Surface chemistry of titanium vanadium carbide: Tailoring interfacial reactivity of carbides

The fundamental surface chemistry of single crystal mixed metal carbide Ti0.35V0.65C with respect to tailoring interfacial reactivity and the understanding of its frictional properties is presented. The electronic properties of Ti0.35V0.65C (100) were compared to its parent carbides, TiC (100) and VC (100). A combined treatment of the core level and valence band X-ray phototelectron spectroscopy (XPS), supported by density functional theory (DFT), has shown that the addition of vanadium atoms into the matrix of TiC modifies the nature of the d band of the carbide. The electronic character of the mixed carbide was determined to be intermediate to that of TiC and VC.;To understand the influence of electronic character on chemical reactivity of this carbide, adsorption studies of different relevant molecules were performed. The reaction of CO with the mixed carbide produced molecular adsorption at cryogenic temperatures; the interaction on the mixed carbide was stronger than TiC but less than that of VC. It was demonstrated that the d orbital population of the carbide is responsible for the greater pi-backbonding of CO on VC as compared to Ti0.35V0.65C and TiC. The catalytic properties of the mixed carbide were also explored through temperature programmed desorption (TPD) studies of cyclohexene on Ti0.35V 0.65C (100). The reaction selectively produces benzene with ∼35% reactivity. Ethanol and neopentyl acetate desorption studies on Ti0.35 V0.65C (100) were also investigated. For both molecules, the mixed carbide demonstrated activity toward the cleavage of O-H and C-O bonds. The TPD of ethanol produced a mixture of multilayer, molecular and dissociative desorption, leading to the formation of ethene. The TPD of neopentyl acetate produced the desorption of neopentyl alcohol as well as other small fragments. The extent of surface reactivities of both molecules on the mixed carbide was found to be intermediate to that of TiC and VC. This was attributed to the intermediate electronic character of the mixed carbide with respect to the two monocarbides.;The relative frictional properties of the TiC (100), VC (100) and Ti 0.35V0.65C (100) under organic medium have also been explored using atomic force microscopy (AFM). Comparative friction-load plots indicated a trend for the relative friction coefficients, TiC (100) < Ti0.35 V0.65C (100) < VC (100), linked to the surface free energy differences of the carbide surfaces.