Silica-supported Pd Catalysts Research Articles

Synergistic effects of La loading on furfural hydrogenation using wrinkled silica-supported Pd catalysts: Role of partially oxidized Pd and base sites

The catalytic hydrogenation of furfural (FF) to tetrahydrofurfuryl alcohol (THFAL) is complicated by competing hydrogenation reactions involving the carbonyl group and furan ring. To address this challenge, we developed Pd/xLa@wrinkled silica (Pd/xLa@KCC) catalysts exhibiting excellent efficiency via the optimization of La/Si molar ratios, improved Pd dispersion, and stabilization of partially oxidized Pd particles (Pdδ+). These catalysts were designed for the selective hydrogenation of FF to THFAL. Pd/0.2La@KCC, characterized by a high level of oxygen defects, good basicity, and abundant Pdδ+ species, achieved complete conversion and 91.2 % THFAL selectivity at 45 °C within 6 h. Pd/0.2La@KCC exhibited a THFAL formation rate of 100.9 mmol/g/h, 10.8 times higher than that of Pd/0.02La@KCC. Improved Pd dispersion increased the available metallic surface area for H2 dissociations, whereas abundant Lewis-base sites and Pdδ+ species served as adsorption sites for the carbonyl group and furan ring, respectively. The catalyst facilitated the activation and conversion of the furan ring and carbonyl group to THFAL owing to the parallel adsorption geometry of FF. This approach highlights the importance of the surface characteristics of the catalyst for achieving exceptional selectivity and efficiency. Our findings provide valuable insights into the development of advanced catalysts exhibiting excellent selectivity for biomass-derived chemicals.

Spectroscopic determination of metal redox and segregation effects during CO and CO/NO oxidation over silica-supported Pd and PdCu catalysts

We report the effects of alloying Cu into silica supported Pd nanoparticles on the catalytic activity, surface composition, and particle structure during CO oxidation Pd is highly active for CO oxidation but is inhibited by relevant competitive reagents (e.g. NO) at low temperatures (< 150 °C). By alloying Cu into Pd nanoparticles, NO inhibition is suppressed without any CO oxidation activity loss. Infrared spectroscopy illustrates the formation of surface nitrosyl (NO-Pd) is eliminated in the PdCu alloy catalyst, preventing CO oxidation inhibition by NO. X-ray absorption spectroscopy studies show that Pd in the monometallic catalyst forms a surface oxide after light-off. Conversely, in the PdCu catalyst, Pd remains metallic during reaction, independent of temperature, whereas the Cu oxidizes when the catalyst becomes active, after light-off. Furthermore, DRIFTS studies show that the Cu segregates to the surface as the catalyst becomes active for diesel oxidation, presumably becoming the O2 adsorption site.

Morphology-dependent wrinkled silica-supported Pd catalysts for hydrogenation of furfural under mild conditions

The production of tetrahydrofurfuryl alcohol (THFAL) from biomass-derived furfural (FF) via one-pot hydrogenation is challenging owing to the high hydrogen pressure and temperature requirements of the system. In this study, a hydrothermal method is used to synthesize a series of wrinkled silica (KCC-1) supports having different morphologies and textural properties by modulating the cetylpyridinium bromide hydrate (CPB)/tetraethyl orthosilicate (TEOS) ratio. Subsequently, Pd-supported KCC-1 catalysts are fabricated along with a Pd/SiO2 catalyst (for comparative studies) via a chemical reduction method. Interestingly, the morphological features of the supports, such as the specific surface area, pore size, and Pd anchoring sites, differed significantly for different CPB/TEOS ratios. Among the synthesized catalysts, Pd/KCC 0.3, with the lowest proportion of Pd nanoparticles deposited on the external porous surface, exhibits the highest catalytic activity, owing to its large specific surface area and moderate pore size. Moreover, it shows the highest FF conversion of 100% and THFAL selectivity of 85% in 6 h at 50 °C under 20 bar H2.

