Hydrogenation Of CO Bonds Research Articles

MIL-101(Cr) entrapped polyol-synthesized iron promoted platinum bimetallic nanoparticles system for synergistic selective hydrogenation of cinnamaldehyde

The interfacial characteristics of platinum (Pt) metal catalysts can be systematically regulated by interacting them with electropositive metals, leading to synergistic interactions for extensive catalytic applications. In this study, an evenly dispersed polyol-synthesized iron (Fe)-promoted Pt bimetallic nanoparticle (BNPs) system was embedded in MIL-101(Cr). The PtFe2@MIL-101(Cr) catalyst unveiled remarkable activity (86%) and selectivity (89%) for the superior hydrogenation of the targeted CO bond of cinnamaldehyde (CAL). The exceptional hydrogenation performance can be credited to the interplay of the geometric and electronic properties arising from charge shuttling between Fe and Pt within the homogenously distributed Pt–Fe bimetallic nanoparticle system. The experimental results indicate enhanced valence electrons in the Pt d-band through the mutual synergetic interface between the Pt and Fe BNPs. Consequently, these Fe–Pt sites functioned as interfacial electrophilic and nucleophilic (Lewis acid-base) sites, enhancing H2 activation and facilitating CO bond conversion to yield unsaturated cinnamal alcohols (COL). Additionally, the narrow pores of MIL-101(Cr) encapsulating the Pt–Fe BNPs induced steric hindrance, allowing only CO bond hydrogenation. Furthermore, the PtFe2@MIL-101(Cr) catalyst maintained its optimal hydrogenation performance over five cycles, demonstrating no substantial loss in either CAL conversion or COL yield, thus endorsing the universal practical applicability of the catalyst.

Design of Pt@Sn core–shell nanocatalysts for highly selective hydrogenation of cinnamaldehyde to prepare cinnamyl alcohol

The selective hydrogenation of cinnamaldehyde (CAL) to prepare cinnamyl alcohol (COL) is challenging as the unwanted hydrogenation of CC bond in CAL is thermodynamically more favorable than the hydrogenation of CO bond. We herein designed core–shell structured nanoparticles (NPs) that consisted of Pt cores and Sn shells to catalyze the CAL to COL conversion. By simply changing the amount of Sn precursor, we generated Pt@Sn NPs with different Sn shell thickness and catalytic performance. Among the samples, Pt@Sn/SiO2 with Pt/Sn of 1/1 achieved the highest CAL conversion (87.2 %) as well as the COL selectivity (95.4 %), which were 5-fold and 6-fold, respectively, higher than those of Pt/SiO2. This catalyst was also applicable to the hydrogenation of other α, β-unsaturated aldehyde and unsaturated carbonyl compounds. Both experiments and theoretical calculations indicated that the strong Pt-Sn interaction and the partial coverage of Pt by Sn facilitated their adsorption of CO bonds, thus enhancing the conversion of CAL and the selectivity towards COL.

Selective hydrogenation of crotonaldehyde over Ir/TiO2 catalysts: Unraveling the metal-support interface related reaction mechanism

For the supported catalysts for the selective hydrogenation of α, β - unsaturated aldehyde with H2, tailoring of metal - support interfacial effect to improve reaction performance is a significant but challenging subject. In this work, we regulated both the size regimes of the Ir deposits (single atom, nanocluster and nanoparticle) and the crystal plane of anatase TiO2 (TiO2(101), TiO2(100) and TiO2(001)) so as to alter the Ir-TiOx interfacial properties, in order to unravel reaction mechanism of selective hydrogenation of crotonaldehyde over the Ir/TiO2 catalysts. Both the activity and selectivity to crotyl alcohol increased as the Ir size grew from single atom to nanoparticle, ascribed to high Ir0 content, high concentration of surface defects and prominent H-spillover effect on the Ir nanoparticles. Moreover, the in situ Fourier transform infrared spectroscopy (FTIR) and density functional theory (DFT) calculations demonstrated that an end-on CO adsorption mode for crotonaldehyde molecule was favored at the Ir-TiOx interface particularly at high H coverage, which thus facilitated the hydrogenation of CO bond to form crotyl alcohol. Moreover, the highest reactivity of the Ir nanoparticles was evidenced by the lowest reaction barrier. These results explicitly demonstrate that larger metal nanoparticles and adsorption geometry of the reactant at the metal - support interface are vital for improved catalytic performance, which would shed light on the ingenious catalyst design.

