Performance enhancement in the water–gas shift reaction of platinum deposited over a cerium-modified TiO2 support

On the stability of hydroxyl groups on substituted titania

The present study reports the stability of hydroxyl groups involving the surface coordinated oxygens of Pd,C,N-doped, and Pd/C and Pd/N-codoped anatase TiO₂, probed using DFT calculations.

Needle ball-like nanostructured mixed Cu-Ni-Co oxides: Synthesis, characterization and application to the selective oxidation of sulfides to sulfoxides

A mixed nano-metal oxides of Cu-Ni-Co has been synthesized. Several characterization techniques (EDS, XRD, TEM, and SEM) have been used to provide insight into the nature and structure of the catalyst. The size of this mixed metal oxide is 22 nm. The SEM images indicate that the sample with spherical particles, of which spherical assembly is comprised of elongated rod/needle-like subunits pointing radially outward, creates a needle ball-like structure. To efficiently catalyze the selective oxidation of sulfide towards sulfoxide, this heterogeneous catalyst uses an oxidizing agent (hydrogen peroxide- H₂O₂) and a solvent (acetonitrile) in mild conditions. The influence of reaction temperature and sulfide/oxidant molar ratio was evaluated with respect to sulfide conversion and chemoselectivity towards the sulfoxide product. Under optimized conditions, product yields in the range from 70 to 97% were obtained.

Recent advances of titanium dioxide (TiO2) for green organic synthesis

This review focuses on the recent development of TiO₂ as a catalyst in green organic synthesis including in hydrodeoxygenation, hydrogenation, esterification/transesterification, the water–gas shift reaction, and visible light-induced organic transformation.

Structure and special chemical reactivity of interface-stabilized cerium oxide nanolayers on TiO2(110)

Novel interface-stabilized ceria nanophases have been grown on TiO2(110) by physical vapor deposition. At low coverage, dumbbell nanostructures constituted by reconstructed titania and ceria clusters are formed, while long range ordered nanoxides can be obtained by increasing the ceria dose. Scanning tunneling microscopy and photoemission spectroscopy were used to characterize the electronic properties of the films, showing that the TiO2 substrate can effectively stabilize ceria in reduced form over a wide range of experimental conditions. Epitaxial coupling is a very useful tool for tuning the chemical properties of mixed oxide systems. The special electronic properties of the films have a direct counterpart in the chemical activity, which has been investigated by temperature programmed desorption using methanol as a probe molecule. The experimental results indicate an exceptional activity of the ceria-titania interface in the selective dehydration of methanol to formaldehyde at an unprecedented low temperature (330 K).

Complete oxidation of formaldehyde at ambient temperature over supported Pt/Fe2O3 catalysts prepared by colloid-deposition method

The catalytic properties of iron oxide supported platinum catalysts (Pt/Fe(2)O(3)), prepared by a colloid deposition route, were investigated for the complete oxidation of formaldehyde. It is found that all the Pt/Fe(2)O(3) catalysts calcined at different temperatures (200-500°C) were active for the oxidation of formaldehyde. Among them, the catalysts calcined at lower temperatures (i.e., 200 and 300°C) exhibited relatively high catalytic activity and stability, which could completely oxidize HCHO even at room temperature. Based on a variety of physical-chemical characterization results, it is proposed that the presence of suitable interaction between Pt particles and iron oxide supports, which is mainly in the form of Pt-O-Fe bonds, should play a positive role in determining the catalytic activity and stability of the supported Pt/Fe(2)O(3) catalysts.

High catalytic activity of Au/CeOx/TiO2(110) controlled by the nature of the mixed-metal oxide at the nanometer level

Mixed-metal oxides play a very important role in many areas of chemistry, physics, materials science, and geochemistry. Recently, there has been a strong interest in understanding phenomena associated with the deposition of oxide nanoparticles on the surface of a second (host) oxide. Here, scanning tunneling microscopy, photoemission, and density-functional calculations are used to study the behavior of ceria nanoparticles deposited on a TiO(2)(110) surface. The titania substrate imposes nontypical coordination modes on the ceria nanoparticles. In the CeO(x)/TiO(2)(110) systems, the Ce cations adopt an structural geometry and an oxidation state (+3) that are quite different from those seen in bulk ceria or for ceria nanoparticles deposited on metal substrates. The increase in the stability of the Ce(3+) oxidation state leads to an enhancement in the chemical and catalytic activity of the ceria nanoparticles. The codeposition of ceria and gold nanoparticles on a TiO(2)(110) substrate generates catalysts with an extremely high activity for the production of hydrogen through the water-gas shift reaction (H(2)O + CO --> H(2) + CO(2)) or for the oxidation of carbon monoxide (2CO + O(2) --> 2CO(2)). The enhanced stability of the Ce(3+) state is an example of structural promotion in catalysis described here on the atomic level. The exploration of mixed-metal oxides at the nanometer level may open avenues for optimizing catalysts through stabilization of unconventional surface structures with special chemical activity.