High Activity Of Catalyst Research Articles

Promoting effect of polyoxometallic acid modification on the NH3-SCR performance of Mn-based catalysts

The strong oxidation capabilities of Mn sites render Mn-based catalysts showing high activities of selective catalytic reduction (SCR) at temperatures < 250℃, but simultaneously lead to the generation of by-product N2O with strong greenhouse effect. The activity-N2-selectivity trade-off was a prevalent observation in the development of Mn-based SCR catalysts. Here, a polyoxometallic acid enhancement strategy was devised to simultaneously promote the N2 selectivity and low-temperature SCR (LT-SCR) activity of Mn-based metal oxide catalysts, where the introduction of uniformly dispersed phosphomolybdic acid (HPMo) tuned the oxidation capabilities and enhanced NH3 adsorption-storage capability of catalysts. The combination of transient reaction, in-situ DRIFTS analysis and DFT calculations revealed that the main origin of N2O on the Mn-based catalysts was the deep oxidation of NH3, which was inhibited by the interaction between HPMo and Mn sites. Additional NH3 molecules adsorbed by the abundant acid sites supplied by HPMo further facilitated the SCR reaction. This strategy could guide the design of high-activity and high-selectivity LT-SCR catalysts for industrial denitration.

Tailoring Li2CO3 configuration and orbital structure of CoS to improve catalytic activity and stability for Li‐CO2 batteries

AbstractThe sluggish reaction kinetics has greatly hampered the development of reversible Li‐CO2 batteries. Especially during charge, high charge voltage and possible side reactions during Li2CO3 decomposition require both high activity and strong durability of catalysts. Herein, a strategy of introducing rich sulfur vacancies is proposed, which tailors the configuration of Li2CO3 and the orbital structure of CoS to realize the dual enhancement. The calculation results show that charge redistribution by sulfur vacancies on the catalyst stretches the adsorbed Li2CO3 and consequently facilitates its decomposition. Moreover, the induced vacancies lower the S 2p band center, promoting the electrochemical stability of sulfides. Therefore, Li‐CO2 batteries with sulfur vacancy‐rich CoS exhibit a low overpotential of 1.07 V after 400 h cycling, while batteries with pristine CoS have a short lifespan that the overpotential exceeds 1.75 V after cycling for 200 h. This study not only proposes a strategy to improve both catalytic activity and stability but also paves new avenues for designing advanced catalysts for Li‐CO2 batteries and beyond.image

Efficiency NiCu/t-zirconia catalysts for methanol steam reforming: Experimental and DFT insights

The development of copper-based catalysts with superior stability, activity, and reduced CO selectivity has been a prominent subject of research in the domain of hydrogen production via methanol steam reforming. In this paper, the bimetallic Ni–Cu catalysts supported by t-ZrO2 were synthesized, with varying concentrations of copper phase being considered. The prepared catalysts were characterized by XRD, XPS, BET, ICP, FESEM, TEM, H2-TPR, EPR and N2O titration, and the results showed that appropriate copper phase concentration and nickel doping obviously decreased the crystal size and promoted the development of pore structure. With the condition of W/M = 3 and LHSV = 5.6 h−1, the catalytic activity revealed the methanol conversion and H2 yield of CNZs were evaluated. The CNZ-4 exhibited optimal performance and stability in the MSR process, with a methanol conversion rate of 100 % and H2 yield of 311 mmol g−1 h−1 at a temperature of 533 K. Given the results that in-situ DRIFTS tests showed, the generation of methyl formate as an intermediate was evaluated. Moreover, further DFT insights pointed out that the ternary surface model showed the best surface adsorption and reaction performance, which provided evidence for the high activity of CNZ catalyst at the molecular level.