Synergistic contribution of metal–acid sites in selective hydrodeoxygenation of biomass derivatives over Cu/CoOx catalysts

The efficient hydrodeoxygenation (HDO) of biomass derivatives to yield specific products is a significant yet challenging task. In the present study, a Cu/CoOx catalyst was synthesized using a facile co-precipitation method, and subsequently used for the HDO of biomass derivatives. Under optimal reaction conditions, the conversion of 5-hydroxymethylfurfural reached 100% with a selectivity of ∼99% to 2,5-diformylfuran. In combination with the experimental results, systematic characterizations revealed that CoOx, as the acid site, tended to adsorb CO bonds, and the metal sites of Cu+ were inclined to adsorb CO bonds and enhance CO bond hydrogenation. Meanwhile, Cu0 was the main active site for 2-propanol dehydrogenation. The excellent catalytic performance could be attributed to the synergistic effects of Cu and CoOx. Further, by optimizing the ratio of Cu to CoOx, the Cu/CoOx catalysts exhibited notable performance in HDO of acetophenone, levulinic acid, and furfural, which verified the universality of the catalysts in the HDO of biomass derivatives.

Metal-metal oxide synergistic catalysis: Pt nanoparticles anchored on mono-layer dispersed ZrO2 in SBA-15 for high efficiency selective hydrogenation

It is generally believed that noble metal catalysts exhibited higher activity for selective hydrogenation, while metal oxides were almost inactive. Here, we report metal-metal oxide synergistic catalysis for high efficiency selective hydrogenation by a hybrid nano-structure Pt/@-ZrO2/SBA-15 catalyst, which was fabricated by anchored Pt nanoparticles on the mono-layer dispersed ZrO2 film layer coated in SBA-15 support via a photochemical route. This Pt/@-ZrO2/SBA-15 catalyst exhibited remarkable catalytic activity in the selective hydrogenation of CO bond, NO2, and CC bond. For the selective hydrogenation of benzaldehyde, conversion >99.9% was achieved with >99% selectivity, and the turnover frequency (TOF) can be achieved up to 4822 h−1, which was much higher than that of the atomically dispersed Pd1/TiO2-EG catalyst (1002 h−1) reported in the literature, no decay in the activity was observed by several cycles. Combined the experimental and characterization results, proved that the ZrO2 was dispersed in a mono-layer in the channel of SBA-15, and the results showed that an appropriate loading of ZrO2 in this catalyst could maximize the advantage of this hybrid nano-structure to achieve the best catalytic activity. The superior activity of Pt/@-ZrO2/SBA-15 was attributed to the synergistic catalysis, strong interface electronic effect, and the unique properties of the special hybrid nano-structure. This work demonstrated synergistic catalysis of metal Pt nanoparticles and monolayer dispersion ZrO2 for high efficiency selective hydrogenation.

Identifying the activity origin of silver catalysts induced by interfacial electron localization for regioselective C[sbnd]O bond hydrogenation

