Phase Catalytic Reaction Research Articles

Synthesis and characterization of hydrophobic nickel catalyst supported on different oxides for continuous liquid phase catalytic exchange reaction

Hydrophobic Ni catalysts supported on three metal oxides coated with PTFE namely Ni/SiO2/PTFE, Ni/Cr2O3/PTFE, and Ni/Al2O3/PTFE were used in liquid-phase catalytic exchange (LPCE) reactions to enrich hydrogen isotope and produce deuterium oxide (heavy water). Wet impregnation method was employed to prepare the Ni/SiO2, Ni/Cr2O3, and Ni/Al2O3 before PTFE coating. The as prepared catalysts were characterized using different characterization techniques and their performances were evaluated in LPCE reaction using a continuous reactor. The performance evaluation based on the D2O yield can be ranked as Ni/Al2O3/PTFE > Ni/Cr2O3/PTFE > Ni/SiO2/PTFE > Ni/PTFE. The catalysts’ performances are strongly associated with the crystallite size, particle size, hydrophobicity, surface area, pore size, and metal-support interaction. Since isotope exchange requires a dry catalyst surface, the catalyst’s hydrophobicity plays a crucial role. In addition, the catalyst support improves the LPCE reaction efficiency, as the most efficient catalyst, Ni/Al2O3/PTFE, yielded 1220 ppm D2O, compared to 520 ppm for the benchmark catalyst, Ni/PTFE. The characterization results reveal that Ni/Al2O3/PTFE outperformed the other catalysts due to its low crystallite size (D = 23.04 nm), high hydrophobicity (WCA = 139.23°), higher surface area (16.31 m2g−1), small pores (pore size = 6.18 nm), and lowest average Ni particle size (40.89 nm).

Adaptive time-step unscented kalman filtering (ATS-UKF) based observer design for urea selective catalytic reduction (SCR) performance of diesel engines

To reduce the number of sensors in the SCR catalyst, state feedback and fault diagnosis information are provided. Firstly, a model based on the coupling of flow, heat transfer, and gas-solid phase catalytic reaction in the SCR system is investigated in this paper. The parabolic partial differential equations are simplified by the variable substitution method and the method of lines approach (MOL). The simplified system of equations is solved by backward differentiation formulas (BDF) with adaptive adjustment time step strategy. Meanwhile, the chemical reaction parameters are accurately calibrated per second using the Levenberg-Marquardt method. Secondly, the ATS-UKF is designed in this paper, and to ensure the synchronisation between the ATS-UKF and the SCR model calculations, the time step of solving the BDF by the SCR model is taken as the time step of propagating the sigma points. Two observation scenarios are assumed: (1) no downstream NH3 concentration sensor, ammonia coverage and downstream NH3 concentration are observed by ATS-UKF; (2) no downstream NOx sensor, ammonia coverage and downstream NOx concentration are observed by ATS-UKF. Finally, the paper carries out bench tests. In the first case, the ammonia coverage obtained by the ATS-UKF reached 0.99 with respect to the model-calculated value R². The mean absolute error (MAE) between the observed and experimental values of the ATS-UKF for the downstream NH3 concentration was 2.76 ppm. In the second case, the ammonia coverage obtained by the ATS-UKF reached 0.99 with respect to the model-calculated value R², and the MAE between the observed and experimental values of the ATS-UKF for the downstream NOx concentration was 1.53 ppm. Environmental ImplicationThe Adaptive Time-Step Unscented Kalman Filtering (ATS-UKF) enhances urea Selective Catalytic Reduction (SCR) in diesel engines, improving environmental outcomes. This method minimizes sensor dependence, enabling more precise SCR system management and effective emission reduction. By advancing emission control technologies, ATS-UKF contributes to global air pollution mitigation efforts, supporting cleaner air and environmental sustainability. Its innovative approach in monitoring and predicting SCR performance marks a significant step towards eco-friendly diesel engine operation.