Multi-vacancy synergistic effect in a NiSe0.4S1.6/ZnO heterostructure for promoting photocatalytic hydrogen production

Defect engineering is one of the methods to improve catalytic activity of photocatalysts, but there are few reports on multi-vacancy systems. In this paper, S doping NiSe2 (NiSe0.4S1.6, NSS) was synthesized and further the NSS/xZnO heterostructures containing Ni, Se and O vacancies were constructed. The hydrogen and active oxygen ions are in situ generated at oxygen vacancy (VO) in ZnO, which greatly reduce the recombination of photocarriers, and the generated active oxygen ions and sacrificial agent anions (S2−, SO32−) involve in the regeneration of oxygen vacancy, which may be one of the reasons for the high activity and stability of the composite catalysts. The polarization electric field is formed by regulating the selenium and nickel double vacancy (VSe, VNi) generated by doping NiSe2 with S, which further improves the charge separation leading to the promotion of photocatalytic hydrogen production. The synergistic effect of the three types of vacancies and the redox properties of the composite catalyst lead to a high H2 production rate of 17.04 mmol·g−1·h−1, 54 and 76 times higher than NSS and ZnO, and a high apparent quantum yield of 15.30 % at 400 nm. The hydrogen production mechanism was explored by EPR, Mott-Schottky, VB-XPS, in suit XPS, DFT, etc. This work proves that the combination of transition metal oxides with rich oxygen defects and metal chalcogenides with metal and chalcogen di-vacancies containing local polarized electric fields is an effective strategy to design high active photocatalyts for water splitting.

Green preparation of fiberboard waste derived N–doped carbon catalysts with tailored properties for efficient hydrogenation reduction of nitroaromatics

Biomass–derived carbon materials doped with diverse heteroatoms have demonstrated huge potentials for environment and energy applications, thanks to the availability, preferable porous and channel structures, and excellent conductivity and stability. In this work, fiberboard waste containing resin–based adhesive was selected for the green fabrication of N–doped carbon catalysts without using extra N–sources. A facile two–step calcination strategy with sequential carbonization and activation was proposed for generation and exposure of indispensable active sites, realizing the controllable regulation of textural and morphological characteristics. The resulting N–doped fiberboard derived carbon (NFC) samples possessed unique hierarchically porous structures with a significantly enlarged surface area, plentiful activity–dependent N species (e.g., graphitic N and pyridinic N), as well as suitable graphitization degree and surface hydrophilicity. As a result, a favorable adsorption procedure and an enhanced accessibility of active sites synergistically boosted the catalytic performance towards hydrogenation reduction of nitroaromatics. Taking the NFC–hh sample as paradigm, an excellent performance was demonstrated for 4–nitrophenol (4–NP) reduction, achieving a high apparent rate constant of 0.40 min−1 and an impressive turnover frequency of ∼0.20 mmol g−1 min−1. Besides, the continuous–flowing catalytic test exhibited an excellent conversion efficiency > 99.50% with a long–term stability over 100 h, showing an attractive prospect for industrial application. This work presents a new approach for high value–added utilization of biomass waste, and provides a low–cost and high–active catalyst for environmental remediation.

Electron Structure Tuned Oxygen Vacancy-Rich AuPd/CeO2 for Enhancing 5-Hydroxymethylfurfural Oxidation.

The design of high activity catalyst for the efficiently conversion of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) gains great interest. The rationally tailoring of electronic structure directly affects the interaction between catalysts and organic substrates, especially molecular oxygen as the oxidant. This work, the bimetallic catalysts AuPd/CeO2 were prepared by the combining method of chemical reduction and photo-deposition, effectively concerting charge between Au and Pd and forming the electron-rich state of Au. The increasing of oxygen vacancy concentration of CeO2 by acidic treatment can facilitate the adsorption of HMF for catalysts and enhance the yield of FDCA (99.0 %). Moreover, a series of experiment results combining with density functional theory calculation illustrated that the oxidation performance of catalyst in HMF conversion was strongly related to the electronic state of interfacial Au-Pd-CeO2. Furthermore, the electron-rich state sites strengthen the adsorption and activation of molecular oxygen, greatly promoting the elimination of β-hydride for the selective oxidation of 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) to FDCA, accompanied with an outgoing FDCA formation rate of 13.21 mmol ⋅ g-1 ⋅ min-1 at 80 °C. The perception exhibited in this research could be benefit to understanding the effects of electronic state for interfacial sites and designing excellent catalysts for the oxidation of HMF.