Deciphering intrinsic reactive sites of metal–oxide catalysts, where the outer surface and/or interfaces coupled with oxygen species in the vicinity of nanoparticles concurrently work, remains a challenge. Given the extreme complexity of heterogeneous catalysis (e.g., metal catalysts for preliminary hydrogenation process), catalytically active sites, the activity origin, and reaction mechanism generally present a so-called 'black box'. Herein, Ag/ZrO2−x achieves a higher intrinsic hydrogenation rate for selective scission of CO bond per mass Ag than the reference Ag/SiO2 catalyst, as illustrated by the preliminary hydrogenation of dimethyl oxalate to methyl glycolate. The in-depth characterization revealed that the Agδ+–Ov–Zr3+ (Agδ+–O–Zr4+, Ov refers to as oxygen vacancy) structure could be engineered owing to the higher affinity of Ag for the partially reduced ZrO2 surface and heteroatom junctions (in preference to the inert support, such as SiO2 and Al2O3). Furthermore, the local environment of different crystallite phases (tetragonal or monoclinic ZrO2) induced tunable (electronic) metal–support interactions (EMSIs), resulting in enhanced catalytic activity and ultra-stability for CO bond hydrogenation. XPS, methyl acetate-TPD, and in situ DRIFTS results unveiled the activity origin of silver–oxide systems, where the location of active metal sites for distinct functionalities over superficial and interfacial phases was validated. The mediated Ov was verified to stabilize the thermodynamically unstable metallic (Ag0) and charged silver species (Ag+ or Agnδ+). More importantly, time-resolved DRIFTS confirmed the crucial interfacial sites of Ag–ZrO2−x for regioselective CO bond adsorption and activation. Further, the distinct active sites over Ag–ZrO2−x may release the altered reaction mechanisms, i.e., conventional Langmuir–Hinshelwood (LH) on Ag/SiO2 versus quasi Mars–Van Krevelen process (Ag–ZrO2−x), which presents the new pathway for regioselective CO bond hydrogenation. The coordinated EMSIs were proposed as the origin of the catalytic activity caused by the synergistic catalysis of the interfacial/superficial sites. These findings rationalize the underlying understanding of the EMSI and highlight the instructive role for perceiving the structure-performance relationships and the activity origin in heterogeneous catalysts, thus moving away from the 'black-box' cognition.

Enhanced selective hydrogenation of glycolaldehyde to ethylene glycol over Cu0-Cu+ sites

Selective hydrogenation of hydroxyaldehydes to polyalcohols is challenging due to the competitive hydrogenation of CO and CO. This study develops heterogeneous Cu catalysts for the selective synthesis of ethylene glycol via batch liquid-phase hydrogenation of glycolaldehyde. SiO2 supported Cu, fabricated by ammonia evaporation, enables to catalyze the CO bond hydrogenation with retaining the CO bond intact, yielding higher selective hydrogenation activity with ethylene glycol selectivity up to 99.8 % relative to MgO, Al2O3, CeO2, and TiO2 supports and Cu/SiO2 synthesized by deposition–precipitation and impregnation. Characterizations confirm that highly efficient 20Cu/SiO2-AE-623 K catalyst fabricated by ammonia evaporation is featured with larger Cu0 and Cu+ surface areas, of which the Cu+ species created from reducing copper phyllosilicate exhibit higher reactivity. A synergistic effect between Cu+ and Cu0 facilitates the selective adsorption/activation of glycolaldehyde on Cu+ sites and the dissociation of H2 on Cu0 sites, bringing a remarkable improvement in the selective hydrogenation performance.

Effects of fertilization on the triafamone photodegradation in aqueous solution: Kinetic, identification of photoproducts and degradation pathway.

Triafamone is a highly effective, low toxicity sulfonamide herbicide widely used for weeding paddy fields. The triafamone photodegradation in water environment must be explored for its ecological risk assessment. In this work, the effects of chemical fertilizer (urea, diammonium phosphate, potassium chloride, and potassium sulfate), urea metabolites (CO32- and HCO3-), and organic fertilizers (unfermented organic fertilizer [UOF] and fermented organic fertilizer [FOF]) on the triafamone photodegradation in aqueous solution under simulated sunlight were evaluated. Results showed that the triafamone photodegradation rate was unaffected by urea. The half-life of triafamone decreased from 106.8h to 68.4h with increasing diammonium phosphate concentration. Potassium chloride, potassium sulfate, CO32-, and HCO3- could accelerate the triafamone photodegradation at all concentrations, whereas the degradation rate of triafamone decreased when the concentration of potassium sulfate or CO32- was 2000mg/L. Triafamone photodegradation was promoted by 20-200mg/L UOF and FOF but decreased to 236.6 and 142.3h when the concentration reached 2000mg/L. Twenty-three transformation products were isolated and identified from triafamone by using ultra-performance liquid chromatography with quadrupole time-of-flight mass spectrometry under simulated sunlight irradiation, and the kinetic evolution of these products was explored. Five possible degradation pathways were inferred, including the cleavage of C-N, C-C, and C-O bonds; CO bond hydrogenation; the cleavage of triazine ring; the cleavage of the sulfonamide bridge; hydroxylation; hydroxyl substitution; methylation; demethylation; amination; and rearrangement. In summary, these results are important for elucidating the environmental fate of triafamone in aquatic systems and further assessing environmental risks.

