Hongyang Liu

Interface-Confined Ferrous Centers for Catalytic Oxidation

Catalysis at the Edge Many catalysts in solution, such as metalloenzymes and homogeneous metal complexes, create active sites where the metal ion is available to bind and activate reactants. Such coordinately unsaturated ferrous sites, or CUFs, have been created in a supported heterogeneous catalyst by Fu et al. (p. 1141). Ferrous oxide islands grown on platinum single-crystal surfaces were much more reactive for CO oxidation at low temperatures than more oxidized ferric islands. This difference arose from sites at the interface between the islands and the Pt surface that activated oxygen. Silica-supported Pt-Fe catalysts were active for CO removal from hydrogen streams, a reaction critical for maintaining the activity of fuel cells. The interface between ferrous oxide islands and a platinum support contains sites that activate dioxygen for catalytic reactions. Coordinatively unsaturated ferrous (CUF) sites confined in nanosized matrices are active centers in a wide range of enzyme and homogeneous catalytic reactions. Preparation of the analogous active sites at supported catalysts is of great importance in heterogeneous catalysis but remains a challenge. On the basis of surface science measurements and density functional calculations, we show that the interface confinement effect can be used to stabilize the CUF sites by taking advantage of strong adhesion between ferrous oxides and metal substrates. The interface-confined CUF sites together with the metal supports are active for dioxygen activation, producing reactive dissociated oxygen atoms. We show that the structural ensemble was highly efficient for carbon monoxide oxidation at low temperature under typical operating conditions of a proton-exchange membrane fuel cell.

Highly active mesostructured silica hosted silver catalysts for CO oxidation using the one-pot synthesis approach

A facile one-pot approach gave isolated silver nanoparticles anchored on a mesostructured silica matrix in a self-assembled way; these gave 100% CO conversion in CO oxidation at room temperature, which is higher than or comparable to the conversion obtained using noble metal catalysts.

Reversible Structural Modulation of Fe–Pt Bimetallic Surfaces and Its Effect on Reactivity

Tunable surface: The surface structure of the Fe-Pt bimetallic catalyst can be reversibly modulated between the iron-oxide-rich Pt surface and the Pt-skin structure with subsurface Fe via alternating reduction and oxidation treatments (see figure). The regenerated active Pt-skin structure is active in reactions involving CO and/or O.

Reversible structural transformation of FeOx nanostructures on Pt under cycling redox conditions and its effect on oxidation catalysis

Understanding dynamic changes of catalytically active nanostructures under reaction conditions is a pivotal challenge in catalysis research, which has been extensively addressed in metal nanoparticles but is less explored in supported oxide nanocatalysts. Here, structural changes of iron oxide (FeO(x)) nanostructures supported on Pt in a gaseous environment were examined by scanning tunneling microscopy, ambient pressure X-ray photoelectron spectroscopy, and in situ X-ray absorption spectroscopy using both model systems and real catalysts. O-Fe (FeO) bilayer nanostructures can be stabilized on Pt surfaces in reductive environments such as vacuum conditions and H2-rich reaction gas, which are highly active for low temperature CO oxidation. In contrast, exposure to H2-free oxidative gases produces a less active O-Fe-O (FeO2) trilayer structure. Reversible transformation between the FeO bilayer and FeO2 trilayer structures can be achieved under alternating reduction and oxidation conditions, leading to oscillation in the catalytic oxidation performance.

Reconstruction of Rh nanoparticles in methanol oxidation reaction

We have developed a new method based on both kinetic and thermodynamic control to tune the dimensions of Rh nanocubes (varied from 2 nm to 6 nm) and obtained Rh concaves (>10 nm). The prepared Rh nanocubes were loaded on SiO2 as catalysts for the partial oxidation of methanol. Our results showed that the reaction has an induction period, and the catalyst activity changes with the time on stream, implying the possible change in active sites of the catalysts. A number of characterization methods were used to systematically investigate the catalysts before and after the reaction. It is concluded that the reconstruction of the catalyst surface occurred under reaction atmosphere and the increase in catalytic performance was due to the formation of highly active crystal planes and sites. Our results indicate that facet transformation exists in heterogeneous catalysis reactions, which accounts for some unexpected activity evolution during the reaction.

Combined single-pass conversion of methane via oxidative coupling and dehydroaromatization: a combination of La2O3/BaO and Mo/HZSM-5 catalysts

Abstract Combined single-pass conversion of CH4 via oxidative coupling and dehydroaromatization over La 2 O 3 /BaO and 6Mo/HZSM-5 catalyst system was evaluated. The improvement in the stability is mainly attributed to the high activities of the Mo carbide species in the gasification of cokes and reverse Boudouard reactions.