Pt nanoparticles entrapped in ordered mesoporous carbons:An efficient catalyst for the liquid-phase hydrogenation of nitrobenzene and its derivatives

Pt nanoparticles entrapped in ordered mesoporous CMK-3 carbons with p6mm symmetry were prepared using a facile impregnation method, and the resulting materials were characterized using X-ray diffraction spectroscopy, N2 adsorption-desorption, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The Pt nanoparticles were highly dispersed in the CMK-3 with 43.7% dispersion. The Pt/CMK-3 catalyst was an effective catalyst for the liquid-phase hydrogenation of nitrobenzene and its derivatives under the experimental conditions studied here. The Pt/CMK-3 catalyst was more active than commercial Pt/C catalyst in most cases. A highest turnover frequency of 43.8 s-1 was measured when the Pt/CMK-3 catalyst was applied for the hydrogenation of 2-methyl-nitrobenzene in ethanol under optimal conditions. It is worthy of note that the Pt/CMK-3 catalyst could be recycled easily, and could be reused at least fourteen times without any loss in activity or selectivity for the hydrogenation of nitrobenzene in ethanol.

Kinetics of Liquid-Phase Hydrogenation of Toluene Catalyzed by Hydrogen Storage Alloy MlNi_5

The kinetics of liquid-phase hydrogenation of toluene catalyzed by MlNi_5 was studied by investigating the influences of the reaction temperature and pressure on the mass transfer-reaction processes inside the slurry. The results show that the reaction rate accelerates when the reaction temperature increases, and reaches its maximum at about 490 K, but if temperature is higher than 510 K, the reaction rate decreases rapidly. The whole reaction process is controlled by the reaction at the surface of the catalyst particles. The mass transfer resistance at gas-liquid interface and that from the bulk liquid phase to the surface of the catalyst particle can be neglected. The apparent reaction rate is zero order for toluene concentration and first order for hydrogen concentration in the liquid phase. The kinetic model is obtained. The kinetic model fits the experimental data very well. The apparent activation energy of the hydrogen absorption reaction of MlNi_5-toluene slurry system is 41.01 kJ·mol^(-1).

Kinetics of Liquid-Phase Hydrogenation of Benzene in a Metai Hydride Slurry System Formed by MlNi_5 and Benzene

The kinetics of liquid-phase hydrogenation of benzene in misch metai nickel-five (MINi5) and benzene slurry system was studied by investigating the influences of the reaction temperature, pressure, alloy concentration and stirring speed on the mass transfer-reaction processes inside the slurry. The results show that the whole process is controlled by the reaction at the surface of the catalyst. The mass transfer resistance at gas-liquid interface and that from the bulk liquid phase to the surface of the catalyst particles are negligible. The apparent reaction rate is zero order for benzene concentration and first order for hydrogen concentration in the liquid phase. The kinetic modei obtained fits the experimental data very well. The apparent activation energy of the hydrogen absorption reaction of MINi5-C6H6 slurry system is 42.16kJ·mol-1.

A comparative study of Ni/Al_2O_3–SiC foam catalysts and powder catalysts for the liquid-phase hydrogenation of benzaldehyde

In this study, Al_2O_3-washcoated SiC(Al_2O_3–SiC) foams and Al_2O_3 powder were employed as the supports of a Ni catalyst for the liquid-phase hydrogenation of benzaldehyde. A series of Ni/Al_2O_3–SiC foam catalysts and Ni/Al_2O_3 powder catalysts with a Ni loading from 10 wt% to 37 wt% of the weight of Al_2O_3 were first prepared by a deposition–precipitation(DP) method. The catalytic activity and recyclability of both kinds of catalysts were then compared. Although it had a smaller accessible surface area with the reactant, the foam catalyst with a Ni loading of 16 wt% exhibited a slightly higher conversion of benzaldehyde after 6 h(of 99.3%) in comparison with the Ni/Al_2O_3 catalyst with identical Ni loading(conversion of 97.5%). When the Ni loading increased from 16 wt% to 37 wt%, the reaction rate obtained with the foam catalyst increased significantly from 0.108 to 0.204 mol L^(-1)h^(-1), whereas the reaction rate obtained with the powder catalyst increased from 0.106 to 0.123 mol L^(-1)h^(-1). Furthermore, the specific activity(moles of benzaldehyde consumed by 1 g min^(-1)of Ni) of the foam catalyst with a Ni loading above 30 wt% was superior to that of the powder catalyst because of its smaller Ni-particle size and higher mass-transfer rate. The foam catalyst displayed a high recyclability as a function of run times owing to the strong interaction between the Ni component and the Al_2O_3 coating. The conversion of benzaldehyde over the foam catalyst remained almost unchanged after being used 8 times. In comparison, a drop of 43% in the conversion of benzaldehyde with the powder catalyst was observed after being used 7 times due to the leaching of the Ni component.

