Preparation of metal oxides for effective catalysts

Desired properties in catalysts include a nanosize and homogeneity of the particles that form the catalyst and/or its carrier. The creation of catalysts with the finest particles has been a hot topic of scientific research in recent decades. The particle sizes of catalytic oxides are set at the initial stage of forming; in wet-chemistry, this is a precursor to precipitation. It is possible ot create optimal conditions by using homogeneous precipitation when the precipitant is formed in the solution itself due to a hydrolysis reaction. To solve this problem, urea was used in our work, and the hydrolysis products were ammonia and carbon dioxide. As a result of precipitation, hydroxides, carbonates, or hydroxy carbonates of metals can be obtained.

All precipitates were obtained from solutions of metal nitrates. The obtained hydroxides aluminum, indium, and iron, and the hydroxy carbonates nickel, cobalt, and zinc, were studied. The oxides obtained from these materials by calcination were also studied. They form the structure of the catalyst.

The following was found: metal hydroxides were obtained from aluminum, indium, and iron nitrate solutions. According to the XRD patterns, it was established that the crystallite sizes of the obtained hydroxides were, respectively, 1.5, 10, and 35 nm. The oxides obtained by the calcination of these hydroxides have similar sizes, from 0.6 to 15 nm.

Metal hydroxycarbonates were obtained from nickel, cobalt, and zinc nitrate solutions. The crystallite sizes of these compounds are quite large and exceed 100 nm. However, their thermal decomposition allows us to obtain oxides with crystallite sizes less than 15 nm.

The specific surface area and porosity of several of the obtained samples were also measured. It was found that the obtained oxides have a specific surface area that is significantly higher than similar samples obtained by other methods. Most of the porous volume and surface area is located in the mesopores.