Structure-Controlled Chemical Properties of PdZn Near-Surface Alloys

Abstract

PdZn catalysts have demonstrated high potential in methanol steam reforming, water–gas shift reaction, and propane dehydrogenation. In order to understand the reaction mechanisms, β1-PdZn surface alloys were produced on Pd(111) and Pd(100) single crystal substrates via vapor deposition of diethylzinc. The structural properties and thermal stability of the surface alloys were investigated by X-ray photoelectron spectroscopy, low-energy electron diffraction, and scanning tunneling microscopy (STM) techniques. Several phases of the PdZn alloy were observed on the Pd(111) surface depending on the preparation conditions. On Pd(111), atomically resolved STM images show a transition from a PdZn p(2 × 1) rowlike structure to the β1-PdZn­(111) surface to a zigzaglike structure when annealed at increasingly higher temperatures. Similarly, a transition from the β1-PdZn­(001) to the β1-PdZn­(010) structure was observed when PdZn alloys were prepared on a Pd(100) single crystal. The adsorption of carbon monoxide and propylene was investigated by high-resolution electron energy loss spectroscopy. CO was found to bind exclusively in the linear position (no bridge configuration) for the β1-PdZn­(010) surface, while complete destabilization of CO was observed on all other β1 alloy surfaces. Propylene was found to no longer adsorb on any of the β1 alloy surfaces even at subambient temperatures, 130 K. To complement the experimental observation, DFT calculations have been performed, which point to lower binding energies of CO and propylene on PdZn surfaces compared to Pd surfaces. This fundamental surface science study depicts the inability of propylene to adsorb on the 1:1 alloy terrace surfaces, thereby leading to the inhibition of deeper dehydrogenation, hydrogenolysis, and coke formation. Hence, this can be considered as one of the major factors for the high alkene selectivity and stability of PdZn alloy catalysts for alkane dehydrogenation.

Approach to Low Contact Resistance Formation on Buried Interface in Oxide Thin-Film Transistors: Utilization of Palladium-Mediated Hydrogen Pathway

“…Notable enhancement for Zn 0 compared to In 0 and Ga 0 is attributed to the facile reaction between Pd and ZnO during the annealing treatment, as evidenced by the X-ray diffraction (XRD) pattern (Figure S1). The peak shift of Pd 111 diffraction indicates the formation of intermetallic PdZn x after the annealing process, ,, which is also one of the reasons for the formation of the highly conductive interfacial layer. Hence, the formation of the highly conductive interfacial layer is attributed to the metallization resulting from hydrogen interacting with oxygen in a-IGZO at the interface, accompanied by the formation of an intermetallic phase between Pd and Zn, which eliminates the Schottky barrier and reduces the contact resistance between the metal and a-IGZO.…”