Liquid-Phase Catalytic Hydrogenation of Furfural in Variable Solvent Media

Water is the most abundant compound inherently existing in bio-oils. Thus understanding the role of water within bio-oils upgrading process is essential for future engineering scale-up design. In this study, furfural was chosen as bio-oils model compound, and the catalytic hydrogenation of furfural over commercial 5%, Ru/C catalyst was firstly investigated in a series of gradient variable water/ethanol mixture solvents. Water had a significant effect on the distribution of product yields. The dominant reaction pathways varied with the water contents in the water/ethanol mixture solvents. Typically, when ethanol was used as the solvent, the main products were obtained by the hydrogenation of carbonyl group or furan ring. When pure water was used as the solvent, the rearrangement reaction of furfural to cyclopentanone should be selectively promoted theoretically. However, serious polymerization and resinification were observed herein in catalytic hydrogenation system of pure water. The catalyst surface was modified by the water-insoluble polymers, and consequently, a relative low yield of cyclopentanone was obtained. A plausible multiple competitive reaction mechanism between polymerization reaction and the hydrogenation of furfural was suggested in this study. Characterizations(TG,FT-IR,SEM)were employed to analyze and explain our experiments.

Relationship between hydrogenation degree and pyrolysis performance of jet fuel

Understanding the relationship between the chemical composition and pyrolysis performance of endothermic hydrocarbon fuel(EHF) is of great significance for the design and optimization of advanced EHFs. In this work, the effect of deep hydrogenation on the pyrolysis of commercial RP-3 is investigated.Fuels with different hydrogenation degrees were obtained by the partially and completely catalytic hydrogenation and their pyrolysis performances were investigated using an apparatus equipped with an electrically heated tubular reactor. The results show that with the increase of hydrogenation degree, fuel conversion almost remains constant during the pyrolysis process(500-650°C, 4 MPa);however, the heat sink increases slightly, and the anti-coking performance significantly improves, which are highly related to their H/C ratios. Detailed characterisations reveal that the difference of the pyrolysis performance can be ascribed to the content of aromatics and cycloalkanes: the former are prone to initiate secondary reactions to form coking precursors, while the latter could act as the hydrogen donor and release hydrogen, which will terminate the radical propagation reactions and suppress the coke deposition. This work should provide the guidance for upgrading EHFs by modulating the composition of EHFs.

Understanding the dehydrogenation properties of Mg(0001)/MgH_(2)(110)interface from first principles

Magnesium hydride is one of the most promising solid-state hydrogen storage materials for on-board application.Hydrogen desorption from MgH_(2) is accompanied by the formation of the Mg/MgH_(2) interfaces,which may play a key role in the further dehydrogenation process.In this work,first-principles calculations have been used to understand the dehydrogenation properties of the Mg(0001)/MgH_(2)(110) interface.It is found that the Mg(0001)/MgH_(2)(110) interface can weaken the Mg-H bond.The removal energies for hydrogen atoms in the interface zone are significantly lower compared to those of bulk MgH_(2).In terms of H mobility,hydrogen diffusion within the interface as well as into the Mg matrix is considered.The calculated energy barriers reveal that the migration of hydrogen atoms in the interface zone is easier than that in the bulk MgH_(2).Based on the hydrogen removal energies and diffusion barriers,we conclude that the formation of the Mg(0001)/MgH_(2)(110) interface facilitates the dehydrogenation process of magnesium hydride.

