Thermal reactions involving solids: a personal view of selected features of decompositions, thermal analysis and heterogeneous catalysis

Abstract

AbstractConvinced that some recent trends in the literature concerned with reactions involving solids have been unproductive, even discouraging interest in the subject, this reviewer analyses the reasons and charts a way forward. In particular, two topics are discussed: thermal analysis and activation energy. Thermal analysis, automated collection and interpretation of kinetic data for solid(?)-state decompositions, resulted in huge numbers of publications between late 1970s and 2010. Measurements were frequently minimalistic (few, often no, confirmatory tests complemented rate data). Kinetic data interpretations were based on the Arrhenius activation model, inapplicable to these assumed, usually unconfirmed, solid-state(?) reactions. Energy distributions within crystalline reactants differ from those of ‘free-flying’ gaseous reactants, and thus, mechanistic proposals are entirely speculative. Such studies yielded little more than the reaction temperature: no meaningful insights into reaction chemistry, controls, mechanisms. Despite my several highly critical articles, these inconsequential studies continued. Overall, this now sidelined topic impacted adversely on solid-state chemistry, activation energy, E. Concurrently with the above studies, L'vov published a theoretical explanation for the magnitude of E: the Congruent Dissociative Volatilisation (CDV), thermochemical approach. This was also ignored by the ‘Thermoanalytical Community’, possibly because it assumes an initial volatilisation step: it appears that many solid-state scientists are prejudiced against mechanisms involving a phase change. The value of this novel theory (CDV) in identifying controls and mechanisms of solid-state reactions is discussed here. This review is positive: an interesting branch of main-stream chemistry remains open for exploration, expansion, explanation and exploitation!