Hydrogen-controlled structural reconstruction of palladium-bismuth oxide cluster to single atom alloy for low-temperature CO oxidation

Palladium (Pd) has been widely regarded as a high-performance catalyst for various oxidative reactions, however, the actual structure of active site remains controversial due to structural evolution under operation conditions. Herein, we prepared a series of bismuth (Bi)-doped silica-supported Pd catalysts and found a hydrogen-controlled structural reconstruction mechanism of palladium-bismuth oxide cluster to single atom alloy to efficiently catalyze low-temperature CO oxidation. The formation of PdxBiyOz clusters with unique Pd−O−Bi coordination structure could enhance the sinter-resistance ability of Pd species. This structural evolution of active site is clearly uncovered by in-situ XAFS results, in which metallic Bi−Pd shell gradually generates as the increase of reduction temperature without any metallic Bi−Bi bond. More importantly, PdBi1 single atom alloy exhibits a good CO oxidation activity with a CO2 production rate of 413 μmolCO2·gPd−1·s−1 at 100 °C and excellent catalytic stability. Density function calculation (DFT) results indicate that there are geometric and electronic effects between Bi and Pd atoms, which favor total linear-CO adsorption, activate CO and O2 molecules, and reduce the barrier for the formation of OO-CO intermediates in PdBi1 single atom alloy.

Low temperature green methanol synthesis by CO2 hydrogenation over Pd/SiO2 catalysts in slurry reactor

The utilization of the greenhouse gas of carbon dioxide (CO2) for fuel and value-added chemicals synthesis has become globally indispensable process for healthy environment. In this context, the hydrogenation of CO2 to methanol is an attractive avenue for achieving such goal. Thus, we prepared mesoporous silica-supported nanocrystalline palladium metal (Pd) for methanol synthesis by CO2 hydrogenation. To investigate the role of Pd metal, the synthesized mesoporous silica was loaded with 1, 2, 3 and 4 wt% of Pd. Physicochemical profile of synthesized mesoporous silica supported Pd catalysts were assessed by Inductively coupled plasma - optical emission spectrometry (ICP-OES), X-ray diffraction (XRD), Field-Emission Scanning Electron Microscopy (FESEM), Nitrogen adsorption–desorption and Temperature Program Reduction (TPR) techniques. ICP-OES measurement confirmed the actual Pd metal loading on the mesoporous silica support. XRD confirmed amorphous and crystalline nature of mesoporous silica and Pd metal, respectively. FESEM images exhibited homogenous and well dispersed Pd metal particles on the surface of mesoporuse silica support. Nitrogen adsorption desorption studies displayed enlargement in BET surface area with Pd promotion. Reduction behaviour of PdO was revealed by TPR data over the studied temperature range. The structure–activity studies suggested the degree of Pd crystallinity and higher dispersions as amongst the main factors contributing to the performance of Pd/SiO2 catalysts for pure CO2 hydrogenation in slurry reactor.

Selective Oxidation of Glyoxal to Glyoxalic Acid by Air over Mesoporous Silica Supported Pd Catalysts

A series of mesoporous silica (KIT-6, MCM-41 and SBA-15) supported Pd catalysts were successfully synthesized and applied for selective oxidation of glyoxal. All of these catalysts exhibited significantly higher activity than commercial Pd/C. Among them, Pd/KIT-6 exhibited the best activity and selectivity with 41.3% glyoxal conversion and 57.0% selectivity to glyoxalic acid. The better performance of Pd/KIT-6 was attributed to its three-dimensional mesoporous structure. The three-dimensional mesoporous structure of KIT-6 could enhance Pd dispersion, providing sufficient accessible active sites which improved the conversion of glyoxal. Meanwhile, the better mass transfer capability of Pd/KIT-6 allowed glyoxalic acid to leave the catalyst easily, reducing the probability of over-oxidation. The ratio of kI (rate constant of initial oxidation reaction) to kII (rate constant of over-oxidation) was compared among three catalysts. The kI/kII of Pd/KIT-6 (0.50) was higher than that of Pd/MCM-41 (0.39) and Pd/SBA-15 (0.34), which reflected its best selectivity from kinetic aspect.