Enhanced Ethylene Production from Electrocatalytic Acetylene Semi-hydrogenation Over Porous Carbon-Supported Cu Nanoparticles

Electrocatalytic semi-hydrogenation of acetylene(C_(2)H_(2))over copper nanoparticles(Cu NPs)offers a promising non-petroleum alternative for the green production of ethylene(C2H4).However,server hydrogen evolution reaction(HER)competition in this process prominently decreases C2H4 selectivity,thereby hindering its practical application.Herein,a Cu-based composite catalyst,wherein porous carbon with nanoscale pores was used as a support,is constructed to gather the C_(2)H_(2) feedstocks for suppressing the undesirable HER.As a result,the as-prepared catalyst exhibited C_(2)H_(2) conversion of 27.1%and C_(2)H_(4) selectivity of 88.4%at a C2H4 partial current density of 0.25 A/cm^(2) under optimal−1.0 V versus reversible hydrogen electrode(RHE)under the simulated coal-derived C_(2)H_(2) atmosphere,significantly outperforming the single Cu NPs counterparts.In addition,a series of in situ and ex situ experimental results show that not only the porous nature of the carbon support but also the stabilized Cu^(0)–Cu^(+) dual active sites through the strong metal–support interactions enhance the adsorption capacity of C_(2)H_(2),leading to high C_(2)H_(2) partial pressure,restraining the HER and thus improving the C2H4 selectivity.

Facile molybdenum and aluminum recovery from spent hydrogenation catalyst

Industrial catalyst waste has emerged as a hazardous pollutant that requires safe and proper disposal after the unloading process.Finding a valuable and sustainable strategy for its treatment is a significant challenge compared to traditional methods.In this study,we present a facile method for the recovery of molybdenum and aluminum contents from spent Mo-Ni/Al_(2)O_(3) hydrogenation catalysts through crystallization separation and coprecipitation.Furthermore,the recovered molybdenum and aluminum are utilized as active metals and carriers for the preparation of new catalysts.Their properties were thoroughly analyzed and investigated using various characterization techniques.The hydrogenation activity of these newly prepared catalysts was evaluated on a fixed-bed small-scale device and compared with a reference catalyst synthesized from commercial raw reagents.Finally,the hydrogenation activity of the catalysts was further assessed by using the entire distillate oil of coal liquefaction as the raw oil,specifically focusing on denitrogenation and aromatic saturation.This work not only offers an effective solution for recycling catalysts but also promotes sustainable development.

Microenvironment and electronic state modulation of Pd nanoparticles within MOFs for enhancing low-temperature activity towards DCPD hydrogenation

Precise control of the local environment and electronic state of the guest is an important method of controlling catalytic activity and reaction pathways.In this paper,guest Pd NPs were introduced into a series of host UiO-67 MOFs with different functional ligands and metal nodes,the microenvironment and local electronic structure of Pd is modulated by introducing bipyridine groups and changing metal nodes(Ce_(6)O_(6) or Zr_(6)O_(6)).The bipyridine groups not only promoted the dispersion Pd NPs,but also facilitated electron transfer between Pd and UiO-67 MOFs through the formation of Pd-N bridges.Compared with Zr6 clusters,the tunability and orbital hybridisation of the 4f electronic structure in the Ce_(6) clusters modulate the electronic structure of Pd through the construction of the Ce-O-Pd interfaces.The optimal catalyst Pd/UiO-67(Ce)-bpy presented excellent low-temperature activity towards dicyclopentadiene hydrogenation with a conversion of>99% and a selectivity of>99%(50℃,10 bar).The results show that the synergy of Ce-O-Pd and Pd-N promotes the formation of active Pd^(δ+),which not only enhances the adsorption of H_(2) and electron-rich C=C bonds,but also contributes to the reduction of proton migration distance and improves proton utilization efficiency.These results provide valuable insights for investigating the regulatory role of the host MOFs,the nature of host-guest interactions,and their correlation with catalytic performance.

