Effects of adsorption-active media on the mechanical propreties of catalysts and adsorbents

The mechanical wear, facilitated by the influence of the medium, can be the principal cause of catalyst losses in many heterogeneous catalytic processes. The direct experiments with MgO, Co-Mo, Ca-Ni-P, Al-Cr-K and other catalysts show that both their strength and durability decrease significantly, sometimes dramatically, during catalysis with respect to identical tests in inert media. The effect has been explained as a result of the mutual influence of the solid phase and the medium in catalytic processes: new bonds arising between them may cause bonds weakening and rupture both in adsorbed molecules and in the solid surface (manifestation of the Rehbinder effect). In this aspect, the catalyst is a victim of its destination. However, the resistance of catalyst granules to wear can be essentially improved by perfecting their technology: selection of the optimal size grading of the granule forming particles and strengthening contacts between these particles, using nano-dispersive inactive fillers and hydration hardened mineral binders, reducing residual internal stresses, etc. Catalysis assisted rupture of surface bonds may result also in creating new surface adatoms and, correspondingly, in accelerating the surface self-diffusion and particles sintering, i.e., in the increase in strength, or achieving the same interparticle contacts development and strength at lower sintering temperatures (catalysis enhanced sintering, CES). This has been recently shown both for metal (Fe, Ni) and ceramics (alumina, zirconia, yttria) powder samples.