High surface area Pd, Pt and Ni ion-exchanged Zr, Ti and Sn(IV) phosphates and their application to selective heterogeneous catalytic hydrogenation of alkenes

Abstract

Amorphous acidic metal(IV) phosphates of zirconium, titanium and tin have been prepared and hydrogen-exchanged for bivalent Pd, Pt and Ni. These bivalent metals were returned to the zero valent state by reducing them with either hydrogen at 400 °C or with sodium tetrahydroborate at room temperature. The resulting Pd 0, Pt 0 and Ni 0 phosphates were investigated as selective catalysts for heterogeneous hydrogenation of alkenes in solution at normal temperatures and pressures and, for Ni, also in the vapour phase. Quantitative studies on rates of hydrogenation are discussed. The usual methods for preparing metal(IV) phosphates give either crystalline or amorphous solids having low specific surfaces areas. A method has been developed, by which metal(IV) phosphates having large surface areas (lsa) may be prepared easily. These lsa supports take up large amounts of transition metal cations by simple exchange. The enhanced incorporation of Pd, Pt or Ni and increases in surface areas of the phosphate supports have provided some active, selective catalysts. Pd/Ti phosphates were the most active and compared well with commercial Pd on carbon. Ni/Ti phosphate is a very selective catalyst for vapour phase hydrogenation of alkenes and, at slightly higher temperatures, it is an efficient hydrocarbon cracking catalyst.