Kinetics insights into size effects of carbon nanotubes'growth and their supported platinum catalysts for 4,6-dinitroresorcinol hydrogenation

Size effects are a well-documented phenomenon in heterogeneous catalysis,typically attributed to alterations in geometric and electronic properties.In this study,we investigate the influence of catalyst size in the preparation of carbon nanotube(CNT)and the hydrogenation of 4,6-dinitroresorcinol(DNR)using Fe_(2)O_(3)and Pt catalysts,respectively.Various Fe_(2)O_(3)/Al_(2)O_(3)catalysts were synthesized for CNT growth through catalytic chemical vapor deposition.Our findings reveal a significant influence of Fe_(2)O_(3)nanoparticle size on the structure and yield of CNT.Specifically,CNT produced with Fe_(2)O_(3)/Al_(2)O_(3)containing 28%(mass)Fe loading exhibits abundant surface defects,an increased area for metal-particle immobilization,and a high carbon yield.This makes it a promising candidate for DNR hydrogenation.Utilizing this catalyst support,we further investigate the size effects of Pt nanoparticles on DNR hydrogenation.Larger Pt catalysts demonstrate a preference for 4,6-diaminoresorcinol generation at(100)sites,whereas smaller Pt catalysts are more susceptible to electronic properties.The kinetics insights obtained from this study have the potential to pave the way for the development of more efficient catalysts for both CNT synthesis and DNR hydrogenation.

P-induced electron transfer interaction for enhanced selective hydrogenation rearrangement of furfural to cyclopentanone

Optimizing the intrinsic activity of non-noble metal by precisely tailoring electronic structure offers an appealing way to construct cost-effective catalysts for selective biomass valorization.Herein,we reported a P-doping bifunctional catalyst(Ni-P/mSiO_(2))that achieved 96.6%yield for the hydrogenation rearrangement of furfural to cyclopentanone at mild conditions(1 MPaH_(2),150°C).The turnover frequency of Ni-P/mSiO_(2)was 411.9 h^(-1),which was 3.2-fold than that of Ni/mSiO_(2)(127.2 h^(-1)).Detailed characterizations and differential charge density calculations revealed that the electron-deficient Niδ+species were generated by the electron transfer from Ni to P,which promoted the ring rearrangement reaction.Density functional theory calculations illustrated that the presence of P atoms endowed furfural tilted adsorb on the Ni surface by the C=O group and facilitated the desorption of cyclopentanone.This work unraveled the connection between the localized electronic structures and the catalytic properties,so as to provide a promising reference for designing advanced catalysts for biomass valorization.

Inclusion of CoTiO_(3) to ameliorate the re/dehydrogenation properties of the Mg–Na–Al system

For the first time,the MgH_(2)–NaAlH_(4)(ratio 4:1)destabilized system with CoTiO_(3) addition has been explored.The CoTiO_(3)-doped MgH_(2)–NaAlH_(4) sample begins to dehydrogenate at 130℃,which is declined by 40℃ compared to the undoped MgH_(2)–NaAlH_(4).Moreover,the de/rehydrogenation kinetics characteristics of the CoTiO_(3)-doped MgH_(2)–NaAlH_(4) were greatly ameliorated.With the inclusion of CoTiO_(3),the MgH_(2)–NaAlH_(4) composite absorbed 5.2 wt.%H_(2),higher than undoped MgH_(2)–NaAlH_(4).In the context of dehydrogenation,the CoTiO_(3)-doped MgH_(2)–NaAlH_(4) sample desorbed 2.6 wt.%H_(2),almost doubled compared to the amount of hydrogen desorbed from the undoped MgH_(2)–NaAlH_(4) sample.The activation energy obtained by the Kissinger analysis for MgH_(2) decomposition was significantly lower by 35.9 kJ/mol than the undoped MgH_(2)–NaAlH_(4) sample.The reaction mechanism demonstrated that new phases of MgCo and AlTi_(3) were generated in situ during the heating process and are likely to play a substantial catalytic function and be useful in ameliorating the de/rehydrogenation properties of the destabilized MgH_(2)–NaAlH_(4) system with the inclusion of CoTiO_(3).

