Efficient Ceria–Platinum Inverse Catalyst for Partial Oxidation of Methanol

Abstract

Ceria-platinum-based bilayered thin films deposited by magnetron sputtering were developed and tested in regard to their catalytic activity for methanol oxidation by employing a temperature-programmed reaction (TPR) technique. The composition and structure of the samples were characterized by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Both conventional (oxide-supported metal nanoparticles [NPs]) and inverse configurations (metal with oxide overlayer) were analyzed to uncover the structural dependence of activity and selectivity of these catalysts with respect to different pathways of methanol oxidation. We clearly demonstrate that the amount of cerium oxide (ceria) loading has a profound influence on methanol oxidation reaction characteristics. Adding a noncontinuous adlayer of ceria greatly enhances the catalytic performance of platinum (Pt) in favor of partial oxidation of methanol (POM), gaining an order of magnitude in the absolute yield of hydrogen. Moreover, the undesired by-production of carbon monoxide (CO) is strongly suppressed, making the ceria-platinum inverse catalyst a great candidate for clean hydrogen production. It is suggested that the methanol oxidation process is facilitated by the synergistic effect between both components of the inverse catalyst (involving oxygen from ceria and providing a reaction site on the adjacent Pt surface) as well as by the fact that the ability of ceria to exchange oxygen (i.e., to alter the oxidation state of Ce between 3+ and 4+) during the reaction is inversely proportional to its thickness. The increased redox capability of the discontinuous ceria adlayer shifts the preferred reaction pathway from dehydrogenation of hydroxymethyl intermediate to CO in favor of its oxidation to formate.

Ceria-based model catalysts: fundamental studies on the importance of the metal–ceria interface in CO oxidation, the water–gas shift, CO2hydrogenation, and methane and alcohol reforming

“…Reaction of methanol with oxygen can lead to the selective formation of formaldehyde 28 or the production of molecular hydrogen and carbon dioxide (CH 3 OH + 1/2O 2 → 2H 2 + CO 2 ). 99 Vanadia supported on ceria shows a remarkable activity for selective oxidation reactions. 100,101 The selective oxidation of methanol to formaldehyde was studied on a well-defined VO x /CeO 2 (111) model system for which the atomic surface structure has been determined.…”

“…Temperature-programmed desorption at low vanadia loadings revealed reactivity at much lower temperature (310-430 K in Figure 18) as compared to pure ceria and vanadia on inert supports such as silica. 99 Calculations based on Density functional theory indicate that the special structural and electronic properties of VO 2 units dispersed on ceria facilitate the dehydrogenation of methanol (Figure 18). 99 At the origin of this support effect is the ability of ceria to stabilize reduced states by accommodating electrons in localized f-states.…”

“…99 Calculations based on Density functional theory indicate that the special structural and electronic properties of VO 2 units dispersed on ceria facilitate the dehydrogenation of methanol (Figure 18). 99 At the origin of this support effect is the ability of ceria to stabilize reduced states by accommodating electrons in localized f-states. 99 Catalysts with a CeO x /Pt configuration exhibit high activity for the production of hydrogen through the partial oxidation of methanol.…”

“…99 At the origin of this support effect is the ability of ceria to stabilize reduced states by accommodating electrons in localized f-states. 99 Catalysts with a CeO x /Pt configuration exhibit high activity for the production of hydrogen through the partial oxidation of methanol. 99 Adding a non-continuous adlayer of ceria greatly enhances the catalytic performance of Pt gaining an order of magnitude in the yield of hydrogen.…”

2D oxides on metal materials: concepts, status, and perspectives

“…Another example of efficient inverse-catalyst system is offered by Pt-supported ceria, investigated as catalyst for methanol oxidation for clean hydrogen production. Ostroverkh et al 147 have shown that the performances of pure Pt surfaces are greatly enhanced when an ad-layer of ceria is adsorbed, ascribing the catalytic efficiency at the interface to the synergic contribution of the oxide in exchanging oxygen and of the metallic in anchoring the reactant species. Ceria on Ag particles has been proposed as a CO oxidation catalyst 148 , a system that exhibits also SERS resonant properties two orders of magnitude more pronounced than bare Ag particles.…”