Investigation of mechanisms of catalytic reactions using experimental and theoretical methods of physical chemistry

Abstract

The article summarizes modern views on the mechanisms of catalytic transformations determining the formation, functionality, and degradation of building materials, with an emphasis on the integration of instrumental methods of physical chemistry and computational modeling. Multistage processes of hydration of cement binders, polymerization of binders, geopolymerization, photocatalytic self-cleaning of coatings, and biocatalytically induced destruction of polymeric components are considered, for which kinetics under multicomponent heterogeneous media conditions with evolving microstructure is characteristic. Based on the systematization of data on catalytic systems of various natures, it is shown that the reduction in activation energy varies in a wide range of 19.8–65.0% with noticeable heterogeneity of effects: the maximum barrier reduction and the highest acceleration coefficient at 293 K are characteristic of the photocatalytic decomposition of NOₓ on TiO₂, while enzymatic hydrolysis of siloxane bonds provides comparable catalytic efficiency of the same order at a fundamentally different activation mechanism. A comparison of calculated and experimental activation energies for a number of reactions is presented; a systematic tendency to underestimate barriers by the PBE functional and higher predictive stability of B3LYP with an average absolute deviation of about 6% is revealed, which makes hybrid approaches suitable for semi-quantitative screening of additives. The relationships between catalytically induced changes in the microstructure of cement stone and strength are analyzed: a strong inverse correlation between the average pore size and strength at 28 days (r = –0.91) is demonstrated, and a multifactor description through the degree of hydration and porosity characteristics explains the major share of strength variation. For photocatalytic coatings, the multiscale nature of elementary stages is revealed, and it is shown that the low total quantum yield of complete NOₓ conversion of about 0.74% is due to a cascade of recombination and surface transformations, limited by NO₂ oxidation. The presented quantitative dependencies and conclusions allow assessing the relevance of the work for the design of modified binders and functional coatings, as well as for predicting material durability under operational conditions.