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The activation process is a key step in preparing porous carbon. Herein, three kinds of green activators were separately used to successfully prepare N-doped porous carbons through a two-step strategy: hydrothermal carbonization and chemical activation using microcrystalline cellulose as the carbon source and urea as the nitrogen source. Palladium was deposited on these N-doped microcrystalline cellulose-based carbons (NMC-X, where X represents the activator) via a traditional deposition–precipitation method, and the resulting Pd nanoparticle catalysts (Pd/NMC-X) showed high activity in the selective hydrogenation of quinoline under mild conditions, particularly Pd/NMC-ZC (ZC, zinc carbonate), which achieved complete conversion of quinoline within 100 min at 40 °C and 4 atm H2. Characterization results suggest that the high activity of Pd/NMC-ZC is mainly attributed to the special electronic structure of its Pd species, particularly the distribution of valence states and reducibility of Pd and the high hydrogen spillover capacity between Pd and NMC-ZC. The chemical activation by ZC leads to the formation of multiple defect sites on the carbon skeleton, modifying the carbon surface properties to enhance hydrogen spillover. This also provides an excellent environment for Pd nanoparticle anchoring, thus increasing the Pd-support interactions and regulating the electronic structure of Pd. [ABSTRACT FROM AUTHOR]

Palladium-catalyzed Suzuki–Miyaura cross-coupling reaction is a powerful route to construct carbon–carbon bonds in fine-chemical synthesis. However, the activation of relatively chemically inert aryl chlorides under mild conditions in this reaction is still a great challenge. Herein, N-doped hollow carbon nanosheet assemblies (HCNAs) were first developed by hydrothermal carbonization of glucose through an in situ self-generating template method, and the corresponding Pd single-atom catalyst (Pd1/HCNAs) fabricated by a conventional deposition–precipitation method showed superior catalytic activity (TOFs = 499 h–1) and high stability for the Suzuki coupling reaction of chlorobenzene under mild condition. Characterizations of transmission electron microscopy, electron paramagnetic resonance spectroscopy, Raman spectra, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy showed that the high catalytic activity and stability of Pd1/HCNAs were related with its full positively charged Pd single-atom active sites and the low reducibility of Pd atom due to the strong interaction between Pd atom and the HCNA carrier. Meanwhile, the relative high chlorobenzene and phenylboric acid adsorption and the low affinity to product biphenyl as well as the special three-dimensional structure of Pd1/HCNAs were also beneficial to improve the catalytic activity. [ABSTRACT FROM AUTHOR]

Given the shortcomings of the tunnel overbreak and underbreak control and primary support sectional area detection such as the single means, large workload, low efficiency, and poor accuracy, the use of three-dimensional laser technology can solve the above problems. Based on the Badaling Tunnel Great Wall underground station of the Beijing-Zhangjiakou Railway, the 3D laser scanning technology is used to analyze the distribution of the tunnel overbreak and underbreak and the sectional area of the primary support, compared with the total station measurement results. The results showed that the layout of the scanning measurement station should consider the requirements of scanning accuracy, control the station length and scanning incidence angle, and minimize the scanning station length to reduce the scanning error. The majority of the tunnel section was in overbreak, with the overbreak area ranging from 6.22 m2 to 13.17 m2and the overbreak rate ranging from 0.283 to 0.598, and the area of underbreak was relatively small; no overexceeded headroom was found in the primary support, and the tunnel vault was not overbreak. The primary support clearance value of the vault is 0∼15 mm, the clearance value of the sidewall is 35 mm∼40 mm, and the sidewall needs to be secondary shotcrete. The difference value between the 3D laser scanning measurement data and the total station measurement data is within 3 mm, which is within the error range, indicating the validity and reliability of the 3D laser measurement result.

Large deformations can easily occur when tunneling through weak surrounding rock with high underground stresses. Under high-stress environments, the surrounding rock stores a large amount of strain energy, and the strain energy stored in the soft and weak surrounding rock enclosure is dissipated through the large traveling plastic deformation. Therefore, the effective use of the surrounding rock's bearing capacity and energy dissipation is a feasible solution to the large deformation problem. Based on the energy principle, this study designs a high compressibility, large stroke energy-dissipation element, which transforms the traditional support into energy-dissipation support and solves the problem of large deformation by reasonably utilizing the "displacement" of the surrounding rock. The experimental results showed that the steel plate assembled structure had an initial peak value of about 15 MPa, a constant resistance of about 2 MPa with a large stroke, and a compression rate of more than 75%, with good post-compression flexural peak characteristics. Elastic–plastic buckling analyses of defective steel plate composite structures were carried out using finite element analysis software, and the deformation and force characteristics of a variety of steel plate composite structures after buckling under actual field conditions were investigated. Based on the 3D laser scanning system, the thickness of the upper and lower steel plates of the steel plate composite structure was set to 1 cm, the height of the vertical plate was set to 28 cm, and the thickness was set to 8 mm. The original rigid supporting method was converted into one of compression support by circumferentially embedding the steel plate composite structure into the initial support structure. The resulting support configuration offered a high safety factor because the pressure of the surrounding rock was released by the deformation of the steel plate composite structure. [ABSTRACT FROM AUTHOR]