Ruthenium and palladium bimetallic nanoparticles achieving functional parity with a rhodium cocatalyst for TiO2-photocatalyzed ring hydrogenation of benzoic acid

Our previous study showed that a rhodium (Rh) cocatalyst is indispensable for ring hydrogenation of benzoic acid over a titanium(IV) oxide (TiO2) photocatalyst. In this study, we explored ring hydrogenation under an Rh-free condition by using two kinds of cocatalyst that were inactive for this reaction when used solely. Cyclohexanecarboxylic acid as the ring hydrogenation product was successfully obtained when ruthenium (Ru) and palladium (Pd) were simultaneously loaded on TiO2, indicating that this bimetallic system can be used in place of an Rh cocatalyst in ring hydrogenation. The state and distribution of Ru and Pd in particles loaded on TiO2 were investigated by transmission electron microscopy, X-ray photon spectroscopy, and X-ray absorption near edge structure analysis. The functions of Ru and Pd as cocatalysts are discussed on the basis of results of characterization and activity tests. The effects of different contents of Ru and Pd in Ru-Pd/TiO2 prepared by a two-step photodeposition method on catalytic activity and the features of the reaction system were investigated in detail.

CO Oxidation at Near-Ambient Temperatures over TiO2-Supported Pd-Cu Catalysts: Promoting Effect of Pd-Cu Nanointerface and TiO2 Morphology

Significant improvement of the catalytic activity of palladium-based catalysts toward carbon monoxide (CO) oxidation reaction has been achieved through alloying and using different support materials. This work demonstrates the promoting effects of the nanointerface and the morphological features of the support on the CO oxidation reaction using a Pd-Cu/TiO2 catalyst. Pd-Cu catalysts supported on TiO2 were synthesized with wet chemical approaches and their catalytic activities for CO oxidation reaction were evaluated. The physicochemical properties of the prepared catalysts were studied using standard characterization tools including SEM, EDX, XRD, XPS, and Raman. The effects of the nanointerface between Pd and Cu and the morphology of the TiO2 support were investigated using three different-shaped TiO2 nanoparticles, namely spheres, nanotubes, and nanowires. The Pd catalysts that are modified through nanointerfacing with Cu and supported on TiO2 nanowires demonstrated the highest CO oxidation rates, reaching 100% CO conversion at temperature regime down to near-ambient temperatures of ~45 °C, compared to 70 °C and 150 °C in the case of pure Pd and pure Cu counterpart catalysts on the same support, respectively. The optimized Pd-Cu/TiO2 nanowires nanostructured system could serve as efficient and durable catalyst for CO oxidation at near-ambient temperature.

Synthesis and characterization of supported stabilized palladium nanoparticles for selective hydrogenation in water at low temperature

Zirconia supported vacant phosphotungstate stabilized Pd nanoparticles (Pd-PW11/ZrO2) were prepared using a simple impregnation and post reduction method, characterized and their efficiency for selective C[double bond, length as m-dash]C hydrogenation of unsaturated compounds explored. The establishment of a hydrogenation strategy at low temperature using water as solvent under mild conditions makes the present system environmentally benign and green. The catalyst shows outstanding activity (96% conversion) with just a small amount of Pd(0) (0.0034 mol%) with high substrate/catalyst ratio (29 177/1), TON (28 010) and TOF (14 005 h-1) for cyclohexene (as a model substrate) hydrogenation. The catalyst was recovered by simple centrifugation and reused for up to five catalytic cycles without alteration in its activity. The present catalyst was found to be viable towards different substrates with excellent activity and TON (18 000 to 28 800). A study on the effect of addenda atom shows that the efficiency of the catalyst can be enhanced greatly by increasing the number of counter protons. This challenging strategy would greatly benefit sustainable development in chemistry as it diminishes the use of organic solvents and offers economic and environmental benefits as water is cheap and non-toxic.

Hydrogen- and noble metal-free conversion of nitro aromatics to amino aromatics having reducible groups over an organically modified TiO2 photocatalyst under visible light irradiation

A TiO₂ modified with 2,3-dihydroxynaphthalene responds to visible light, and electrons are photogenerated to the CB of TiO₂ under light irradiation in the presence of a suitable hole scavenger.

Preparation of a magnetic mesoporous Fe3O4–Pd@TiO2 photocatalyst for the efficient selective reduction of aromatic cyanides

Fe₃O₄–Pd@TiO₂ exhibited extremely superior photocatalytic activity for the selective reduction of aromatic cyanides to aromatic primary amines.

Mediated electrochemical synthesis of metal nanoparticles

The review integrates and analyzes data of original studies on the mediated electrosynthesis of metal nanoparticles — a new efficient and environmentally attractive process for obtaining these particles in the solution bulk. The general principles and specific features of electrosynthesis of metal nanoparticles by mediated electroreduction of metal ions and complexes are considered. The discussed issues include the role of cyclic voltammetry in the development of this method, the method efficiency, some aspects of selection of mediators, and aggregation, stabilization and catalytic activity of the metal nanoparticles thus obtained. Analysis of the results of mediated electrosynthesis of Pd, Ag, PdAg, Au, Pt and Cu nanoparticles stabilized by various compounds and mediated electrogeneration of highly active metal particles is used as basic data for discussion.

The bibliography includes 247 references.

