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For di-nitroaromatics hydrogenation, it is a challenge to achieve the multi-step hydrogenation with high activity and selectivity due to the complexity of the process involving two nitro groups. Consequently, many precious metal catalysts suffer from low activity for this multi-step hydrogenation reaction. Herein, we employ a fully exposed Pt clusters catalyst consisting of an average of four Pt atoms on nanodiamond@graphene (Ptn/ND@G), demonstrating excellent catalytic performance for the multi-step hydrogenation of 2,4-dinitrotoluene. The TOF (40647 h−1) of Ptn/ND@G is significantly superior to that of single Pt atoms catalyst, Pt nanoparticles catalyst, and even all the known catalysts. Density functional theory calculations and absorption experiments reveal that the synergetic interaction between the multiple active sites of Ptn/ND@G facilitate the co-adsorption/activation of reactants and H2, as well as the desorption of intermediates/products, which is the key for the higher catalytic activity than single Pt atoms catalyst and Pt nanoparticles catalyst. Hydrogenating di-nitroaromatics with high activity and selectivity is challenging due to the process's complexity. Here the authors present a fully exposed Pt clusters catalyst for 2,4-dinitrotoluene hydrogenation, suggesting that the synergy between multiple active sites and moderate adsorption behavior is crucial for the high catalytic activity. [ABSTRACT FROM AUTHOR]

Single-site pincer-ligated iridium complexes exhibit the ability for C-H activation in homogeneous catalysis. However, instability and difficulty in catalyst recycling are inherent disadvantages of the homogeneous catalyst, limiting its development. Here, we report an atomically dispersed Ir catalyst as the bridge between homogeneous and heterogeneous catalysis, which displays an outstanding catalytic performance for n-butane dehydrogenation, with a remarkable n-butane reaction rate (8.8 mol·gIr−1·h−1) and high butene selectivity (95.6%) at low temperature (450 °C). Significantly, we correlate the BDH activity with the Ir species from nanoscale to sub-nanoscale, to reveal the nature of structure-dependence of catalyst. Moreover, we compare Ir single atoms with Pt single atoms and Pd single atoms for in-depth understanding the nature of metal-dependence at the atomic level. From experimental and theoretical calculations results, the isolated Ir site is suitable for both reactant adsorption/activation and product desorption. Its remarkable dehydrogenation capacity and moderate adsorption behavior are the key to the outstanding catalytic activity and selectivity. Single-site pincer-ligated iridium complexes exhibit the ability for C-H activation but suffer from instability and difficulty in catalyst recycling. Here the authors design an atomically dispersed Ir catalyst which can be considered the bridge between homogeneous and heterogeneous catalysis and displays an outstanding catalytic performance in n-butane dehydrogenation. [ABSTRACT FROM AUTHOR]

In recent years, the accident rate of urban rail transit PPP (public–private partnerships) project under construction has been relatively high, and the issue of security risks has attracted great attention from all walks of life. Therefore, it is necessary to identify, analyze, and evaluate the issue of security risks of the urban rail transit PPP project. This paper takes the PPP project of urban rail transit as the object. Through offline interviews and surveys and online questionnaires, this paper focuses on identifying and analyzing the risks brought by the introduction of PPP mode to the urban rail transit project and its action mechanism. The risk evaluation method based on Bayesian network model is studied, which is described from three dimensions: risk occurrence probability, risk reasoning, and risk sensitivity. Finally, an example of Xuzhou Metro Line 3 is given to verify the feasibility of the proposed method. This study provides a reference basis for relevant practitioners and promotes the healthy development of the industry. [ABSTRACT FROM AUTHOR]