Promoted chemoselective crotonaldehyde hydrogenation on zirconia-doped SiO2 supported Ag catalysts: Interfacial catalysis over ternary Ag–ZrO2–SiO2 interfaces

In gas-phase chemoselective hydrogenation of crotonaldehyde on Ag-based catalysts, zirconia doping on silica supports was found to improve catalytic performance in terms of unsaturated alcohol selectivity, hydrogenation activity, and stability. The surface modification of silica by zirconia doping favors the fine dispersion of Ag species due to the enhanced quantity and strength of surface acid sites, which enable construction of abundant catalytic sites effective for CO bond hydrogenation. High crotyl alcohol selectivity, exceeding 80%, and significant inhibition of monohydrogenation on the CC bond were observed on the optimal Ag/Zr–SiO2 catalyst. Dynamic O2 chemisorption measurement revealed that the pure Ag powders did not chemisorb O2 irreversibly under 323 K, but SiO2 or Zr–SiO2 supported Ag catalysts did. The amounts of Ag active for O2 chemisorption, which are at least one order of magnitude lower than that of surface Ag derived from TEM and XRD characterizations, match well with the perimeter interface Ag of hemispherical particles. A strong correlation between hydrogenation activity and O2 uptake on those Ag/SiO2 and Ag/Zr–SiO2 catalysts with different Ag dispersions and deactivation degrees was observed, implying that the effective catalytic sites for crotonaldehyde chemoselective hydrogenation may originate from accessible interface sites with unique redox properties. Catalyst induction and deactivation were observed on both Ag/SiO2 and Ag/Zr–SiO2 catalysts in real catalytic operation. Changes in metal stable interface structure, rather than metal aggregation and coagulation, are assumed to be the main cause of irreversible catalyst deactivation, because the apparent Ag particle sizes changed slightly, but the oxygen chemisorption ability deteriorated considerably. Electropositive Ag sites interacting with neighboring oxygen from oxide supports at the ternary Ag–ZrO2–SiO2 interface are proposed to account for highly selective CO bond hydrogenation to produce the desired unsaturated alcohol.

Pd/MgAl-LDH nanocatalyst with vacancy-rich sandwich structure: Insight into interfacial effect for selective hydrogenation

In this work, a Pd/MgAl-LDH catalyst was synthesized by the ion-exchange and liquid-reduction process (IE), with impregnation method (IM) as contrast, to study the difference in the interfacial structure induced by the preparation methods and the catalytic behavior for selective hydrogenation of 2-ethylanthraquinone. STEM-EDS measurement reveals that the IE-Pd/MgAl-LDH catalyst possesses an obvious sandwich structure of which Pd nanoparticles uniformly located in the LDH interlayer space, and therefore exhibits more Pd-LDH interface sites due to the high intimacy. More importantly, it was confirmed that the Pd-LDH interface structure was characterized by rich oxygen vacancies (Vo) due to the loss of surface hydroxyl groups on the LDH layer during the ion-exchange process. As expected, the IE-Pd/MgAl-LDH catalyst exhibited a 127% higher H2O2 yield than that of IM-Pd/MgAl-LDH catalyst. High activity was attributed to the facilitated hydrogen activation resulting from significantly enhanced hydrogen spillover over the Pd-LDH interface structure. Preferred selectivity was owing to the special adsorption mode of CO bond interacted with the Pd-Vo interfacial sites, which leads to the selective activation of CO bond. This work develops a feasible approach to fabricate the metal-hydroxide interface structure and provides a fundamental understanding on interfacial effect toward selective hydrogenation of CO bonds.

