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The kinetic models based on complex free-radical mechanisms always involve lots of parameters, which result in model overparameterization. In this work, on the basis of free-radical reaction mechanisms, a simplified kinetics for liquid-phase catalytic oxidation of p-xylene (PX) to terephthalic acid (TPA) was developed. By assuming that different peroxy radicals have equivalent reactivity, all the initiation rate constants are identical, and the differences in the rates of termination between various peroxy radicals are neglected, the kinetic model is simplified to include only six parameters that are to be determined by experiment. The kinetic model established in this paper was shown to have satisfactory precision in predicting the concentration profiles. The kinetic model proposed is even simpler than the first-order kinetic model because the rate constants concerning chain propagation and termination are independent of temperature within the range investigated.

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A series of Cu–SAPO-18 catalysts with various Cu loadings were prepared and their catalytic activities were tested for the selective catalytic reduction of NO with NH3. The catalysts were characterized by means of XRD, N2 adsorption–desorption, TEM, XPS, UV–vis DRS, H2-TPR, NH3-TPD and EPR. Isolated Cu2+ ions are confirmed to be the catalytic active sites. Cu-4.42 catalyst exhibits high NO conversion (>80%) at the lowest temperature of 200 °C among all catalysts. It can be attributed to the maximum amount of isolated Cu2+ ions in Cu-4.42 catalyst. DFT calculations show that the isolated Cu ions are located in the pear shaped cavity and exhibit a preference for the neighboring of 6R planes of Cu–SAPO-18. NH3–SCR mechanism over Cu–SAPO-18 catalyst is elucidated by a combination of in situ DRIFTS technique and DFT calculations, in which the dissociation of NH3 and the oxidation of NO are shown to be key steps in the reaction.

The stable polymeric nitrogen and polynitrogen compounds have potential applications in high-energy-density materials. For beryllium nitrides, there is one known crystalline form, Be 3 N 2 , at ambient conditions. In the present study, the structural evolutionary behaviors of beryllium polynitrdes have been studied up to 100 GPa using first-principles calculations and unbiased structure searching method combined with density functional calculations. One stable structural stoichiometry of beyrllium polynitride has been theoretically predicted at high pressures. It may be experimentally synthesizable at high pressures less than 40 GPa. It is therefore possible to synthesize BeN 4 by compressing solid Be 3 N 2 and N 2 gas under high pressure and BeN 4 may be quenching recoverable to ambient conditions. The predicted high-pressure P2 1 /c-BeN 4 compound contains a novel variety of polynitrogen, extended polymeric 3D puckered N 10 rings network. To the best of our knowledge, this is the first time that stable N 10 rings network are predicted in alkaline-earth metal polynitrides. The decomposition of P2 1 /c-BeN 4 is expected to be highly exothermic, releasing an energy of approximately 6.35 kJ•g −1 . The present results open a new avenue to synthesize polynitrogen compound and provide a key perspective toward the understanding of novel chemical bonding in nitrogen-rich compounds. Results of the present study suggest that it is possible to obtain energetic polynitrogens in main-group nitrides under high pressure.

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