Density functional theory-based screening of Ti4C3O2-loaded single atoms for efficient selective catalytic oxidation of formaldehyde

Indoor formaldehyde (HCHO) pollution poses a major risk to human health. Low-temperature catalytic oxidation is an effective method for HCHO removal. The high activity and selectivity of single atomic catalysts provide a possibility for the development of efficient non-precious metal catalysts. In this study, the most stable single-atom catalyst Ti–Ti4C3O2 was screened by density functional theory among many single atomic catalysts with two-dimensional (2D) monolayer Ti4C3O2 as the support. The computational results show that Ti–Ti4C3O2 is highly selective to HCHO and O2 in complex environments. The HCHO oxidation reaction pathways are proposed based on the Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms. According to the reaction energy and energy span models, the E-R mechanism has a lower maximum energy barrier and higher catalytic efficiency than the L-H mechanism. In addition, the stability of the Ti–Ti4C3O2 structure and active center was verified by diffusion energy barrier and ab initio molecular dynamics simulations. The above results indicate that Ti–Ti4C3O2 is a promising non-precious metal catalyst. The present study provides detailed theoretical insights into the catalytic oxidation of HCHO by Ti–Ti4C3O2, as well as an idea for the development of efficient non-precious metal catalysts based on 2D materials.

Methane dehydroaromatization over Mo/H-ZSM-5: A comparative study of the regeneration methods

The catalytic activity and deactivation characteristic of spherically shaped Mo/H-ZSM-5 particles in the non-oxidative dehydroaromatization of methane was evaluated in a fluidized bed reactor under different cyclic reaction-regeneration operation modes. The aim is to verify the superiority of the H2 regeneration approach over that oxidative approach in restoring the catalytic performance of coke-deactivated Mo/H-ZSM-5 catalyst. Compared with the fresh catalyst, the catalyst samples oxidatively regenerated at 973 and 1073 K exhibited at 1073 K a largely reduced initial activity and an obviously accelerated deactivation rate. By contrast, the catalyst sample regenerated in a H2 stream at 1073 K maintained basically the initial activity level and deactivation characteristic of the fresh catalyst over cycles. Oxidatively regenerated at a lower temperature of 773 K, the catalyst sample was allowed to maintain the initial high activity of the fresh catalyst but its deactivation rate estimated over a 20 min reaction period showed an obvious tendency to increase with increasing the number of regeneration cycles. Characterization of all spent catalyst samples using TG, XRD and NMR techniques revealed that a significant loss of active Mo sites via sublimation and/or formation of inactive Al2(MoO4)3 and local collapse of zeolite framework occurred to the two samples once oxidatively regenerated at 973 and 1073 K, while neither Mo loss nor framework breakdown was detected with the H2-regenerated sample. Additionally, the formation of disordered non-framework Al was found to occur to the two samples once oxidatively regenerated at 773 and 873 K. All these suggest that applying the H2 approach to regenerate coke-deactivated Mo/H-ZSM-5 enables the catalyst to avoid losing any of its active Mo sites in its cyclic regeneration process and therefore must be helpful for maintenance of its catalytic performance over the reaction-regeneration cycles.

Well-defined ternary metal phosphide nanowires with stabilized Pt nanoclusters to boost alkaline hydrogen evolution reaction

Designing low-content and high-activity Pt-based catalysts with the high durability for the electrochemical hydrogen production remains a challenge. In this study, a ternary metal phosphide (NiCoP) with 1D nanowire (NW) and 2D nanosheet (NS) morphologies incorporating Pt clusters (denoted as Ptcluster-NiCoP@NF NWs and Ptcluster-NiCoP@NF NSs, respectively) was prepared using a hydrothermal–phosphorization–electrodeposition method. Based on the “tip effect” of NWs and a high electrochemical surface area, the as-prepared Ptcluster-NiCoP@NF NWs display better hydrogen evolution reaction (HER) performance, with a low overpotential of 65 mV at a high current density of 100 mA cm−2 and a low Tafel slope of 38.86 mV dec−1, than the Ptcluster-NiCoP@NF NSs, with an overportential of 95 mV at 42.53 mV dec−1. This indicates that the NiCoP NW-based support exhibits faster HER kinetics. The mass activity (11.47 A mgPt−1) of the Ptcluster-NiCoP@NF NWs is higher than that of commercial Pt/C catalysts. Significantly, the Ptcluster-NiCoP@NF NWs display excellent cyclic stability with negligible losses for 5000 cycles and 30-h tests at a high current of 500 mA cm−2.