Enhanced bimetallic CuCo nanoparticles on nitrogen-doped carbon for selective hydrogenation of furfural to furfuryl alcohol through strong electronic interactions

Bimetallic CuCo catalysts with different Cu to Co ratios on N-doped porous carbon materials(N-C)were achieved using impregnation method and applied in the hydrogenation of furfural(FAL)to furfuryl alcohol(FOL).The high hydrogenation activity of FAL over Cu_(1)Co_(1)/N-C was originated from the synergistic interactions of Cu and Co species,where Co^(0)and Cu^(0)simultaneously adsorb and activate H_(2),and Cu^(+) served as Lewis acid sites to activate C]O.Meanwhile,electrons transfer from Cu to Co promoted the formation of Cu^(+).In situ Fourier transform infrared spectroscopy analysis indicated that Cu_(1)Co_(1)/N-C adsorbed FAL with a tilted η^(1)-(O)configuration.The superior Cu_(1)Co_(1)/N-C showed excellent adsorbed ability towards H_(2) and FAL,but weak adsorption for FOL.Therefore,Cu_(1)Co_(1)/N-C possessed 93.1%FAL conversion and 99.0% FOL selectivity after 5 h reaction,which also exhibited satisfactory reusability in FAL hydrogenation for five cycles.

Silica-modified Pt/TiO_(2) catalysts with tunable suppression of strong metal-support interaction for cinnamaldehyde hydrogenation

Tuning Strong Metal-support Interactions(SMSI)is a key strategy to obtain highly active catalysts,but conventional methods usually enable TiO_(x) encapsulation of noble metal components to minimize the exposure of noble metals.This study demonstrates a catalyst preparation method to modulate a weak encapsulation of Pt metal nanoparticles(NPs)with the supported TiO_(2),achieving the moderate suppression of SMSI effects.The introduction of silica inhibits this encapsulation,as reflected in the characterization results such as XPS and HRTEM,while the Ti^(4+) to Ti^(3+) conversion due to SMSI can still be found on the support surface.Furthermore,the hydrogenation of cinnamaldehyde(CAL)as a probe reaction revealed that once this encapsulation behavior was suppressed,the adsorption capacity of the catalyst for small molecules like H_(2) and CO was enhanced,which thereby improved the catalytic activity and facilitated the hydrogenation of CAL.Meanwhile,the introduction of SiO_(2) also changed the surface structure of the catalyst,which inhibited the occurrence of the acetal reaction and improved the conversion efficiency of C=O and C=C hydrogenation.Systematic manipulation of SMSI formation and its consequence on the performance in catalytic hydrogenation reactions are discussed.

Towards the insights into the deactivation behavior of acetylene hydrogenation catalyst

A series of model catalysts were obtained by treating commercial fresh and spent catalysts unloaded from the factory with different methods, including green oil dipping, extraction and high-temperature regeneration;finally, the deactivation behavior of the commercial catalyst for acetylene hydrogenation were studied. The influence of various possible deactivation factors on the catalytic performance was elucidated via detailed structural characterization, surface composition analysis, and activity evaluation.The results showed that green oil, carbon deposit and sintering of active metal were the main reasons for deactivation, among which green oil and carbon deposit led to rapid deactivation, while the activity could be recovered after regeneration by high-temperature calcination. The sintering of active metal components was attributed to the high-temperature regeneration in hydrothermal conditions, which was slow but irreversible and accounted for permanent deactivation. Thus, optimizing the regeneration is expected to extend the service life of the commercial catalyst.