Kinetics of cinnamaldehyde hydrogenation in four phase system

The kinetics of cinnamaldehyde hydrogenation in four phase system viz. gas (hydrogen)-liquid (cinnamaldehyde + toluene)-liquid (aqueous KOH)-solid (catalyst, 5% Pt/C), [GLLS] system has been studied in this work. As reported, addition of aqueous alkali in hydrogenation of unsaturated aldehydes like cinnamaldehyde shifts selectivity towards unsaturated alcohol, cinnamyl alcohol. The promotion action by alkali metals for improving selectivity towards cinnamyl alcohol involves changes in the adsorption mechanism of the cinnamaldehyde in a way that CO bond get preferentially hydrogenated. In cinnamaldehyde hydrogenation in presence of promoters two different catalytic sites can be considered, each for CO and CC bond hydrogenation. In accordance with this consideration and as demonstrated in various studies on hydrogenation of unsaturated aldehydes, further hydrogenation of intermediate-cinnamyl alcohol (CC bond hydrogenation) occurs on Pt only sites while cinnamaldehyde and intermediate hydrocinnamaldehyde (both involving CO bond hydrogenation) are hydrogenated on catalytic sites affected by promoters. This preferential adsorption and hydrogenation through CO bond leads to the increased selectivity of cinnamyl alcohol. Although, many authors have studied cinnamaldehyde hydrogenation using various promoters, there are very few reports on kinetics in which this two site approach behind promotion action has been considered. The effect of various operating parameters on the rates of hydrogenation was studied and the two site Langmuir-Hinshelwood type of kinetic model was used for evaluating the kinetic parameters by fitting experimental data. The thermodynamic model for estimating the solubility of hydrogen in the reaction mixture was incorporated with this kinetic model.

Tuning nano-nickel selectivity with tin in flow hydrogenation of 6-methyl-5-hepten-2-one by surface organometallic chemistry modification

Chemoselective flow hydrogenation of 6-methyl-5-hepten-2-one was performed over nano-nickel catalysts. The parent catalyst composed solely of nickel nanoparticles grafted on the polymeric resin exhibited high activity and selectivity towards CC bond saturation but its modification with small quantities of tin significantly increased its ability to perform CO bond hydrogenation. The post-synthetic modification of the parent catalyst was achieved by surface organometallic chemistry approach and performed in the same flow micro-reactor, which was used for the catalytic studies, providing a methodology for online modification of parent catalysts.

The composition of Ni-Mo phases obtained by NiMoOx-SiO2 reduction and their catalytic properties in anisole hydrogenation

The specific features of the formation of nickel- and molybdenum-containing phases during the reduction of the oxide precursor of the NiMoOx-SiO2 catalyst with hydrogen at three different temperatures (470, 570, and 750°C) were studied. The reduction behavior was investigated and the reduction temperature of oxide forms was determined with the use of the methods of temperature-programmed reduction, X-ray diffraction analysis, and X-ray photoelectron spectroscopy. It was shown that, at a reduction temperature from 470 to 570°C, one can observe the formation of NiMoOx particles with the NiO-type structure, Ni-Mo alloys of different composition, and MoO2, which pass into the metallic phases Mo, Ni3Mo, and NixMo1-x at 750°C. Nickel located at the surface is completely reduced to the metallic state in the temperature range of 300–750°C, the Mo° content increases with the growing of treatment temperature and reaches 100% at 750°C. Based on the data obtained, a reduction scheme for the catalytic system is proposed. The catalytic properties of the systems obtained are studied in the anisole hydrogenation reaction at a temperature of 300°C and a hydrogen pressure of 6MPa. The results of catalytic experiments showed that the 750-NiMo-SiO2 catalyst possesses the highest specific activity in the anisole hydrogenation, which is probably due to the complete reduction of nickel oxide forms and molybdenum to metallic forms, which are highly active in the hydrogenation of CO bonds and aromatic rings. The highest selectivity in the formation of oxygen-free products can be attributed to the catalysts reduced at 470–570°C and whose active component contains coordinatively unsaturated molybdenum atoms. The most stable during the thermal treatment in acetic acid is the 750-NiMo-SiO2 catalyst, which can be explained by the fact that it contains Ni-Mo alloys highly stable in the acid medium.