Considerations when determining Counter-diffusion constants in liquid phase catalytic reactions using the Zero Length column (ZLC) method

The confusion with diffusion: In heterogeneous catalysis often, the catalytic material is housed within a porous support structure. It is important therefore to determine whether this support structure exerts limiting behaviors. In this paper, desorption and diffusion effects are separated under reactions conditions, to provide accurate effective diffusion constants in swelling and gate-opening catalysts. • A Zero Length Column (ZLC) method was developed using liquid chromatography. • Diffusion in porous catalyst pellets as small as 5 mg can be directly characterised. • Reactant counter-diffusion coefficients were determined for the Heck reaction. • Clear differences in diffusion rates for reactants versus non-reactant species. A Zero Length Column (ZLC) method was developed using a liquid chromatographic system to calculate reactant counter-diffusion coefficients in porous, solvent swollen catalytic pellets and gate-opening support materials. Reactant diffusivities within these porous materials were determined at the reaction conditions of 80 °C and 0.3–0.75 mL min −1 . For all materials, molecules of a similar size to the pore apertures, or molecules with strong interactions with the material surfaces, catalysts, were observable by the ZLC method, with both micro and macropore diffusion observed. Differences between Pd(II) and Pd(0) forms of the EnCat30 catalyst were examined to determine the effects of catalytic deactivation. The deactivated catalyst showed iodobenzene macroporous diffusion constants similar to the relatively inert toluene molecules. Finally, pulse field gradient NMR was utilised to compare and validate ZLC diffusion measurements for solvent swollen reaction systems. This study presents much needed novel findings on diffusivity data for liquid phase catalytic systems.

Monitoring Aqueous Phase Reactions by Operando ATR‐IR Spectroscopy at High Temperature and Pressure: A Biomass Conversion Showcase

AbstractSpectroscopic insight into aqueous phase catalytic reactions under realistic conditions aids detailed understanding and fosters further improvements. However, this is also very challenging, particularly in the liquid phase, given the typically elevated temperatures and pressures employed. Here, we report an operando Attenuated Total Reflectance‐Infrared (ATR‐IR) spectroscopic method to monitor the Aqueous Phase Reforming (APR) of Kraft lignin at 225 °C and 30 bar over a Pt/Al2O3 catalyst. This is a showcase reaction, while the presented method developed is more generic. In addition to the high temperature and pressures conditions, spectral interference from bulk water is a major challenge. Other challenges include self‐absorption of IR light, molecular interactions, high substrate loadings and the noise resulting from water vapor and CO2. We present a protocol utilizing the temperature‐dependent single‐beam method to obtain high‐quality ATR‐IR spectra virtually free from temperature, background and matrix effects. The protocol allowed for effective correction for the aqueous solvent as a function of reaction temperature. A comparison with conventional spectral acquisition and correction shows the advantages of this approach.

A highly efficient and stable catalyst for liquid phase catalytic exchange of hydrogen isotopes in a microchannel reactor

The liquid phase catalytic exchange of hydrogen isotopes is a promising process for upgrading recycle water in nuclear power station. To facilitate the isotope catalytic reaction, a series of two-dimensional hydrophobic catalysts of Pt/modified carbon nitride (Pt/s-C3N4) with different Pt loadings were fabricated and applied in microchannel reactor. Their excellent catalytic performances were found in our experiments by comparing with purchased Pt/activated carbon (Pt/AC), the Turn-Over-Frequency (TOF) of Pt/s-C3N4 is 3 times higher than Pt/AC. Because the Pt clusters of 0.82 ± 0.08 nm were uniformly distributed on the support of two-dimensional carbon nitride (C3N4) to improve availability of the Pt catalyst by exposing more active sites and decreasing effect of the internal diffusion. The catalytic activity of Pt/s-C3N4 catalysts remained stable after 1800 min reaction, whereas Pt/AC displayed a 20% drop. Hydrophobicity of the catalyst maintained its high activity and stability in the liquid phase catalytic exchange reaction.

Chemistry of Trace Inorganic Elements in Coal Combustion Systems: A Century of Discovery.

