Unsupported Nanoporous Gold Catalyst Research Articles

Photocatalytic Dehydrative Etherification of Alcohols by an Unsupported Nanoporous Gold Catalyst

Key words photocatalysis - gold catalysis - etherification - alcohols - ethers

Unsupported nanoporous gold catalyst for highly selective hydroamination of alkynes.

An efficient and highly selective heterogeneous catalyst system for hydroamination of alkynes was developed using unsupported gold nanopores (AuNPore) for the first time. The AuNPore-catalyzed highly regioselective hydroamination of alkynes proceeded smoothly without any additive and solvent under mild conditions (rt-50 °C) to yield Markovnikov imines in satisfactory to excellent yields. No gold leached from AuNPore during the hydroamination of alkynes. Moreover, the catalyst was easily recovered and reused without any loss of catalytic activity. A one-pot, two-step procedure using a single AuNPore catalyst has been devised to produce secondary amines derived from readily available alkynes and anilines with high atom efficiency.

Heterogeneous Catalytic Reduction of Tertiary Amides with Hydrosilanes Using Unsupported Nanoporous Gold Catalyst

AbstractWe have demonstrated that the unsupported nanoporous gold (AuNPore) was a green and highly efficient heterogeneous catalyst for the reduction of amides to amines using hydrosilanes as reductants. A variety of tertiary amides with a broad functional groups were reduced to the corresponding tertiary amines in the presence of 2 mol% of AuNPore and PheMe2SiH or (Me2SiH)2O under mild conditions. AuNPore catalyst was recovered by simple filtration and used for twelve times without any loss of catalytic activity. The AuNPore/hydrosilane system was also successfully applied to the hydrosilative reduction of sulfoxides and N‐oxides.magnified image

Unsupported Nanoporous Gold Catalyst for Chemoselective Hydrogenation Reactions under Low Pressure: Effect of Residual Silver on the Reaction

For the first time, H-H dissociation on an unsupported nanoporous gold (AuNPore) surface is reported for chemoselective hydrogenation of C≡C, C═C, C═N, and C═O bonds under mild conditions (8 atm H2 pressure, 90 °C). Silver doping in AuNPore, which was inevitable for its preparation through a process of dealloying of Au-Ag alloy, exhibited a remarkable difference in catalytic activity between two catalysts, Au>99Ag1NPore and Au90Ag10NPore.The former was more active and the latter less active in H2 hydrogenation, while the reverse tendency was observed for O2 oxidation. This marked contrast between H2 reduction and O2 oxidation is discussed. Further, Au>99Ag1NPore showed a high chemoselectivity toward reduction of terminal alkynes in the presence of internal alkynes which was not achieved using supported gold nanoparticle catalysts and other previously known methods. Reductive amination, which has great significance in synthesis of amines due to its atom-economical nature, was also realized using Au>99Ag1NPore, and the Au>99Ag1NPore/H2 system showed a preference for the reduction of aldehydes in the presence of imines. In addition to this high chemoselectivity, easy recovery and high reusability of AuNPore make it a promising heterogeneous catalyst for hydrogenation reactions.

Low-temperature CO oxidation over unsupported nanoporous gold catalysts with active or inert oxide residues

Nanoporous gold (NPG) catalysts with different types of oxide residues are fabricated by a simple electrochemical dealloying method with the aim of exploring the origin of high catalytic activity on unsupported gold catalyst systems. By leaching out the reactive components from AuCu and AuAl alloys, unsupported NPG with so-called active CuO and inert Al2O3 residues were generated, characterized by an open interconnected network architecture with a narrow ligament size distribution. The NPG catalyst with inert Al2O3 residues shows a CO reaction rate and turnover frequency similar to those on NPG with active CuO residues under the same measurement conditions. In comparison, NPG(Cu) with active CuO residues exhibits better catalytic durability for CO oxidation than NPG(Al) catalyst, possibly because of its stabilization for nanoporous architecture. Experimental observations suggest that the so-called active or inert oxide residues in the as-made NPG catalysts have almost no effect on the intrinsic catalytic activity of gold, whereas metallic gold plays the catalytic role in this unsupported NPG system.

Methyl ester synthesis catalyzed by nanoporous gold: from 10−9 Torr to 1 atm

Highly selective synthesis of methyl esters can be achieved by oxidative coupling of methanol and aldehydes (acetaldehyde, butyraldehyde) under mild conditions using unsupported nanoporous gold catalysts over a wide pressure range (from 10−9 Torr to 1 atm).