CO2 Hydrogenation to CH3OH on Metal-Doped TiO2(110): Mechanisms, Strain Effect and a New Thermodynamic-Kinetic Relation.

Surface strain and linear thermodynamic-kinetic relation are interesting topics in catalysis. Development of low temperature methanol catalysts of high activity and selectivity is of particularly importance for conversion of CO2 to methanol. In the present paper CO2 hydrogenation to methanol on Znx@TiO2(110) (x=0-2) was explored using density functional calculations and microkinetic simulations. The reaction mechanisms on the three model systems were determined and it is shown that Zn2@TiO2(110) is the most active. The most favorable pathway on Zn2@TiO2(110) is identified and CO2+H to HCOO is found to be the rate-controlling step. It is demonstrated that there is a linear relation (named AEB relation) between the adsorption energies of the initial states and the barriers for the controlling step on the 18 systems studied. Calculations on strained surfaces show that the AEB relation exists within ±1 % strain. Sr2@TiO2(110) and -1 % strained CaZn and ZnCu doped TiO2(110) are potential good low temperature catalysts and deserve experimental testing.

Ceria-modified palladium-based catalysts as high-performance electrocatalysts for oxygen reduction and formic acid oxidation

Recently, a primary challenge hindering the commercialization of direct fuel cells is the development of robust nonplatinum electrocatalysts to improve the performance of the oxygen reduction reaction (ORR) and formic acid oxidation reaction (FAOR). In this paper, polyol reduction and high temperature calcination carbonization were used to improve the conductivity of the catalyst by the modification of rare earth Ce. Pd has similar properties to Pt, with one-fifth of the properties of Pt, and the rare earth elements have low electronegativity, making it easy to supply electrons and fill Pd's antibonding orbitals. Rare Earth elements effectively enhance ORR activity by making palladium more metallic. The high-activity, low-cost and high-stability electrocatalytic ORR and FAOR catalysts PdxCe/C were designed. After a series of testing methods, the physical properties and electrochemical properties were characterized, and the optimum structure and composition were selected. The stability of the catalyst with the optimal structure and composition was assessed, and it was applied to various composite batteries to verify its capability in practical application.

High Active Catalyst of the Cu–Ag Bimetal Supported on Defect KTaO3 Nanosheets for the Selective Hydrogenation of Cinnamaldehyde to Cinnamyl Alcohol

High Active Catalyst of the Cu–Ag Bimetal Supported on Defect KTaO₃ Nanosheets for the Selective Hydrogenation of Cinnamaldehyde to Cinnamyl Alcohol

Multiscale nanoengineering fabrication of air electrode catalysts in rechargeable Zn-air batteries

The development of cost-effective, high-activity and stable catalysts to accelerate the sluggish kinetics of cathodic oxygen reduction/evolution reactions (ORR/OER) plays a critical part in commercialization application of rechargeable Zn-air batteries (RZABs). Herein, a multiscale nanoengineering strategy is developed to simultaneously stabilize Co-doped Fe nanoparticles originated from metal-organic framework-derived approach and atomic Fe/Co sites derived from metal nanoparticle-atomized way on N-doped hierarchically tubular porous carbon substrate. Thereinto, metal nanoparticles and single atoms are respectively used to expedite the OER and ORR. Consequently, the final material is acted as an oxygen electrode catalyst, displaying 0.684 V of OER/ORR potential gap, 260 mW cm-2 of peak power density for liquid-state RZAB, 110 mW cm-2 of peak power density for solid-state RZAB, and 1000 charge-discharge cycles without decay, which confirms great potential for energy storage and conversion applications.