Effect of the amine group content on catalytic activity and stability of mesoporous silica supported Pd catalysts for additive-free formic acid dehydrogenation at room temperature

A strong metal-support interaction (SMSI) between amine-functionalized silica supports and Pd nanoparticles is one of important factors to determine the catalytic activity of additive-free formic acid dehydrogenation at room temperature over Pd/NH2-silica catalysts. However, there are few reports on the effect of the content of amine functional groups on the SMSI and catalytic performance for formic acid dehydrogenation. In this study, we tried to maximize the content of amino-propyl groups on the surface of mesoporous silica supports (KIE-6) via hydroxylation of KIE-6 surface before amine functionalization and investigated the effect of the content of amine functional groups on the catalytic activity and stability for formic acid dehydrogenation. As a result, Pd/NH2-hydroxylated KIE-6 (Pd/NH2-OH-KIE-6) catalysts with more amine functional groups provided higher initial catalytic activity (595 mol H2 mol catalyst−1h−1) than Pd/NH2-KIE-6 catalysts. However, Pd/NH2-KIE-6 catalysts showed higher catalytic stability in comparison with Pd/NH2-OH-KIE-6 catalysts. After various characterizations of catalysts, it was demonstrated that the enhanced initial catalytic activity of Pd/NH2-OH-KIE-6 catalysts is attributed to the higher ratio of Pd/PdO derived from the increased content of amine groups of NH2-OH-KIE-6 supports. In contrast, the low surface area of NH2-OH-KIE-6 promoted the aggregation of Pd nanoparticles on Pd/NH2-OH-KIE-6 catalysts, which resulted in the lower catalytic stability of Pd/NH2-OH-KIE-6 catalysts than Pd/NH2-KIE-6 catalysts. Thus it was concluded that confinement of Pd nanoparticles to the pores of supports is a more dominant factor to achieve higher catalytic stability, while the initial catalytic activity is affected by the electronic state of Pd nanoparticle determined by the content of amine functional groups on the surface of supports.

Single-Pot Reductive Rearrangement of Furfural to Cyclopentanone over Silica-Supported Pd Catalysts.

Direct one-pot hydrogenation of furfural (FFR) to cyclopentanone (CPO) was investigated over different silica-supported Pd catalysts. Among these, 4% Pd on fumed silica (4%Pd/f-SiO2) showed remarkable results, achieving almost 98% furfural (FFR) conversion with ∼89% selectivity and 87% yield to cyclopentanone at 165 °C and 500 psig H2 pressure. More interestingly, the fumed-silica-supported catalyst tuned the selectivity toward the rearrangement product, i.e., cyclopentanone, whereas all of the other supports were found to give ring hydrogenation as well as side chain hydrogenation products due to their parent Brönsted acidity and specific support properties. X-ray diffraction data revealed the presence of different phases of the face-centered cubic lattice of metallic Pd along with lowest crystallite size of 15.6 nm in the case of the silica-supported Pd catalyst. However, Pd particle size was found to be in the range of 5–13 nm with even dispersion over the silica support, confirmed by high-resolution transmission electron microscopy analysis. While studying the effect of reaction parameters, it was observed that lower temperature gave low furfural conversion of 58% with only 51% CPO selectivity. Similarly, higher H2 pressure lowered CPO selectivity with subsequent increase in 2-methyl furan and ring hydrogenation product 2-methyl furan and 2-methyl tetrahydrofuran. Thus, as per the requirement, the product selectivity can be tuned by varying the type of support and/or the reaction parameters suitably. With the help of several control experiments and the characterization data, a plausible reaction pathway was proposed for the selective formation of cyclopentanone.

Profiling and catalytic upgrading of commercial palm oil-derived biodiesel fuels for high-blend fuels