Oxidative Coupling of Alcohols and Amines over Bimetallic Unsupported Nanoporous Gold: Tailored Activity through Mechanistic Predictability

AbstractAn unsupported nanoporous gold catalyst is employed for the direct coupling of primary alcohols and amines to the corresponding amides in the liquid phase. Among others, the reaction of methanol and dimethylamine to the industrially relevant dimethylformamide proceeds smoothly at 40 °C (turnover frequency≈40 h−1). The activation of molecular oxygen is identified as a key parameter. Doping of the unsupported catalyst by an admetal (Ru, Ag) is used to increase the activity of the catalyst considerably for this reaction (turnover frequency≈100 h−1).

Chemoselective reduction of α,β-unsaturated aldehydes using an unsupported nanoporous gold catalyst.

The remarkable effect of an unsupported nanoporous gold catalyst (AuNPore) on chemoselective hydrogenation of α,β-unsaturated aldehydes using silane has been described. Enals can be reduced with excellent selectivity, giving the corresponding allylic alcohols in good to high chemical yields.

ChemInform Abstract: From Model Studies on Au(111) to Working Conditions with Unsupported Nanoporous Gold Catalysts: Oxygen‐Assisted Coupling Reactions

AbstractReview: 82 refs.

ChemInform Abstract: Unsupported Nanoporous Gold Catalyst for Highly Selective Hydrogenation of Quinolines.

AbstractFor the first time, the highly efficient and regioselective hydrogenation of selected quinoline derivatives to 1,2,3,4‐tetrahydroquinolines using unsupported nanoporous gold as catalyst and organosilane with water as a hydrogen source is reported.

From model studies on Au(1 1 1) to working conditions with unsupported nanoporous gold catalysts: Oxygen-assisted coupling reactions

The fundamental principles derived from model studies on metallic gold single crystals for oxygen-assisted reactions provides a framework for understanding nanoporous gold–silver alloy catalysts under working catalytic conditions (ambient pressure, moderate temperature). The mechanistic principles for reactivity obtained from fundamental studies guide the understanding of reactivity and selectivity for oxygen-assisted self-coupling and cross-coupling reactions of alcohols on the catalytic materials. Furthermore, current results coupled with recent reports regarding the activation of nanoporous gold provide insight into the activation/deactivation of these catalysts and the challenge of maintaining sustainable reactivity. Finally, new fabrication methods and developments for gold-based nanoporous alloys with Cu, Pd, and Pt show that complementary reactivity and new properties are possible through these materials.

Unsupported Nanoporous Gold Catalyst for Highly Selective Hydrogenation of Quinolines

For the first time, the highly efficient and regioselective hydrogenation of quinoline derivatives to 1,2,3,4-tetrahydroquinolines using unsupported nanoporous gold (AuNPore) as a catalyst and organosilane with water as a hydrogen source is reported. The AuNPore catalyst can be readily recovered and reused without any loss of catalytic activity.

Oxygen‐Mediated Coupling of Alcohols over Nanoporous Gold Catalysts at Ambient Pressures

Unsupported catalyst for green chemistry: The aerobic oxidation and coupling of primary alcohols (methanol, ethanol, n-butanol) to give the corresponding aldehydes and esters at temperatures below 100 °C is facilitated by unsupported nanoporous gold catalysts. The experimental conditions employed allow a close comparison to model experiments and open the door to a molecular-level understanding of the reaction.

Research on unsupported nanoporous gold catalyst for CO oxidation

Nanoporous gold (NPG), a novel unsupported gold catalyst prepared by dealloying, exhibits exceptional catalytic activity for CO oxidation. Systematic studies were carried out on this new catalytic system, including the active sites of catalysts, the reaction kinetics, and activity dependence as functions of space velocity and temperature. Our results show strong evidence that metallic gold atoms on NPG are the intrinsic active sites at which the reaction of CO with O 2 occurs. The kinetic study found that the reaction rate of CO oxidation on unsupported NPG depends significantly on CO concentration but only slightly on O 2 concentration. We suggest that CO adsorption plays a decisive role in CO oxidation on NPG as the rate-limiting step. By completely ruling out the support influence, our findings provide considerable insight into the role of gold catalysts.