Theoretical Study on the O-H Fracture of Methanol on PtnCu4-n (n = 1, 2, 3) Catalysts with Different Coverages.

Direct methanol fuel cells (DMFCs) have attracted increasing attention as a very promising and important energy source. In this paper, density functional theory (DFT) is used to study the structure and O-H fracture mechanism of methanol adsorption on PtnCu4-n (111) (n = 1, 2, 3) binary metal catalyst surfaces under different coverages. By comparing the adsorption energy and dehydrogenation energy barriers of methanol, it is found that the adsorption strength and dehydrogenation energy barriers of methanol on Pt and Cu sites decreased with increasing coverage. At the same Pt and Cu ratio, methanol is more easily adsorbed on Cu sites. When Pt/Cu = 3:1 and 1:3, the PtCu binary catalyst has a significant impact on the energy barrier of breaking the O-H bond in methanol with the increase of coverage. Especially when Pt/Cu = 1:3 and the coverage is 1/4 ML, the energy barriers of O-H bond breaking in methanol on Pt and Cu sites are 0.63 and 0.61 eV, respectively, which are lower than that on pure Pt. It means that the Cu sites played a very important role in reducing the O-H fracture energy barrier of methanol. When Pt/Cu = 1:1, the change in the dehydrogenation energy barrier of methanol on Pt sites and Cu sites is not significant, indicating that the coverage has little effect on it.

The catalytic activity of PtnCum (n = 1-3, m = 0-2) clusters for methanol dehydrogenation to CO.

A large number of experiments show that PtCu catalyst has a good catalytic effect on methanol decomposition. Therefore, density functional theory (DFT) was used to further study the dehydrogenation of methanol catalyzed by PtnCum (n = 1-3, m = 0-2). The energy diagrams of O-adsorption path and H-adsorption path were drawn. By calculation, the Pt is the active site of the whole reaction process, and the barrier energy of the rate-determining step is 11.09 kcal mol-1 by Pt2Cu, which is lower than that of Pt3 and PtCu2. However, the complete dehydrogenation product of methanol, CO, is easier to dissociate from PtCu2 clusters than from Pt3 and Pt2Cu clusters. Therefore, Cu doping can improve the catalytic activity and anti-CO toxicity of Pt to a certain extent.

[Chemical constituents from Barringtonia racemosa].

To investigate the chemical constituents from Barringtonia racemosa, twelve compounds were isolated by chromatography methods and identified as 3ß-p-E-coumaroymaslinic acid (1), cis-careaborin (2), careaborin (3), maslinic acid (4), 2α, 3ß, 19α-trihydroxyolean-12-ene-24, 28-dioic acid (5), 3ß-p-Z-coumaroylcorosolic acid (6), corosolic acid (7), 1α, 2α, 3ß, 19α-tetrahydroxyurs-12-en-28-oic acid (8), 19α-hydroxyl ursolic acid (9), 3α, 19α-dihydroxyurs-12-en-24, 28-dioic acid (10), tormentic acid (11), 3-hydroxy-7, 22-dien-ergosterol（12） by the NMR and MS data analysis. Among them, compounds 1-4,7-12 were obtained from the genus Barringtonia for the first time. All the compounds didn't show nocytotoxic activity against MCF-7 and A549 cell lines (IC50>50 mg•L⁻¹).