Facile synthesis of CoFeAl-layered double hydroxides activated by peroxymonosulfate for enhanced ciprofloxacin degradation

Advanced oxidation processes (AOPs) have consistently attracted interest in the treatment of pharmaceutical pollutants. However, certain AOPs such as peroxymonosulfate (PMS) activation require effective catalysts for enhanced pollutant degradation. Herein, we have engineered a CoFeAl-layered double hydroxide (LDH) catalyst that is reliable and efficient. The objective of this project was to initiate the use of PMS to break down ciprofloxacin (CIP), thus addressing the problem of pharmaceutical contamination. CoFeAl-LDH catalysts were prepared using different high-temperature sintering times, and their catalytic performance and efficiency were observed. In a duration of 60 min, the CIP decomposition rate was found to be 91.4%, accompanied by a removal rate constant (Kobs) of 0.036 min−1; this indicates the high activity and efficiency of the CoFeAl-LDH catalyst. The catalyst additionally showcased a substantial specific surface area and exceptional recyclability, thereby offering valuable understanding into the mechanisms of activation and degradation, and positioning it as a potential contender for applications in pollutant treatment.

A novel CeO2 nanowire catalyst prepared by the freeze-drying method with significantly improved catalytic performance for toluene oxidation

A wire like CeO2 catalyst (CeO2-w) was obtained after the calcination of the precursor at 400 °C, which was prepared by the freeze-drying method for the first time. It shows good performance for catalytic oxidation of toluene with T90 of 220 °C, which is much better than the CeO2 catalysts with other structures prepared by the different methods. The good performance of CeO2-w is due to the bigger pore volume, more active oxygen species, more oxygen vacancies, better low temperature reducibility, higher surface area normalized reaction rates and lower Ea value. Additionally, the CeO2-w catalyst exhibits good water resistance and catalyst stability. In situ DRIFTS indicates the catalytic oxidation of toluene on CeO2-w undergoes the progress of toluene → benzaldehyde → benzoic acid → maleic acid → CO2 and H2O. This work affords a new idea to prepare high active CeO2 nanowire catalysts for catalytic oxidation of toluene, and open an efficient way for the construction of CeO2 based composite catalysts for VOCs degradation.

Research on preparation of high activity and durable carbon-supported platinum catalyst for methanol electro-oxidation by a facile continuous microwave pipeline method

In methanol oxidation reaction (MOR), it is crucial for the catalyst that Pt particles uniformly cover the surface of the carrier and the Pt surface active sites can effectively remove the binding with CO. This article develops a simple and effective continuous microwave technology. Carbon loaded nano platinum was synthesized by rapidly and uniformly heating a ethylene glycol mixture containing carbon black (CB) H2PtCl6 using microwave radiation, with a Pt content of 49.5%. The experimental results indicate that platinum particles are uniformly loaded onto the carbon surface, with uniform shape and size, and an average particle size of 3.02 nm. And the Pt/C catalyst prepared by continuous microwave technology showed enhanced electrocatalytic activity (peak current density of 76.95 mA/cm2) in MOR after heating at appropriate temperature in N2 atmosphere, which exceeded the commercial catalyst TKK (47.07 mA/cm2) by 63.6%. And the catalyst's resistance to CO toxicity and durability; Higher than commercial Pt/C catalysts. Compared with traditional methods, continuous microwave technology exhibits higher energy utilization efficiency and faster reaction speed in the catalyst preparation process. This technology also has the ability to achieve continuous preparation, which is one of the effective technological approaches to achieve large-scale catalysts production.

Ni/Fe Bimetallic Atom Cluster Activate PMS To Promote 1O2 Production To Efficiently Remove BPA

AbstractThe advanced oxidation process based on peroxymonosulfate (PMS) is a new water purification strategy. In this work, Ni/Fe bimetallic atom cluster composite catalyst is prepared by a hydrothermal synthesis to stimulate PMS to produce high concentration singlet oxygen (1O2) and efficiently remove bisphenol A (BPA) from aqueous solution. The experimental data show that in a broad pH range (pH=3–11), the removal rate of BPA by the non‐free radical pathway induced by 1O2 is close to 100 %, and the catalyst still has high stability after 5 cycles. The mechanism of BPA removal in NiFe−BC/PMS/BPA catalytic degradation system is investigated by quenching experiment. It is found that 1O2 in the system is the most important active component in the degradation process of BPA, and a high concentration of 1O2 could promote the rapid degradation of BPA in solution. In this paper, the high catalytic activity and selectivity of bimetallic atomic cluster catalysts can provide new insights for the treatment of phenolic wastewater.

