One-step synthesis of palladium/SBA-15 nanocomposites and its catalytic application

Green Synthesis of Oxide-Supported Pd Nanocatalysts by Laser Methods for Room-Temperature Carbon-Carbon Cross-Coupling Reactions

This work reports the design and development of a new class of highly active Pd nanocatalysts supported on substoichiometric oxides. These novel catalysts are generated by green laser synthesis methods to generate high-surface-area substoichiometric oxide nanoparticles followed by photoreduction in aqueous solutions to deposit highly active Pd nanocatalysts within the surface defects of the oxides. The laser methods eliminate the use of toxic chemicals, including hazardous solvents and chemical reducing agents, and allow efficient reduction of the Pd ions in aqueous solutions aided by the photogenerated electrons from the semiconductor support. The Pd catalysts incorporated within these oxides exhibit high activity for carbon-carbon bond-forming reactions. The Pd/TiO₂ catalyst with 0.3 mol % Pd achieves 100% conversion in the reaction between bromobenzene and benzeneboronic acid to the biphenyl product within 240 minutes at room temperature without any external heating. With a catalyst loading of 0.3 mol % Pd in the microwave-assisted reaction between bromobenzene and benzeneboronic acid at 60 °C, 92 and 83% conversions to the biphenyl product are achieved within 5 min of reaction time using the Pd/TiO₂ and Pd/ZnO catalysts, respectively. The results demonstrate a remarkable catalytic activity of the substoichiometric oxide-supported Pd catalysts with turnover frequencies (TOF, h^-1) of 24 000, 10 000, and 3200 achieved under mirowave-assisted reactions at 60 °C for the 0.03 mol% Pd of the Pd/TiO₂, Pd/ZnO, and Pd/ZrO₂ catalysts, respectively. The high activity and good reusability of these nanocatalysts are attributed to the optimum catalyst-support interaction between the small Pd nanoparticles and the surface defects of the substoichiometric oxide support prepared by the laser vaporization-controlled condensation method.

The fabrication of Au/Pd plasmonic alloys on UiO-66-NH2: an efficient visible light-induced photocatalyst towards the Suzuki Miyaura coupling reaction under ambient conditions

The current study on Au/Pd@UiO-66-NH₂ explores a novel approach towards photocatalytic SMC coupling reaction. This investigation highlights a well studied mechanistic pathway towards the formation of biphenyl as the target product.

Applications of SBA-15 supported Pd metal catalysts as nanoreactors in C-C coupling reactions

Nanoreactors are material structures with engineered internal cavities which create exclusive confined nanoscale surroundings for chemical reactions. The cavities of mesoporous silica SBA-15 can be used as nanoreactors for incorporating catalytic species such as metal nanoparticles, complexes etc. Since SBA-15 silica has a neutral framework, organic functional groups and heteroatoms have been embedded by direct or post-synthesis approaches in order to modify their functionality. Palladium is the most used transition metal for C-C bond formations. Because of the great importance of C-C coupling reactions, this review article aims at providing a deep insight into the state of art in the field of the synthesis and the application of mesoporous SBA-15 silica-supported Pd catalysts in C-C coupling transformations. In most cases, synthesis and modification of the catalyst, time and yield of reactions, recyclability and leaching of the Pd species from the SBA-15 support are discussed to reveal the role of SBA-15 in C-C coupling reactions.

Palladium Intercalated into the Walls of Mesoporous Silica as Robust and Regenerable Catalysts for Hydrodeoxygenation of Phenolic Compounds

Nanostructured noble-metal catalysts traditionally suffer from sintering under high operating temperatures, leading to durability issues and process limitations. The encapsulation of nanostructured catalysts to prevent loss of activity through thermal sintering, while maintaining accessibility of active sites, remains a great challenge in the catalysis community. Here, we report a robust and regenerable palladium-based catalyst, wherein palladium particles are intercalated into the three-dimensional framework of SBA-15-type mesoporous silica. The encapsulated Pd active sites remain catalytically active as demonstrated in high-temperature/pressure phenol hydrodeoxygenation reactions. The confinement of Pd particles in the walls of SBA-15 prevents particle sintering at high temperatures. Moreover, a partially deactivated catalyst containing intercalated particles is regenerated almost completely even after several reaction cycles. In contrast, Pd particles, which are not encapsulated within the SBA-15 framework, sinter and do not recover prior activity after a regeneration procedure.