Coal fueled the Industrial Revolution and the global expansion of electrification in the 20th century. In the 21st century, coal use has declined in North America and Europe, but continues to increase in Asia. Coal contains many of the elements of the Periodic Table, in percent-levels or in trace amounts (ppm, ppb). The impact of many of these elements on the environment via air and water discharges from coal-fired plants has been studied with decades of research on their chemical transformations within combustion systems and on their fates upon reintroduction into the environment. The transformations of the trace elements present in coal burned during combustion can be categorized as thermal volatilizations from the coal in the furnace; thermal decomposition of trace element compounds inside the coal; encapsulation inside ash structures through high-temperature vitrification; oxidation of the trace elements with the myriad species contained in flue gas through gas phase (homogeneous) reactions or catalytic (gas-solid) reactions; adsorption and/or reactions with active sites on entrained fly ash particulates contained in the flue gas; and absorption into solutions. These transformations can, in many cases, impact the fraction of these trace elements that are removed by various pollution control devices compared to the fraction released into the environment. The sampling and measurement of trace elements, in the inlet coal, outlet flue gas, aqueous scrubber solutions, and ash matrices, represents a significant challenge. This review focuses on the behavior of trace elements in industrial coal combustion systems with an emphasis on what has been learned over the past century uniquely related to the use of coal in boilers for electricity and heat production. Key accomplishments in measurement, modeling and control of trace element emissions in coal-fired systems are highlighted.

High NH3 selectivity of NiFe2O4 sensing electrode for potentiometric sensor at elevated temperature

NiFe2O4 was synthesized using sol-gel method for sensing electrode material of YSZ based ammonia sensor. NiFe2O4-SEs sintered at 1100 °C, 1150 °C and 1200 °C were characterized by XRD, the BET method and ESEM. By testing the NH3 response of different sensors at 650 °C, it was observed that the 1150 °C sintered sensor had the largest response value (−104.3 mV for 320 ppm NH3) and the highest sensitivity (−77.56 mV/decade), which were related to the most TPB sites and the moderate gas phase catalytic reaction. The response values of the sensor varied almost linearly with the logarithm of 20–320 ppm NH3 at 600–750 °C, which was consistent with mixed-potential mechanism testified by polarization and EIS tests. When the oxygen concentration was at 7–10 vol %, its effect on the response value was within 3%. When the water vapor concentration was 3, 6 and 9 vol %, the ammonia response value was 95.1%, 92.9% and 88.7% of the values when there was no water vapor, respectively. The sensor showed very weak cross sensitivities to NOx, but non-negligible SO2 cross sensitivity. It also displayed slight signal drifts in weekly tests in eight weeks, which showed that the sensor attached with NiFe2O4-SE has a good long-term stability.

Effects of CeVO4 electrode morphology and oxygen content on ammonia sensing properties for potentiometric sensor

The influences of sensing electrode morphology, operating temperature and the oxygen content on NH3 sensing properties for the potentiometric gas sensor attached with CeVO4 sensing electrode were studied. With the increase of electrode sintering temperature, CeVO4 grains grow up gradually. The response/recovery time shows a decreasing trend, but the NH3 sensitivity reaches the highest when the sintering temperature reaches 1000 °C, this was determined by the amount of TPB and the ammonia concentration involved in the electrode electrochemical reactions. The NH3 sensitivity enhances with the increase of operating temperature in the range of 450–550 °C and presents the mixed-potential characteristic. When the temperature exceeds 600 °C, the curve between ΔV and logarithm of NH3 concentration presents a broken line relationship, and the concentration corresponding to the inflection point increases with the increase of operating temperature. The response and recovery rates accelerate but the NH3 sensitivity decreases with the increase of oxygen content in testing gas. When the oxygen is above 10 vol.% and NH3 is below 80 ppm, the response value is almost unaffected by the change of oxygen concentration. The broken line feature of the sensitivity curve under high operating temperatures and oxygen concentrations is mainly related to the gas phase catalytic reaction of NH3 by oxygen.

Group C+ particles: Enhanced flow and fluidization of fine powders with nano-modulation

The main challenge in the flow and fluidization of Geldart Group C particles is their cohesive nature due to strong interparticle forces. The “nanoparticle modulation” technique is adopted to reduce the interparticle forces of Group C particles and thus significantly improve their flow and fluidization quality. Group C+ particles, a new type of fine particles with drastically reduced or insignificant interparticle forces, are created using the nano-modulation technique. Fundamental studies provided a comprehensive understanding of the flow and fluidization quality of Group C+ particles. Nano-modulation led to major enhancements to both the static and dynamic flowability of Group C+ particles. Moreover, Group C+ particles exhibited revolutionary advancements in fluidization, which enabled its pseudo-particulate fluidization over a wide range of operating gas velocities, up to 200–300% times that of bed expansion. The high bed expansion allows more gas to be retained in the bed and provides large volumes for gas-solid interfacial contact, thus promoting chemical reactions, especially gas phase catalytic reactions.