Commercial palm oil-derived biodiesel fuels (palm BDFs) were thoroughly profiled based on the specifications of international fuel standards. Their main components were found to be fatty acid methyl esters (FAME) with different numbers of double bonds in the fatty acid tails in addition to small amounts of unreactive glycerides and impurities, the concentrations of which varied slightly among the regional producers in Thailand. The fuel properties of the as-received commercial palm BDFs met international fuel standards; unfortunately, the fuel degraded significantly over time, presumably due to the presence of polyunsaturated fatty acid methyl esters (poly-FAME) and impurities. To prevent this degradation, the commercial palm BDFs were upgraded into partially hydrogenated fatty acid methyl esters with outstanding oxidation stability (H-FAME, a new type of biodiesel fuel enriched in monounsaturated fatty acid methyl esters (mono-FAME)) over supported Pd catalysts with metallic Pd nanoparticles as the catalytically active sites in a batch-type glass reactor under mild conditions (80 °C and 0.5 MPa H2). In the upgrading process, the unwanted component poly-FAME, which had low oxidation stability, was selectively converted into the target component, mono-FAME with high oxidation stability. Although the impurities in the commercial palm BDFs poisoned the supported Pd catalysts, particularly the sulfur species, the homemade mesoporous silica-supported Pd catalyst with a high Pd dispersion of 47% gave higher activity and tolerance to the impurities in the synthesis of palm H-FAMEs than the commercial alumina-supported Pd catalyst, which had a low Pd dispersion of 16%. In the accelerated oxidation stability test, the B20 fuels formulated by blending petro-diesel with the palm H-FAMEs with enhanced oxidation stability produced almost no deposits or sludges, whereas the fuels formulated by blending petro-diesel with commercial palm BDFs were seriously degraded and acidified, and formed deposits and sludges. Moreover, the palm H-FAMEs could be further purified by selective removal of the monoglycerides (MG) and steryl glucosides (SG) through wintering and adsorption posttreatments, and were determined to be a reliable BDF source with high safety and security for use in high blend fuels.

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.

Complete catalytic debromination of hexabromocyclododecane using a silica-supported palladium catalyst in alkaline 2-propanol

Although the brominated flame retardant 1,2,5,6,9,10-hexabromocyclododecane (HBCD) has been widely used to reduce the flammability of polymeric materials, it is a toxic and persistent organic compound. In this paper, we report an efficient method for the debromination of HBCD by using a Pd-catalyzed system. HBCD was completely debrominated to the C12 cyclic compounds such as cyclododecatriene, cyclododecadiene, and cyclododecene in a solution of 2-propanol/methanol (99:1, v/v) containing dissolved NaOH in the presence of a silica-supported Pd catalyst (Pd/SiO2) at 35 °C. The reaction achieved product yields of 92% for the bromine-free products and 94% for the released Br ions. In the absence of Pd/SiO2, HBCD was partially debrominated to yield penta-, tetra-, and tribrominated C12 cyclic compounds. The HBCD debromination pathway seems to involve both HBr elimination by reaction with NaOH and Pd-catalyzed hydrodebromination by hydrogen transfer from 2-propanol.

Optimized synthesis of π-extended squaraine dyes relevant to organic electronics by direct (hetero)arylation and Sonogashira coupling reactions.

This study reports on the synthesis and characterization of four molecular π-extended squaraine compounds relevant to the field of organic electronics. The compounds each consist of a bis-indole squaraine core end-capped with indoloquinoxaline units employing three different bridging units, namely thiophene, thiazole, and acetylene. Compound 10 bears a thiophene bridge, 11 consists of a thiophene bridge and fluorinated indoloquinoxaline terminal units, and compounds 12 and 13 are bridged by thiazole and acetylene, respectively. The final compounds are constructed using the atom economical direct (hetero)arylation or the classic Sonogashira carbon-carbon bond formation protocols. Each carbon-carbon bond forming reaction employing thiophene bridges (i.e. synthesis of compounds 10 and 11) has been optimized using the stable and reusable silica supported Pd catalyst, SiliaCat® DPP-Pd, streamlining the synthetic procedure. While compounds 12 and 13 were also accessible using the SiliaCat® DPP-Pd catalyst, the use of Herrmann-Beller and Pd(PPh3)4 catalysts, respectively, lead to improved isolated yields of the final materials. Compounds 10-13 were characterized by thermal gravimetric analysis, cyclic voltammetry, optical absorption spectroscopy, photoluminescence spectroscopy, and each structure was analysed using density functional theory. All compounds exhibit high thermal stability and good solubility in common organic solvents, including in the greener alternative 2-methyl tetrahydrofuran. The reported compounds display stable ambipolar redox behaviour, furthermore, we have demonstrated that the frontier molecular energy levels can be effectively tuned by changing the bridging unit as predicted by density functional theory. Most striking is the drastic optical absorption profile changes observed from this class of materials upon post-deposition film annealing, suggesting molecular rearrangement in the solid-state. The induced changes and fine structure observed upon post-deposition annealing is unique to these π-extended squaraines with nothing like it reported in the literature for related squaraine based materials.