Elucidation of the active phase in PtSn/SAPO-11 for hydrodeoxygenation of methyl palmitate

SAPO-11 zeolite-supported PtSn bimetallic catalysts (PtSn/SAPO-11) were prepared using a co-impregnation method for simultaneous selective hydrodeoxygenation of methyl palmitate and isomerization of deoxygenated hydrocarbons. The PtSn catalyst exhibited high isomerization activity and hydrodeoxygenation selectivity, and was superior to the monometallic Pt/SAPO-11 catalyst. The Pt/SAPO-11 catalyst was more active for CC bond cleavage, resulting in a considerable formation of C15 hydrocarbons. The PtSn/SAPO-11 catalyst was more efficient for CO bond hydrogenation, affording higher selectivity to C16 hydrocarbons. In the studied PtSn catalyst, the platinum content was constant at 0.3wt% and the atomic ratio of Sn/Pt was varied from 1 to 3. The result of the catalytic test suggests that it is necessary to control tin surface density in order to obtain a well-balanced Pt–SnO2−x function and a Pt–Sn alloy as well. The highest performance in the tandem hydrodeoxygenation–isomerization of methyl palmitate was observed at the Sn/Pt ratio of 2; for this catalyst, the isomerization yield obtained at 375°C was 4 times higher than the monometallic Pt catalyst. After tin addition, Pt nanoparticles were highly dispersed on the support with an average size of ∼4nm. HRTEM observations and FT-IR studies of CO adsorption indicate that a portion of Sn interacted with Pt, forming Pt–Sn alloys; other Sn species were formed in the form of tin oxides, likely SnO2−x (0<x<2), and were mainly present on the periphery of Pt nanoparticles. The occurrence of SnO2−x species is crucial for the hydrodeoxygenation pathway; however, excessive addition of tin would block the Pt and PtSn active sites, resulting in a decrease in the catalytic activity. The presence of Pt–Sn alloys is the most remarkable reason for its high isomerization activity.

Construction of Cu/ZrO2/Al2O3 composites for ethanol synthesis: Synergies of ternary sites for cascade reaction

The hydrogenation of dimethyl oxalate (DMO) to ethanol involves the stepwise hydrogenation of CO bonds and hydrogenolysis of CO bonds. In the present work, the assembly of ternary active sites (Cu, ZrO2, Al2O3 sites) for this reaction was investigated. The calcination temperature was demonstrated to have profound influences on the catalytic performance, evolutions of texture and structure properties and functionality of active phases of the ternary catalysts with similar compositions. The Cu/ZrO2/Al2O3 catalyst calcined at a high temperature of 750°C exhibited an ethanol yield up to 97.4% and stable performance (>200h). Key to success is the concurrence of the stable metallic Cu sites with more proportions of Cu+ sites, active crystalline ZrO2 phases and sufficient acid sites which were generated upon high temperature calcination. The high-temperature calcination annealed Cu particles into large ones, facilitating the high stability. Another factor for the good stability is the formation of CuAl2O4 spinel and the resulted strong interactions between Cu and Al2O3 after reduction. Overall, the design of efficient multifunctional catalysts for hydrogenation/hydrogenolysis of CO/CO bonds lies in the adequate assembly and modulation of textural, structural and surface properties of catalysts. The structure-performance relationships were well elucidated by the analysis of structural and surface properties of active phases and catalytic performance, which provide more rational choices for making high-performance catalysts for CO hydrogenation and CO hydrogenolysis reactions.

