A THEORETICAL STUDY OF THE THERMODYNAMIC AND KINETIC PROPERTIES FOR THE REACTION OF FORMYL CYANIDE DECOMPOSITION

We compute the thermodynamic and the kinetic properties for the reaction: HCOCN→HCH+CO using the statistical theory and the transition-state theory.The equi- librium constants and the rate coefficients of this reaction are also reported here,and the half lives of formyl cyanide at different temperatures are first estimated in this work.

Thermodynamic Properties of Non-Oxide Composite Refractories

For initiative application of non-oxides in refractories, it is essential to study thermodynamic properties of non-oxides. The stability and stable order of non-ox- ides under oxidized atmosphere are analyzed firstly and then a new process, “converse reaction sintering”, is proposed. The results of study on oxidation mechanism of silicon and aluminum nitrides indicate that the gaseous suboxides can be produced observably when the oxygen partial pressure is lower than “conversion oxygen partial pressure”. The suboxides can be deposited near the surface of composite to become a compact layer. This causes the material possessing a performance of “self-impedient oxidation”. Metal Si and Al are the better additives for increasing the density and width of compact layer and increasing the ability of anti-oxidation and anti-corrosion. The study on Si3 N4-Al2O3, Si3N4-MgO, Si3 N4-SiC systems is also enumerated as examples in the paper. The experimental results show that the converse reaction sintering is able to make high performance composites and metal Si and Al not only can promote the sintering but also increase the density and width of compact layer.

Unlocking power of neighboring vacancies in boosting hydrogen evolution reactions on two-dimensional NiPS3 monolayer

This study investigates the effect of defect engineering on the catalytic activity of a NiPS3 monolayer catalyst for the hydrogen evolution reaction(HER).Three different types of vacancies on the basal plane of the monolayer are explored through a multi-step mechanism involving the dissociative adsorption of a water molecule and subsequent electrochemical adsorption of the dissociated proton.Co-formation of vacancies in both Ni and S sites is found to be the most effective in enhancing the catalytic performance of the monolayer.A key resource for the reaction thermodynamics is the S-substitution-like physisorption of a water molecule on a vacant S site,followed by the dissociative occupation of OH and H into vacant sites of S and Ni elements,boosted by the NiS di-vacancy configuration with low activation energy barriers.Investigation reveals the highest contribution of bonding orbitals to the monolayer-H bond makes it the most desirable defect engineering approach for transition metal phosphorus chalcogenides with high HER activities.Overall,this study highlights the significance of controlled defect engineering in augmenting the catalytic performance of NiPS3 monolayer catalysts for HER.

Diatomic Gaseous Sulfur Obtained at Low Temperature Catalytic Decomposition of Hydrogen Sulfide

Experimental evidences of occurrence of gaseous diatomic sulfur produced in the low temperature catalytic decomposition of hydrogen sulfide 2 H2S ←→ 2 H2 ＋ S2 （g） are summarized. The S2 molecule is suggested to be in the ground triplet state. Analysis of literature data allows concluding that the S2 metastable singlet state is realized in the thermal dissociation of hydrogen sulfide and solid sulfur. Arguments in favor of the hypothesis are been discussed.

Catalysts and thermodynamic coupling of chemical reactions

The condition of occurrence of the thermodynamic coupling of chemical reactions is analysed from kinetics. It is found that the thermodynamic coupling is impossible for those reactions which obey kinetically the mass action law. The thermodynamic coupling of chemical reactions is further analysed in the case with catalyst. It is found that the thermodynamic coupling which is impossible without catalyst may become possible by introducing proper catalyst into the system. This implies that the catalysts can change not only the rates of chemical reactions, but also the behaviors of thermodynamic coupling of chemical reactions, including the direction of some reactions. Such role of catalysts comes into play not by changing the total free energy of the system, but by changing the reaction mechanism.

A critical transition rule for broadening exponent of fluctuation and its effect on dissipation in chemical reaction-heat conduction coupling systems

A stochastic model of chemical reaction-heat conduction-diffusion for a one-dimensional gaseous system under Dirichlet or zero-fluxes boundary conditions is proposed in this paper. Based on this model,we extend the theory of the broadening exponent of critical fluctuations to cover the chemical reaction-heat conduction coupling systems as an asymptotic property of the corresponding Markovian master equation (ME),and establish a valid stochastic thermodynamics for such systems. As an illustration,the non-isothermal and inhomogeneous Schl-gl model is explicitly studied. Through an order analysis of the contributions from both the drift and diffusion to the evolution of the probability distribution in the corresponding Fokker-Planck equation(FPE) in the approach to bifurcation,we have identified the critical transition rule for the broadening exponent of the fluctuations due to the coupling between chemical reaction and heat conduction. It turns out that the dissipation induced by the critical fluctuations reaches a deterministic level,leading to a thermodynamic effect on the nonequilibrium physico-chemical processes.