Heck coupling reactions catalysed by Pd particles generated in silica in the presence of an ionic liquid

Silica-supported Pd catalysts were synthesized in the presence of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate. Two samples with extremely low Pd loadings, 0.35Pd and 0.08Pd, with Pd contents 0.35 and 0.08%, respectively, were subjected to further investigations. Structural characterization was performed by ICP-AES and Raman measurements. Raman spectra indicated the presence of the ionic liquid in the Pd-silica samples. The samples were tested as catalysts in the Heck coupling reactions of methyl acrylate and styrene, with substituted bromoarenes and chloroarenes. Both samples proved to be highly efficient catalysts and displayed excellent activities and selectivities for the reactions of activated haloarenes including chloroarenes, which could be efficiently transformed without applying harsh reaction conditions. As expected, the presence of an electron withdrawing group (EWG) on the aromatic ring of the haloarene was found to increase both the conversion and the selectivity to an appreciable extent. For the transformations of bromoarenes, the sample with the lowest Pd loading proved to be a more efficient catalyst. Upon recycling of the catalysts, a considerable activity loss was detected, which was attributed to an extensive leaching of Pd into the solution, as confirmed by hot filtration measurements.

Influences of the Support Property and Pd Loading on Activity of Mesoporous Silica-Supported Pd Catalysts in Partial Hydrogenation of Palm Biodiesel Fuel

Influences of the Support Property and Pd Loading on Activity of Mesoporous Silica-Supported Pd Catalysts in Partial Hydrogenation of Palm Biodiesel Fuel

Vapor phase deoxygenation of heptanoic acid over silica-supported palladium and palladium-tin catalysts

Silica-supported Pd and PdSn catalysts were prepared by ion exchange or incipient wetness impregnation and characterized with H2 chemisorption, X-ray diffraction, in situ Sn K-edge X-ray absorption near edge structure (XANES), and scanning transmission electron microscopy. The activity of the catalysts was evaluated in the deoxygenation of vapor-phase heptanoic acid at 0.1MPa and 573K. A Pd catalyst synthesized via ion exchange formed nanoparticles of 1.1±0.4nm and was more stable in heptanoic acid conversion compared to a Pd catalyst synthesized via incipient wetness impregnation having nanoparticles of 2.4±0.5nm. The addition of Sn to a Pd catalyst by either co-impregnation of precursors or physical mixing of supported monometallic catalysts improved the overall catalyst stability. Moreover, Sn addition expanded the reaction network from primarily decarbonylation over Pd to include dehydration and decarboxylative ketonization over PdSn. Electron microscopy confirmed the physical migration of Sn during catalytic reaction. In situ XANES analysis during the deoxygenation of a carboxylic acid suggests that partially reduced SnOx is the active Sn phase associated with Pd nanoparticles under reaction conditions.

Catalytic Deoxygenation of Octanoic Acid over Supported Palladium: Effects of Particle Size and Alloying with Gold

Catalytic deoxygenation of octanoic acid (OA) to n-heptane was investigated over silica-supported Pd and PdAu catalysts at 260 °C and 1 atm in a fixed-bed microreactor. Pd/SiO2 catalysts were prepared by incipient wetness (IW) and ion exchange (IE). Bimetallic catalysts were prepared using an IE procedure that is known to produce supported PdAu nanoparticles. The Pd nanoparticles (7.5 nm average size) in the Pd/SiO2 (IW) catalyst exhibit well-defined (100) and (111) facets, as evidenced by high-resolution electron microscopy (HREM) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of adsorbed CO. As expected, the smaller nanoparticles (1.5 nm average size) in the Pd/SiO2 (IE) catalyst display strong linear and bridging CO DRIFTS bands. The PdAu/SiO2 (1/1 atomic ratio) catalyst contains 5 nm alloy nanoparticles with Pd-rich surfaces, as evidenced by HREM with energy-dispersive X-ray (EDX) analysis and in situ EXAFS spectroscopy. DRIFTS thermal desorption experiments demonstrated that...

