Synthesis of palladium supported on mesoporous hydroxyapatite from oyster shells for use as efficient, green, and recyclable catalyst for Heck reactions

Homogeneous catalysts exhibit several drawbacks, such as high cost, difficulty of separation, and non-recyclability, necessitating the development of heterogenous catalysts to solve these problems. Hydroxyapatite (HAP) can be used as a catalyst carrier owing to its surface acid–base adjustability and strong ion exchange properties. Oyster shell is one of the primary natural sources of hydroxyapatite. The use of cuttlefish bone as a source of hydroxyapatite can also facilitate the recycling of bone waste and reduce the consumption of scarce biological resources and limit environmental pollution. In this study, a heterogeneous catalyst was synthesized by the immobilization of Pd on hydroxyapatite obtained by the hydrothermal method using naturally abundant oyster shells as the calcium source, ammonium dibasic phosphate as the phosphorus source, and cetyltrimethylammonium bromide as the porogen. The synthesized heterogeneous catalyst was characterized using N2-physisorption (adsorption–desorption) measurements, X-ray diffraction analysis, X-ray photoelectron spectroscopy, inductively coupled plasma mass spectrometry, transmission electron microscopy, and temperature-programmed reduction and desorption measurements. The Pd/HAP catalyst shows high catalytic activity for the cross-coupling reaction between iodobenzene and olefins, resulting in yields greater than 67%. Moreover, the Pd/HAP catalyst could be recycled and reused six times with slight reduction in the yield, and thus, is highly stable and recyclable. In addition, it is suitable for use in Heck cross-coupling reactions between various aryl halides and alkenes. Thus, the synthesized catalyst should find extensive use in synthetic chemistry. Graphical abstract