to Ca species, thereby the CH2=CH- bonds are produced through dehydration to form BTO.