Jingxiang Zhao

Theoretical Investigation of the Interaction between Carbon Monoxide and Carbon Nanotubes with Single-Vacancy Defects

Density functional theory calculations are used to study the healing process of a defective CNT (i.e. (8,0) CNT) by CO molecules. The healing undergoes three evolutionary steps: 1) the chemisorption of the first CO molecule, 2) the incorporation of the C atom of CO into the CNT, accompanied by the adsorption of the leaving O atom on the CNT surface, 3) the removal of the adsorbed O atom from the CNT surface by a second CO molecule to form CO(2) and the perfect CNT. Overall, adsorption of the first CO reveals a barrier of 2.99 kcal mol(-1) and is strongly exothermal by 109.11 kcal mol(-1), while adsorption of a second CO has an intrinsic barrier of 32.37 kcal mol(-1)and is exothermal by 62.34 kcal mol(-1). In light of the unique conditions of CNT synthesis, that is, high temperatures in a closed container, the healing of the defective CNT could be effective in the presence of CO molecules. Therefore, we propose that among the available CNT synthesis procedures, the good performance of chemical vapor decomposition of CO on metal nanoparticles might be ascribed to the dual role of CO, that is, CO acts both as a carbon source and a defect healer. The present results are expected to help a deeper understanding of CNT growth.

High stability and superior catalytic reactivity of nitrogen-doped graphene supporting Pt nanoparticles as a catalyst for the oxygen reduction reaction: a density functional theory study

We investigated the structural and electronic properties of Pt13 nanoparticles on various nitrogen (N)-doped graphene and their interaction with O by density functional theory (DFT) calculations. The results revealed that the N-doping can greatly enhance the binding strength of Pt13 nanoparticles on the graphene surface, thus ensuring their high stability. For NC doping (N atoms directly substituting for C atoms), the enhanced binding strength of the Pt13 cluster is attributed to the activation of the carbon atoms around the N-dopant, while the strong hybridization of the d states of the Pt13 cluster with the sp2 dangling bonds of the N atoms in defective N-doped graphenes contributes to the strong adsorption. Moreover, a certain amount of electrons are transferred from Pt13 to the substrate accompanied by a substantial downshift of the Pt13 d-band center, thus greatly weakening the interaction of O on these composites: the adsorption energy of O is reduced from −3.700 eV on freestanding Pt13 nanoparticles to −1.762, −1.723, and −1.507 eV on deposited Pt13 ones on NC, 3NV, and 4ND structures, respectively. Hence, it is expected that N-doped graphene supported Pt nanoparticles exhibit super catalytic reactivity in the ORR.

CO oxidation catalyzed by silicon carbide (SiC) monolayer: A theoretical study.

Developing metal-free catalysts for CO oxidation has been a key scientific issue in solving the growing environmental problems caused by CO emission. In this work, the potential of the silicon carbide (SiC) monolayer as a metal-free catalyst for CO oxidation was systematically explored by means of density functional theory (DFT) computations. Our results revealed that CO oxidation reaction can easily proceed on SiC nanosheet, and a three-step mechanism was proposed: (1) the coadsorption of CO and O2 molecules, followed by (2) the formation of the first CO2 molecule, and (3) the recovery of catalyst by a second CO molecule. The last step is the rate-determining one of the whole catalytic reaction with the highest barrier of 0.65eV. Remarkably, larger curvature is found to have a negative effect on the catalytic performance of SiC nanosheet for CO oxidation. Therefore, our results suggested that flat SiC monolayer is a promising metal-free catalyst for CO oxidation.

Single transition metal atom embedded into a MoS2 nanosheet as a promising catalyst for electrochemical ammonia synthesis

The electrochemical reduction of N2 to NH3 (NRR) under ambient conditions is significant for sustainable agriculture. Here, by means of density functional theory (DFT) computations, the potential of a series of single transition metal (TM) atoms embedded into a MoS2 monolayer with an S-vacancy (TM/MoS2) as electrocatalysts for NRR was systematically investigated. Our DFT results revealed that among all these considered candidate catalysts, the single Mo atom embedded into the MoS2 nanosheet was found to be the most active catalyst for NRR with an onset potential of -0.53 V, in which the hydrogenation of the adsorbed N2* to N2H* is the potential-determining step. The high stabilization of the N2H* species is responsible for the superior performance of the embedded Mo atom for the NRR, which is well consistent with its d-band center. Our findings may facilitate the further design of single-atom electrocatalysts with high efficiency for NH3 synthesis at room temperature.

Two-dimensional iron–tetracyanoquinodimethane (Fe–TCNQ) monolayer: an efficient electrocatalyst for the oxygen reduction reaction

Searching for efficient, cheap, and stable non-Pt electrocatalysts for the oxygen reduction reaction (ORR) has been a major challenge for the development of fuel cells. Herein, we systematically investigated the potential of the experimentally synthesized two-dimensional (2D) metal–tetracyanoquinodimethane (M–TCNQ, where M denotes Mn, Fe, and Co) monolayers as novel ORR catalysts by means of density functional theory (DFT) computations. Our results revealed that O2 molecules can be chemisorbed and efficiently activated on the M–TCNQ monolayers, and the subsequent oxygen reduction can readily proceed via a 4e− pathway. Among the monolayers, the Fe–TCNQ monolayer exhibits the highest catalytic activity with onset potentials of 0.63 and −0.20 V in acidic and alkaline media, respectively. Remarkably, its electrocatalytic performance could be further enhanced by the attachment of axial halogen ligands. Therefore, the Fe–TCNQ monolayer might serve as a promising alternative to Pt-based catalysts for the ORR in fuel cells.

DFT-based study on the mechanisms of the oxygen reduction reaction on Co(acetylacetonate)2 supported by N-doped graphene nanoribbon

Development of low-cost and highly efficient electrocatalysts for oxygen reduction reaction (ORR) is still a great challenge for the large-scale application of fuel cells and metal–air batteries. In this work, by means of density functional theory (DFT) computations, we have systemically explored the anchoring of Co(acac)2 (acac = acetylacetonate) on N-doped graphene nanoribbon and its potential as the ORR electrocatalyst. Our DFT computations revealed that N-doped graphene nanoribbon can be used as the anchoring material of the Co(acac)2 complex due to the formation of a Co–O4–N moiety, thus ensuring its high stability. Especially, an O2 molecule can be moderately activated on the surface of the anchored Co(acac)2 complex, and the subsequent ORR steps prefer to proceed though a more efficient 4e pathway with a small overpotential (0.67 V). Therefore, the hybridization of Co(acac)2 with N-doped graphene can give rise to outstanding catalytic performance for ORR in fuel cells.

Nano metal oxides as efficient catalysts for selective synthesis of 1-methoxy-2-propanol from methanol and propylene oxide

Nano metal oxides such as Fe2O3, Fe3O4, CuO, NiO, ZnO and SnO2 were prepared and characterized using XRD, SEM and TEM analysis. These as-prepared metal oxide materials were used as catalysts for the etherification of methanol with propylene oxide (PO). The results showed that α-Fe2O3 exhibited outstanding catalytic performance with 97.7% conversion and 83.0% selectivity to MP-2 at 160 °C for 8 h. Furthermore, the relationship between the catalytic activity or selectivity and surface basicity or energy gap was investigated. This catalyst could be easily recovered and reused due to its heterogeneous catalytic nature.