自组装型Pt/γ-Al2O3催化剂用于低温去除挥发性有机物

分别通过自组装法(AS)和浸渍法(WI)制备得到纳米催化剂Pt/γ-Al₂O₃-AS和Pt/γ-Al₂O₃-WI, 并用于评价甲苯、异丙醇、丙酮、乙酸乙酯等易挥发性有机物(VOCs)的氧化性能. 通过各种表征手段探究了催化剂形态、结构及表面性质与催化剂氧化活性的关系. 结果表明, Pt/γ-Al₂O₃-AS在低温下即可实现VOCs的完全氧化. 在气体浓度(体积分数)为1000×10^-6, 空速为18000 mL·g^-1·h^-1的条件下, 甲苯、异丙醇、丙酮、乙酸乙酯被Pt/γ-Al₂O₃-AS催化剂完全氧化的温度分别为130、135、145、215℃, 展现出了优异的氧化性能, 且具有很好的稳定性. 该催化剂较高的比表面积、较小的Pt纳米粒径、较好的Pt纳米颗粒分散度、更好的低温还原效果及丰富的表面羟基是具有较高催化活性的重要因素.     

Equivalent formulations of ＂the equation of life＂

Motivated by progress in theoretical biology a recent proposal on a general and quantitative dynamical framework for nonequilibrium processes and dynamics of complex systems is briefly reviewed. It is nothing but the evolutionary process discovered by Charles Darwin and Alfred Wallace. Such general and structured dynamics may be tentatively named "the equation of life". Three equivalent formulations are discussed, and it is also pointed out that such a quantitative dynamical framework leads naturally to the powerful Boltzmann–Gibbs distribution and the second law in physics. In this way, the equation of life provides a logically consistent foundation for thermodynamics. This view clarifies a particular outstanding problem and further suggests a unifying principle for physics and biology.     

组合型Pt/TiO_2催化剂用于低温催化甲苯完全氧化

将均匀分布的纳米Pt粒子直接吸附到TiO2载体上,即制得了组合型Pt/TiO2催化剂(Pt/TiO2-AS).与浸渍法制备的Pt/TiO2催化剂(Pt/TiO2-WI)比较,Pt/TiO2-AS催化剂在催化甲苯完全氧化反应中表现出了很好的催化性能,甲苯转化率为100%时的反应温度低至150°C,而且即使在较高甲苯浓度和较高气体空速下,该催化剂也能保持较好的催化性能.通过X射线衍射(XRD)、N2吸附-脱附(BET)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)、氢气程序升温还原(H2-TPR)及傅里叶变换红外(FTIR)光谱等对两种Pt/TiO2催化剂的结构和表面性能进行了表征.结果表明组合型Pt/TiO2-AS催化剂粒径小(2.5 nm),活性组分主要以Pt0形式存在且分布在载体表面,而且载体表面Ti―O键活化使催化剂具有较强的催化氧化能力.另外,活性中心的价态变化(Pt0→Ptδ+)是导致Pt/TiO2-AS催化剂失活的主要原因.     

Lyapunov function as potential function： A dynamical equivalence

For a physical system, regardless of time reversal symmetry, a potential function serves also as a Lyapunov function, providing convergence and stability information. In this paper, the converse is constructively proved that any dynamics with a Lyapunov function has a corresponding physical realization: a friction force, a Lorentz force, and a potential function. Such construction establishes a set of equations with physical meaning for Lyapunov function and suggests new approaches on the significant unsolved problem namely to construct Lyapunov functions for general nonlinear systems. In addition, a connection is found that the Lyapunov equation is a reduced form of a generalized Einstein relation for linear systems, revealing further insights of the construction.     

Stochastic Gradient Descent and Anomaly of Variance-Flatness Relation in Artificial Neural Networks

Stochastic gradient descent(SGD), a widely used algorithm in deep-learning neural networks, has attracted continuing research interests for the theoretical principles behind its success. A recent work reported an anomaly(inverse) relation between the variance of neural weights and the landscape flatness of the loss function driven under SGD [Feng Y and Tu Y Proc. Natl. Acad. Sci. USA 118 e2015617118(2021)]. To investigate this seeming violation of statistical physics principle, the properties of...