Effects of heat treatment on physicochemical properties of cerium based nickel system

摘要

Cerium based nickel catalysts synthesized by impregnation method have been characterized by XRD and TEM techniques. These catalysts can be described as a mixture of nickel oxide and ceria modified by the insertion of a part of nickel in the ceria lattice. The surface and catalytic properties of Ni/Ce mixed oxide solids were determined by nitrogen adsorption at 77 K and catalytic conversion of isopropanol at different temperatures. The results revealed that the heat treatment brought about different modifications in the structural, morphological, surface and catalytic properties of the as synthesized catalysts. From the characterization of the as prepared catalysts, it was concluded that the as prepared catalysts contain highly dispersed NiO, well crystalline NiO and CeO_2 and also Ni-Ce-O solid solution. This treatment led to a slightly increase in the crystallite size of ceria particles. On the other hand, the increase in the heat treatment resulted in an increase in the crystallite size, lattice constant and unit cell volume of nickel oxide. The formation of Ni-Ce-O solid solution with subsequent creation of oxygen vacancies increase as the heat treatment increases. However, the specific surface area, total pore volume and catalytic activity of the investigated system decrease as the preparation temperature increases from 500 to 700℃. The sintering activation energy of NiO and ceria were found to be 2.8 and 12.7 kJ/mol, respectively.