Synthesis and characterization of bifunctional lipophilic and basic mesoporous organosilica supported palladium nanoparticles as an efficient and ecofriendly nanocomposite in aqueous Heck reaction

In the present study, a highly ordered mesoporous organosilica nanocomposite having modified pore channels with both lipophilic and basic units, SBA-R/Im-NH₂, was synthesized through surfactant-templated sol–gel methodology and post modification process.

Enhanced metal–support interactions between Pd NPs and ZrSBA-15 for efficient aerobic benzyl alcohol oxidation

Towards the aerobic oxidation of alcohols, palladium nanoparticle immobilized mesoporous catalysts have been extensively investigated; however, the preparation of efficient catalytic materials without using complexing moieties remains a challenge.

A novel route for the synthesis of alkanes from glycerol in a two step process using a Pd/SBA-15 catalyst

Glycerol is produced as a valuable by-product in the transesterification of fatty acids, but it cannot be used directly as a fuel additive.

Methyl oleate deoxygenation for production of diesel fuel aliphatic hydrocarbons over Pd/SBA-15 catalysts

Background

Catalytic deoxygenation is a prominent process for production of renewable fuels from vegetable oil. In this work, deoxygenation of technical grade methyl oleate to diesel fuel aliphatic hydrocarbons (C₁₅ – C₁₈) is evaluated with several parameters including temperature, hydrogen pressure and reaction time in a stirred batch reactor over Pd/SBA-15 catalysts.

Results

Two different SBA-15 morphologies i.e. spherelike and necklacelike structures have been synthesize as supports for Pd active metal. It is found that Pd dispersion on necklacelike SBA-15 is higher than that of spherelike SBA-15. Notably, higher Pd dispersion on necklacelike SBA-15 provides significant deoxygenation efficiency as compared to Pd/SBA-15-spherelike. Results show that H₂ pressures greatly determine the total ester conversion and selectivity to C₁₅ – C₁₈ aliphatic hydrocarbons. Total ester conversions with 55< selectivity to n-heptadecane are achieved using Pd/SBA-15-necklacelike at 270°C and 60 bar H₂ pressure within 6 h reaction time. Gas phase study reveals that formation of C₁₇ is generated via indirect decarbonylation when the reaction time is prolonged.

Conclusions

Pd/SBA-15-necklacelike catalyst exhibits good catalytic performance with high selectivity to diesellike aliphatic hydrocarbons (C₁₅ – C₁₈). The physicochemical properties of the Pd supported on different SBA-15 morphologies influence the deoxygenation activity of the catalysts. Furthermore, the reaction pathways are governed by the H₂ pressure as well as reaction duration.

Noble-metal-based catalysts supported on zeolites and macro-mesoporous metal oxide supports for the total oxidation of volatile organic compounds

The use of porous materials to eliminate volatile organic compounds (VOCs) has proven very effective towards achieving sustainability and environmental protection goals. The activity of zeolites and macro-mesoporous metal-oxide supports in the total oxidation of VOCs has been investigated, with and without noble-metal deposition, to develop highly active catalyst systems where the formation of by-products was minimal. The first catalysts employed were zeolites, which offered a good activity in the oxidation of VOCs, but were rapidly deactivated by coke deposition. The effects of the acido-basicity and ionic exchange of these zeolites showed that a higher basicity was related to exchanged ions with lower electronegativities, resulting in better catalytic performances in the elimination of VOCs. Following on from this work, noble metals were deposited onto macro-mesoporous metal-oxide supports to form mono and bimetallic catalysts. These were then tested in the oxidation of toluene to study their catalytic performance and their deactivation process. PdAu/TiO(2) and PdAu/TiO(2) -ZrO(2) 80/20 catalysts demonstrated the best activity and life span in the oxidation of toluene and propene and offered the lowest temperatures for a 50 % conversion of VOCs and the lowest coke content after catalytic testing. Different characterization techniques were employed to explain the changes occurring in catalyst structure during the oxidation of toluene and propene.