Abatement of CH4 emitted by CNG vehicles using Pd-SBA-15 and Pd-KIT-6 catalysts

Compressed Natural Gas (CNG) engines are growing in interest in the car market due to their ability in the limitation of NOx and CO2 emissions. Unburned methane is harder to oxidize than gasoline-derived unconverted HCs and its strong greenhouse effect induces the development of tailored after treatment technologies. In this work, SBA-15 and in particular KIT-6 have been used as supports for Pd catalysts for the abatement of methane emitted by CNG engines. The synthesized materials have been characterized through XRD, N2-adsorption/desorption, EDX, STEM, and TEM analysis techniques. The influence of different pore structure and size of the mesoporous supports as well as of different Pd loading (in the range 0.25–0.7wt%) on the activity has been investigated. All mesoporous silica supported Pd catalysts showed almost complete conversion of methane, although catalysts with the lowest Pd loadings reached 90% of conversion over 650°C, whereas the maximum Pd loadings allowed to decrease the temperature of complete conversion, with T90 at 405°C by employing the KIT-6 mesoporous silica support.

Preparation of silica-supported Pd nanoparticle catalysts by an alcohol reduction method and evaluation of their catalytic properties in the dechlorination of an aromatic chloride

Reduction of a Pd(II) precursor in refluxing 2-propanol, ethanol, or methanol in the presence of dissolved NaOH afforded silica-supported Pd catalysts designated Pd/SiO2(Pr), Pd/SiO2(Et), and Pd/SiO2(Me), respectively. Pd/SiO2(Pr) consisted of metallic Pd particles (average particle size, 5.1 nm) dispersed in the porous structure of SiO2, whereas the Pd particles on Pd/SiO2(Et) and Pd/SiO2(Me) were larger. The catalytic activity of Pd/SiO2(Pr) in the dechlorination of 2,4,6-trichloroanisole in a solution of 2-propanol containing NaOH was greatly enhanced by the addition of methanol; the optimum rate occurred at 1 % v/v methanol. The activity of Pd/SiO2(Et) was also enhanced by methanol but to a lesser extent than that of Pd/SiO2(Pr). In contrast, Pd/SiO2(Me) exhibited no activity even in the presence of methanol.

Modified KIT-6 and SBA-15-spherical supported metal catalysts for N2O decomposition

Nitric acid and adipic acid plants are the main producers of nitrous oxide (N2O), a greenhouse gas that damages the ozone layer and causes environmental issues. In the present work, an attempt has been made to modify KIT-6 and SBA-15-spherical mesoporous silica to enhance the hydrothermal stability and increase the acidic sites on the surfaces through post salt addition and aluminum (Al) incorporation, respectively, in order to effectively utilize them as supports for different metals (Rh, Ru, Pd, Fe) supported catalysts for N2O decomposition. Each metal loadings of 1wt.% was impregnated onto the modified mesoporous silica support materials. The materials were characterized by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), ammonia temperature programmed desorption (NH3-TPD), nitrogen adsorption/desorption, X-ray diffraction (XRD) and transmission electron microscope (TEM) analysis techniques. The potential of these modified mesoporous silica supported Rh, Ru, Pd or Fe (1wt.%) powder catalysts has been examined in a small laboratory scale reactor under specific N2O decomposition conditions. The order of activity of the metals on the modified mesoporous silica supports was: Rh>Ru>Pd>Fe. The modified mesoporous silica supported Rh, Ru and Fe catalysts showed an enhanced activity for N2O decomposition, compared to the non-modified mesoporous silica supported catalysts, due to an increase in the intermediate acidic sites on the supports. However, a different effect was found for the modified mesoporous silica supported Pd catalysts. The hydrothermal stability of the optimized mesoporous silica supported Rh catalysts indicates that these catalysts could be promising candidates for N2O decomposition application.

Hydrogenation of Phenol Using Silica-Supported Pd and PdAu Catalysts in the Presence of H2 and O2

Abstract 2-Cyclohexen-1-one can be synthesized from phenol using silica-supported Pd catalyst by hydrogenation under coexisting hydrogen and oxygen gases. The effects of hydrogen and oxygen ratio, solvent, and alloying Pd with Au were investigated. Similar transformations toward corresponding cyclic enones were observed in other phenolic compounds.