Theoretical study on simultaneous removal of SO2, NO, and Hg0 over graphene: competitive adsorption and adsorption type change

Hydrogen cyanide catalytic hydrolysis mechanism by Al-doped graphene: A density functional theory study

CONTEXT

The hydrogen cyanide (HCN) hydrolysis reaction mechanism over Al-doped graphene was investigated through the density functional theory method. HCN preferentially adsorbed vertically on the Al top site to form a stable adsorption configuration. H2O preferentially adsorbed parallel on the Al top site to form a stable adsorption configuration. The competitive adsorption of HCN and H2O weakened the adsorption stability of each molecule over Al-doped graphene. The break of C-N and H-O bonds was the key process in the preferential fracture pathway of the C-H bond. The break of C-N and C-H bonds was the key process in the preferential fracture pathway of the H-O bond. HCN played the role of bridge in the joint adsorption process. H atom transfer and C-N bond cleavage promoted the generation of CO and NH3. The change in the order of H atom transfer determined the reaction energy barrier. NH2CHO was more likely to act as an intermediate to promote the hydrolysis process.

METHODS

The calculation work was achieved from the Dmol3 program in Material Studio 2017 using the GGA/PBE method with DNP basis, including the geometric structure and reaction pathway optimization, and adsorption energy calculation. All calculations were performed using a spin-polarized set and the TS method was used for DFT-D correction.

Experimental and theoretical studies on NO selective catalytic oxidation over α-MnO2

Based on the experimental and theoretical methods, the NO selective catalytic oxidation process was proposed. The experimental results indicated that lattice oxygen was the active site for NO oxide over the α-MnO₂(110) surface. In the theoretical study, DFT (density functional theory) and periodic slab modeling were performed on an α-MnO₂(110) surface, and two possible NO oxidation mechanisms over the surface were proposed. The non-defect α-MnO₂(110) surface showed the highest stability, and the surface O_s (the second layer oxygen atoms) position was the most active and stable site. O₂ molecule enhanced the joint adsorption process of two NO molecules. The reaction process, including O₂ dissociation and O=N-O-O-N=O formation, was calculated to carry out the NO catalytic oxidation mechanism over α-MnO₂(110). The results showed that NO oxidation over the α-MnO₂(110) surface exhibited the greatest possibility following the route of O=N-O-O-N=O formation. Meanwhile, the formation of O=N-O-O-N=O was the rate-determining step.