Observing the in situ chiral modification of Ni nanoparticles using scanning transmission X-ray microspectroscopy

Enantioselective heterogeneous hydrogenation of CO bonds is of great potential importance in the synthesis of chirally pure products for the pharmaceutical and fine chemical industries. One of the most widely studied examples of such a reaction is the hydrogenation of β-ketoesters and β-diketoesters over Ni-based catalysts in the presence of a chiral modifier. Here we use scanning transmission X-ray microscopy combined with near-edge X-ray absorption fine structure spectroscopy (STXM/NEXAFS) to investigate the adsorption of the chiral modifier, namely (R,R)-tartaric acid, onto individual nickel nanoparticles. The C K-edge spectra strongly suggest that tartaric acid deposited onto the nanoparticle surfaces from aqueous solutions undergoes a keto-enol tautomerisation. Furthermore, we are able to interrogate the Ni L2,3-edge resonances of individual metal nanoparticles which, combined with X-ray diffraction (XRD) patterns showed them to consist of a pure nickel phase rather than the more thermodynamically stable bulk nickel oxide. Importantly, there appears to be no “particle size effect” on the adsorption mode of the tartaric acid in the particle size range ~90–~300nm.

Selective hydrogenation of cinnamaldehyde over Pt nanoparticles deposited on reduced graphene oxide

The selective hydrogenation of cinnamaldehyde was investigated with Pt nanoparticles deposited on reduced graphene oxide (Pt/RGO). Compared with carbon nanotubes (CNTs) or activated carbon (AC) as support, Pt/RGO showed the best activity and selectivity for the hydrogenation of CO bond.

ChemInform Abstract: Model Studies of Heterogeneous Catalytic Hydrogenation Reactions with Gold

AbstractReview: 55 refs.

Deoxygenation of propionic acid on heteropoly acid and bifunctional metal-loaded heteropoly acid catalysts: Reaction pathways and turnover rates

Reaction pathways of the gas-phase deoxygenation of propionic acid in the presence of heteropoly acid and bifunctional metal-loaded heteropoly acid catalysts were investigated in a fixed-bed reactor at 250–400°C in flowing H2 or N2. Silica-supported H3PW12O40 (HPW) and bulk acidic salt Cs2.5H0.5PW12O40 (CsPW), both in H2 and in N2, exhibited ketonisation activity between 250 and 300°C to yield 3-pentanone, CsPW being more selective than HPW. At 400°C, HPW and CsPW were active for decarbonylation and decarboxylation of propionic acid to yield ethene and ethane, respectively. Loading Pd or Pt onto CsPW greatly enhanced decarbonylation in flowing H2 but had little effect in N2. Similar performance exhibited Pd/SiO2 and Pt/SiO2, giving almost 100% selectivity to ethene in H2. These results are consistent with hydrodeoxygenation of propionic acid on Pd and Pt, suggesting that hydrogenolysis of CC bond plays essential role. In contrast to the Pd and Pt catalysts, Cu catalysts, Cu/CsPW and Cu/SiO2, were both active in hydrogenation of CO bond to yield propanal and 1-propanol. Turnover rates of propionic acid conversion on metal catalysts followed the order Pd>Pt>Cu for both CsPW-supported and silica-supported metal catalysts.

Controlling hydrogenation of C[dbnd]O and C[dbnd]C bonds in cinnamaldehyde using silica supported Co-Pt and Cu-Pt bimetallic catalysts

Liquid phase hydrogenation of cinnamaldehyde was evaluated over SiO2 supported Co-Pt and Cu-Pt bimetallic and Co, Cu, Pt monometallic catalysts in a batch reactor. H2-temperature-programmed reduction (H2-TPR) was utilized to characterize the reduction behavior and pulse CO chemisorption measurement was performed to characterize the number of active sites of the catalysts. Transmission electron microscopy (TEM) analysis was used to characterize metallic particle size distribution and extended X-ray absorption structure (EXAFS) measurements were performed to verify the bimetallic bond formation. The reactor evaluation results show that Co-Pt and Cu-Pt bimetallic catalysts exhibit much higher hydrogenation activity than the corresponding monometallic catalysts, and Co-Pt shows much higher selectivity toward CO bond hydrogenation than Cu-Pt. The trend of hydrogenation activity and selectivity is consistent with previous studies of the hydrogenation of unsaturated aldehydes on model bimetallic surfaces.