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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]

This paper is based on the proximity engineering project of the Baishiyi tunnel group passing under the Chongqing West Station track group. Considering the train load and the spatial relationship of the tunnel and track groups, the settlement patterns, horizontal displacement, and differential settlement of the tunnel–strata–tracks system during the excavation process are studied through theoretical calculations and numerical simulation methods. The results indicate that the tunnel vault, strata, and track settlement deformation patterns are similar. Throughout the tunnel construction process, the tracks underwent uplift, settlement, and eventually stabilized. The settlement trough formed by the excavation of the three tunnels below the track group has an impact range of 25–145 m. Between 35 and 75 m, the differential settlement of the double track gradually increases with excavation. As the tunnel face reaches 75 m, the track differential settlement gradually converges and tends to stabilize. To minimize the impact of underpass tunnel construction on track groups, it is recommended to use a combination of full-section hole grouting and surface reinforcement grouting for ground reinforcement. Additionally, optimizing the construction parameters, including the step length and primary support closure time, and strengthening the locking anchor can further reduce the impact. [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]

To solve the problem of freezing damage in cold-region tunnels, this study proposed a rubber airbag interlayered composite lining system, and tested its performance of buffering, pressure adjustment, waterproofing, and heat preservation by simulating a low-temperature environment in an artificial freezing chamber. The experiment results show that the frost-heaving force exerted on the lining can always be lower than 1.69 kPa by constantly adjusting the airbag pressure, and the maximum frost-heaving force can reach 28.25 kPa without the airbag. In addition, the airbag also has good waterproof performance. Finally, the airbag can significantly improve the temperature field of the surrounding rock and reduce the freezing depth (6.75 cm < 17.25 cm). The insulation effect of the airbag is positively correlated with its thickness and negatively correlated with the thermal conductivity of the filling gas. The insulation effect of CO2 is better than that of air. The rubber airbag interlayered composite lining system provides a new scheme for freezing damage control in cold-region tunnels. [ABSTRACT FROM AUTHOR]

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]

In order to reduce the noble metal palladium dosage in the preparation of CL-20 so as to reduce its production cost, several carbon supports were prepared successfully using the hydrothermal carbonization method in the absence or presence of urea using microcrystalline cellulose (MC) as the carbon source, and the corresponding Pd(OH)2/C catalysts were fabricated using the deposition–precipitation method, which showed high activity in the debenzylation reaction of hexabenzylhexaazaisowurtzitane (HBIW) and tetraacetyldibenzylhexaazaisowurtzitane (TADB). It was found that all the catalysts showed a high efficiency in the debenzylation of HBIW, indicating that the structure of the used carbon supports had a limited impact on the catalyst performance in this reaction. On the contrary, the activities of the catalysts in the debenzylation of TADB were quite different. The results of the nitrogen sorption isotherm measurement (BET), scanning electron microscope (SEM), scanning transmission electron microscopy (STEM), powder X-ray diffraction (XRD), element analysis and temperature programmed desorption (TPD), as well as X-ray photoelectron spectra (XPS) characterizations of the supports and catalysts, showed that the relatively high activity of Pd/HTC in the debenzylation of TADB was related to the high Pd dispersion and novel mesoporous structure, while the further higher activity and stability of Pd/HTC-N1:1 in the same reaction were related with its high Pd dispersion, high total oxidized Pd species, and high surface pyridinic N contents as well as the eggshell distribution of Pd species on the support. [ABSTRACT FROM AUTHOR]

In order to solve the large deformation problem of Shanenshan No.2 Tunnel of the China-Lao's Railway, the design principle of the support resistant limiting damper (SRLD) was introduced, and the energy-consuming support scheme with the SRLD was designed according to the field working conditions from the point of rational utilization of the load-bearing capacity behind the peak of the surrounding rock. Based on the comprehensive analysis of the working state, structural deformation and internal force monitoring results of the primary support of the test section, the rationality of using the SRLD to treat the tunnel with carbonaceous SLATE stratum was verified. The results showed that after tunnel excavation, the system energy was dissipated mainly through the plastic strain energy of surrounding rock, while the energy dissipated by support was limited. Therefore, if the plastic deformation ability of surrounding rock could be fully utilized and the energy could be dissipated by surrounding rock itself, the energy conservation and conversion could be accomplished, thus reducing the pressure of surrounding rock. The SRLD was a pressure yielding control system, suitable for small eccentric pressure environments controlled by deformation pressure, which assised the surrounding rock to dissipate energy in an elastic-plastic state under reduced surrounding rock pressure, without damage. The SRLD was successfully applied in the double-lane section of Shannon Hill Tunnel No. 2, which significantly reduced the pressure on the surrounding rock compared to the "strong support and hard roof", and avoided problems such as cracking of the initial support and buckling of the steel frame without strengthening the initial support parameters, thus improving the economy of the project while ensuring safety. [ABSTRACT FROM AUTHOR]

Developing a catalyst with high SO2 and H2O resistance to achieve high-performance CO oxidation for specific industrial applications is highly desirable. Here, three catalysts were prepared using cerium titanium composite oxide (CeTi), molybdophosphate with Keggin structure-modified CeTi (Keg-CeTi), and molybdophosphate without Keggin structure-modified CeTi (MoP-CeTi) as supports, and their sulfur and water resistance in CO oxidation were tested. The characterization of XRD, BET, SO2/H2O-DRIFTS, XPS, TEM, SEM, NH3/SO2-TPD, H2-TPR, and ICP techniques revealed that the high SO2 and H2O resistance of Pt/Keg-CeTi in CO oxidation was related to its stronger surface acidity, better reduction of surface cerium and molybdenum species, and lower SO2 adsorption and transformation compared to Pt/CeTi and Pt/MoP-CeTi. [ABSTRACT FROM AUTHOR]