DFT Investigation of the Adsorption/dissociation Mechanisms of Methyl Nitrite on the Pd(111) Surface

The adsorption behavior of methyl nitrite （MN） on the closed-packed Pd（111） sur- face has been investigated in detail by using density functional theory （DFT）. MN binds to the surface in two alternative forms, using the nitrogen atom attached to the surface. An overall net charge transfer from the substrate to the cis-MN molecule is also confirmed. In addition, the reaction mechanism for the dissociation of MN on the Pd（111） surface has been identified and compared with the methanol decomposition via O-H scission. The results demonstrate that MN is a more active reactant than methanol for the oxidative addition to the Pd catalyst. The possible reason has been analyzed from the adsorption behaviors and reaction barriers, that is, MN is chemically absorbed on the Pd（111） surface; the CHaO-NO bond scission, leading to the formation of adsorbed methoxy species, is much more favorable than that of the O-H bond scission and has a large exothermic behavior.

Research on thermal risk and decomposition behavior of methyl nitrite

The thermal hazards of methyl nitrite(MN)were investigated in the present study.The determination and evaluation of MN decomposition were conducted using a C600 micro thermometer.The thermal runaway reaction characteristics of the compound under different initial pressures were obtained using a VSP2 calorimeter.The kinetic parameters of MN were obtained by regression fitting and calculation of the microthermal experimental data.The experimental and calculated results demonstrated that the potential explosion risk of MN is very high.In addition,there was a high energy barrier in the early stage of the uncontrolled decomposition of MN;however,once the decomposition reaction was initiated,the subsequent decomposition was easily conducted.Under the conditions of adiabatic simulation,the possibility that the reaction was uncontrolled increases with the initial temperature and pressure of the system,and there is a great potential safety risk.

Paired-Pd(Ⅱ) centers embedded in HKUST-1 framework: Tuning the selectivity from dimethyl carbonate to dimethyl oxalate

CO oxidative coupling to dimethyl oxalate(DMO) is the most crucial step in coal to ethylene glycol. Pdbased supported catalysts have been verified effective for generating DMO, but concomitant generation of dimethyl carbonate(DMC) is always unavoidable. It is generally accepted that Pd(0) is the active species for producing DMO, while Pd(II) for DMC. However, density functional theory calculations have proposed that the selectivity to DMO or DMC highly depends on the space state of Pd species rather than its oxidative state. It is thus urgently desired to develop high-efficient catalysts with well-defined structure,and further to elucidate the structure-performance relationship. In this work, HKUST-1 with unique structure of paired-Cu(Ⅱ) centers was chosen as ideal support to construct the catalysts with respective paired-Pd(Ⅱ) centers and isolated-Pd(Ⅱ) centers via in situ Pd species doping. In despite of featuring Pdδ+(δ≈2) oxidation state, the synthesized paired-Pd(Ⅱ)/HKUST-1 catalyst still exhibited DMO as dominant product(90.8% of DMO selectivity). For isolated-Pd(Ⅱ)/HKUST-1 catalyst, however, the main product was DMC(84.8% of DMC selectivity). Based on catalyst characterizations, the structures of paired-Pd(Ⅱ) centers and isolated-Pd(Ⅱ) centers were determined. DMO was generated from the coupling of adjacent *COOCH;intermediates adsorbed on paired-Pd(Ⅱ) centers, while DMC was produced from the reaction between methyl nitrite and the *COOCH;intermediates formed on isolated-Pd(Ⅱ) centers. Current work is the first MOFs-based catalyst with well-defined structure being applied in CO oxidative coupling reaction, which not only sheds light on the structure-performance relationship, but also inspires the potential of using MOFs as tunable platform to design high-efficient catalysts in heterogeneous catalysis.

Influence of crystalline phase of Li-AI-O oxides on the activity of Wacker-type catalysts in dimethyl carbonate synthesis

The catalysts supported on LiA1508 （spinel） for vapor phase synthesis of dimethyl carbonate （DMC） from methyl nitrite （MN） have been studied. Their catalytic activities on supports prepared by different methods were evaluated in a continuous reactor. The samples were characterized by powder X-ray diffraction, N2 adsorption-desorption isotherms, fourier transform infrared spectroscopy and temperature-programmed reduction of H2. Li/A1 molar ratio and calcination temperature greatly influence the structure of crystalline phase of Li-AI-O oxides. Desirable LiAIsO8 （spinel） was formed at 800℃, while LiA1508 （primitive cube） formed at 900℃ is undesirable for the reaction. A high Li/A1 molar ratio, which was related with LiA102, also slowed the reaction rate. The electron transfer ability and the interaction with active component are the important properties of the spinel-based supports. The CuC12-PdC12/LiAIsO8 （spinel） with better electron transfer ability and low Pd2＋ reduction temperature exhibited a better catalytic ability.