Effect of Different Morphologies Induced by Solvent on ZIF-67 Derived Co@NC for Catalytic Phenol Hydrogenation

The Co@NC catalysts with different morphologies were prepared by two step process,solvent control growth and pyrolysis method.The polyhedral Co@NC-67P-450 catalyst has a relatively high CoNx content and exhibits excellent phenol hydrogenation activity(conversion 96.9%)at 160℃,3 MPa,which is higher than that of leaf shaped Co@NC-67L-450 catalyst(conversion 75.4%).We demonstrated Co_(3)O_(4)was reduced to the Co^(0)during the reaction.Moreover,CoNx species contribute to the superior hydrogenation activity of phenol.The Co-based catalysts can be easily recovered through the magnetic separation and performed the high stability.

Effect of Fe Addition on Dehydrogenation Performance of Methylcyclohexance over Pt/Al_(2)O_(3)

Catalysts with varying Fe contents were prepared using a sequential impregnation method to investigate the effects of Fe addition on the physicochemical properties of Pt/Al_(2)O_(3) and their performance in methylcyclohexane(MCH)dehydrogenation.The results demonstrated that the addition of Fe to Pt/Al_(2)O_(3) enhanced the electron density of Pt and improved catalytic activity,while exhibiting negligible influence on the catalytic selectivity for toluene.When the Fe content was 0.057%,the catalyst exhibited the highest MCH consumption rate,which was approximately two times higher than that of the catalyst without Fe.Additionally,the incorporation of Fe inhibited the formation of coke and reduced the quantity of coke deposits on the catalyst,thereby improving its catalytic durability.Overall,Fe shows promise as a prospective secondary element for Pt/Al_(2)O_(3) to enhance the MCH dehydrogenation performance.

MOF-assisted Synthesis of Dual-atom Palladium Catalysts for Acetylene Semi-hydrogenation

The selective removal of trace acetylene in ethylene feed gas is of great significance in the petrochemicalindustry;however, there are still challenges in designing and developing high-performance catalysts. Here, a MOFassistedencapsulation strategy was adopted for the precise synthesis of diatomic Pd2 sites on a ZnO support. When usedfor the acetylene semi-hydrogenation reaction, the dual-atom Pd2-ZnO catalyst exhibited improved catalytic performance,achieving complete conversion of acetylene at 125 °C with an 89% selectivity to ethene, as compared to Pd single-atom andnanoparticles. This enhancement was mainly attributed to the catalyst’s ability to dissociate H2 and facilitate the desorptionof intermediate C2H4. Moreover, the strong interaction between the support and the diatomic Pd sites was responsible for thecatalyst’s excellent stability during the long-term reaction.

Pd^(0)-O v-Ce^(3+) Interfacial Sites with Charge Redistribution for Enhanced Hydrogenation of Methyl Oleate to Methyl Stearate

Improving the efficiency of metal/reducible metal oxide interfacial sites for hydrogenation reactions of unsaturated groups(e.g.,C=C and C=O)is a promising yet challenging endeavor.In our study,we developed a Pd/CeO_(2) catalyst by enhancing the oxygen vacancy(O V)concentration in CeO_(2) through high-temperature treatment.This process led to the formation of an interface structure ideal for supporting the hydrogenation of methyl oleate to methyl stearate.Specifi cally,metal Pd^(0) atoms bonded to the O V in defective CeO_(2) formed Pd^(0)-O v-Ce^(3+)interfacial sites,enabling strong electron transfer from CeO_(2) to Pd.The interfacial sites exhibit a synergistic adsorption eff ect on the reaction substrate.Pd^(0) sites promote the adsorption and activation of C=C bonds,while O V preferably adsorbs C=O bonds,mitigating competition with C=C bonds for Pd^(0) adsorption sites.This synergy ensures rapid C=C bond activation and accelerates the attack of active H*species on the semi-hydrogenated intermediate.As a result,our Pd/CeO_(2)-500 catalyst,enriched with Pd^(0)-O v-Ce^(3+)interfacial sites,dem-onstrated excellent hydrogenation activity at just 30℃.The catalyst achieved a Cis-C18:1 conversion rate of 99.8% and a methyl stearate formation rate of 5.7 mol/(h·g metal).This work revealed the interfacial sites for enhanced hydrogenation reactions and provided ideas for designing highly active hydrogenation catalysts.