Effects of Co3C formation on the catalytic performance for Fischer-Tropsch synthesis over Co/SiO2 catalysts

Cobalt carbides demonstrate higher selectivity towards light olefins and alcohols in the Fischer-Tropsch synthesis (FTS). In this study, we present an investigation of a series of supported cobalt catalysts that were carburized with CO for different time. The presence of Co3CCo, Co and Co2CCo phases in these catalysts was confirmed through Transmission Electron Microscopy (TEM). The Co/SiO2-RC-0.5 h catalyst with both Co3C and Co structure exhibits the highest CO conversion for the FTS reaction. By utilizing the chemisorption techniques, we studied the structure-performance relationships between the phase and activity, and confirmed that Co3C has the highest intrinsic activity, which is beneficial for CO activation. This study provides further insight into the positive effects of Co3C on the FTS reaction and guides us in the rational design of high active Co-based FTS catalysts.

Single Atom Ru Doped Ni2P/Fe3P Heterostructure for Boosting Hydrogen Evolution for Water Splitting.

Modulating the chemical composition and structure has been considered as one of the most promising strategies for developing high-efficient water splitting catalysts. Here, a single-atom Ru doped Ni2P/Fe3P catalyst is synthesized by introducing the dispersed Ru atoms to adjust Ni2P/Fe3P heterostructure. Single atom Ru provides effective hydrogen evolution reaction (HER) active sites for boosting catalytic activities. The catalyst with only 0.2wt.% content of Ru exhibits an overpotential of 19.3mV at 10mA cm-2, which is obviously lower than 146.1mV of Ni2P/Fe3P. Notably, an alkaline overall water electrolyzer based on Ru-Ni2P/Fe3P catalysts achieves a cell voltage of 1.47V and operates over 600h at 10mA cm-2, which is superior to that of benchmark RuO2//Pt/C (1.61V). The theoretical calculations further confirm that Ru single atom doping can effectively optimize the hydrogen/water adsorption free energy of the active site and therefore improve the HER activity of heterostructure. This work provides a valuable reference to design high-activity and durability catalyst for water splitting through the double modulation of interface-effect and atomic doping.

Experimental study on modified lotus stem biochar-based catalysts for heavy oil aquathermolysis

To obtain high-activity catalysts for aquathermolysis at low temperatures, a composite modification method of KOH and silane coupling agent KH570 was used to successfully prepare modified lotus stem biochar (MLSB), and six catalysts with different ZrO2 and MoO3 contents (5–30 %) were synthesized by impregnation method. MLSB and catalysts were analyzed by SEM, N2 adsorption and desorption isotherms, surface pore size, and FT-IR. The results revealed that the pores of raw lotus stem biochar were increased and enlarged, and some -OH on the surface was replaced by hydrophobic groups to form hydrophobic supports. Catalysts had hydrophobic and strong acidic sites. The catalytic activities were evaluated by aquathermolysis experiments. Catalysts exhibited satisfying abilities to catalyze aquathermolysis at low temperatures (130–200 °C). Specifically, 25 % ZrO2−MoO3/MLSB catalyst displayed the optimal heavy oil viscosity reduction rate (86.1 %) at 200 °C, which was attributed to hydrophobicity, more active components and strong acid sites. The highest viscosity reduction rate of heavy oil was obtained with 25 % ZrO2−MoO3/MLSB at 200 °C and a catalyst content of 3 wt%. Continuing to increase the catalyst content decreased the viscosity reduction rate, likely due to catalyst agglomeration hindering the contact between the active component and heavy oil. Moreover, the viscosity reduction effect of the catalyst increased with higher reaction temperatures. Additionally, a reaction network of aquathermolysis catalyzed by ZrO2−MoO3/MLSB was proposed. These findings contribute to the development of efficient catalytic systems for aquathermolysis and provide insights into the application of biochar-based catalysts in heavy oil viscosity reduction.