Titanium(iv) oxide having a copper co-catalyst: a new type of semihydrogenation photocatalyst working efficiently at an elevated temperature under hydrogen-free and poison-free conditions

A copper-loaded titanium(iv) oxide photocatalyst exhibited perfect selectivity in hydrogenation of alkynes to alkenes in an alcohol solution at 298 K under hydrogen-free and poison-free conditions. A slight elevation in the reaction temperature to 323 K greatly increased the reaction rate with the selectivity being preserved and the formation of an H2 by-product being suppressed. The apparent activation energy of 4-octyne semihydrogenation was determined to be 54 kJ mol-1, indicating that the rate determining step of this photocatalytic reaction was not an electron production process but a thermocatalytic hydrogenation process under light irradiation.

Visible-light-driven Efficient Photocatalytic Reduction of Organic Azides to Amines over CdS Sheet-rGO Nanocomposite

CdS sheet-rGO nanocomposite as a heterogeneous photocatalyst enables visible-light-induced photocatalytic reduction of aromatic, heteroaromatic, aliphatic and sulfonyl azides to the corresponding amines using hydrazine hydrate as a reductant. The reaction shows excellent conversion and chemoselectivity towards the formation of the amine without self-photoactivated azo compounds. In the adopted strategy, CdS not only accelerates the formation of nitrene through photoactivation of azide but also enhances the decomposition of azide to a certain extent, which entirely suppressed formation of the azo compound. The developed CdS sheet-rGO nanocomposite catalyst is very active, providing excellent results under irradiation with a 40 W simple household CFL lamp.

Photocatalytic chemoselective cleavage of C–O bonds under hydrogen gas- and acid-free conditions

In the presence of a palladium-loaded TiO₂ photocatalyst, the cleavage of benzyl phenyl ether derivatives afforded toluenes and phenols simultaneously.

Ring hydrogenation of aromatic compounds in aqueous suspensions of an Rh-loaded TiO2 photocatalyst without use of H2 gas

Aromatics with a carboxyl group were almost quantitatively hydrogenated to corresponding cyclohexanes over an Rh–TiO₂ photocatalyst under H₂-free conditions.

Visible light-induced heterogeneous Meerwein–Ponndorf–Verley-type reduction of an aldehyde group over an organically modified titanium dioxide photocatalyst

An organically modified TiO₂ photocatalyst chemoselectively converted benzaldehydes to the corresponding benzyl alcohols under visible light irradiation.

Photocatalytic hydrogenation of furan to tetrahydrofuran in alcoholic suspensions of metal-loaded titanium(iv) oxide without addition of hydrogen gas

Furan was almost quantitatively hydrogenated to tetrahydrofuran in methanolic suspension of a Pd-TiO₂ photocatalyst with an apparent quantum efficiency of 37%.

Organically modified titania having a metal catalyst: a new type of liquid-phase hydrogen-transfer photocatalyst working under visible light irradiation and H2-free conditions

Organically modified titania having a metal catalyst (OMTC), 2,3-dihydroxynaphthalene-modified titania having palladium metal, successfully worked as a hydrogen-transfer (C[double bond, length as m-dash]C hydrogenation) photocatalyst in the presence of triethanolamine as the hydrogen source under visible light irradiation and hydrogen-free conditions.

A facile synthesis of a solvent-dispersible magnetically recoverable Pd0 catalyst for the C–C coupling reaction

A Pd⁰/Fe₃O₄-DA/DMG catalyst exhibited excellent catalytic activity toward the Suzuki, Heck and Kumada cross coupling reaction with a high yield. It is an especially efficient catalyst for Suzuki and Heck coupling in water.

Using the hydrogen and oxygen in water directly for hydrogenation reactions and glucose oxidation by photocatalysis

This work reports the utilization of hydrogen in water for the hydrogenation of organic compounds and the oxygen for the oxidation of glucose simultaneously by photocatalysis.

Direct utilization of the abundant hydrogen and oxygen in water for organic reactions is very attractive and challenging in chemistry. Herein, we report the first work on the utilization of the hydrogen in water for the hydrogenation of various organic compounds to form valuable chemicals and the oxygen for the oxidation of glucose, simultaneously by photocatalysis. It was discovered that various unsaturated compounds could be efficiently hydrogenated with high conversion and selectivity by the hydrogen from water splitting and glucose reforming over Pd/TiO₂ under UV irradiation (350 nm). At the same time, glucose was oxidated by the hydroxyl radicals from water splitting and the holes caused by UV irradiation to form biomass-derived chemicals, such as arabinose, erythrose, formic acid, and hydroxyacetic acid. Thus, the hydrogen and oxygen were used ideally. This work presents a new and sustainable strategy for hydrogenation and biomass conversion by using the hydrogen and oxygen in water.

Light-driven integration of the reduction of nitrobenzene to aniline and the transformation of glycerol into valuable chemicals in water

This work reports the efficient integration of the conversion of nitrobenzene to aniline and the transformation of glycerol to valuable chemicals driven by UV-light over Pd/TiO₂ in water.

Photocatalytic hydrogenation of alkenes to alkanes in alcoholic suspensions of palladium-loaded titanium(iv) oxide without the use of hydrogen gas

Styrene was successfully hydrogenated to ethylbenzene in alcoholic suspensions of a Pd–TiO₂ photocatalyst.