Synthesis of Cyclopentyl Methyl Ether by Gas Phase Catalytic Reaction Using Strong Acid Ion Exchange Resin as a Catalyst —Study of Catalyst Deactivation Mechanism—

Synthesis of Cyclopentyl Methyl Ether by Gas Phase Catalytic Reaction Using Strong Acid Ion Exchange Resin as a Catalyst —Study of Catalyst Deactivation Mechanism—

Process hazard evaluation for catalytic oxidation of 2-octanol with hydrogen peroxide using calorimetry techniques

In this work, various calorimetric and analytical techniques were implemented to identify reaction pathways and safety issues associated with the 2-octanol to 2-octanone two liquid phase catalytic reaction oxidative using aqueous hydrogen peroxide as oxidant, sodium tungstate (Na2WO4) as catalyst and methyltri-n-octylammonium hydrogen sulfate [CH3(n-C8H17)3N+HSO4−] as phase transfer catalyst. Differential scanning calorimetry (DSC) was employed to measure the temperature and heat flux of the reactant mixtures under dynamic scanning. Phi-TEC II adiabatic calorimeter was used to track temperature and pressure under worst runaway scenario. Isothermal reaction calorimeter (RC1e) was used to assess conditions relevant to normal process operations. Gas chromatography-mass spectrometry (GC–MS) was utilized to analyze final products of all measurements qualitatively and quantitatively. Data from both DSC and Phi-TEC II show that two highly exothermic reactions were detected with “onset” temperature at ~50 and ~220 °C, respectively. In all cases, only 2-octanol and 2-octanone were the identifiable compounds via GC–MS. 2-Octanol conversion was in the range of 15–50% and it reveals a linear correlation with overall heat generation. Data obtained verify that both exothermic peaks result from alcohol oxidation, thus indicating that in the conditions of the reaction and with the employed catalysts, hydrogen peroxide did not fully decompose at lower temperatures. Non-condensable gas generation measurements validated this argument. Based on those results, possible macroscopic reaction pathway was proposed. Furthermore, pressure and temperature profiles by PHI-TEC II indicated a potential transition to a homogeneous liquid phase at higher temperatures. The RC1e results verified that 2-octanol conversion was higher at higher stirring rates, while evaporative cooling of solvents tempered the reaction by removing the heat generated, thus improving safety. These findings can be further used to propose safer operating measures for design and scale-up of this reaction process to avert a potential runaway and to probe in the reaction pathways so as to increase inherently safer conditions for its performance.

Separation process study of liquid phase catalytic exchange reaction based on the Pt/C/PTFE catalysts

Abstract The liquid phase catalytic exchange (LPCE) reaction is an effective process for heavy water detritiation and production of deuterium-depleted potable water. In the current study, hydrophobic carbon-supported platinum catalysts (Pt/C/PTFE) with high efficiency as reported previously for LPCE were prepared and comprehensive performance evaluation method is applied to evaluate the separation behaviors of LPCE systematically. Experimental results indicate that the optimum reaction temperature of 60–80 °C and the molar feed ratio G/L of 1.5–2.5 would lead to higher separation efficiencies. As to the packing method, a random packing mode with a packing ratio of hydrophobic catalysts 0.25 is recommended. In addition, thermodynamic analysis corresponds well with experimental results under lower temperature and G/L, while the suppression of kinetic factors should not be neglected when T > 80 °C and G/L > 1.5.

Recent advances in metal-free carbon-based nanocatalysts

The catalytic reaction occupies an important position in the petroleum and chemical industry, and the traditional metal-based catalytic materials are hindered because of the limited reserves, poor stability, environmental pollution and so on. In recent years, with the promotion of green chemistry and sustainable chemical, metal-free carbon based nanomaterials and their applications in catalysts have attracted wide attention, and it has become a hot topic in the fields of energy, materials and chemical industry. In this paper, the relationship between the structure and catalysis of carbon-based nanomaterials is briefly introduced. When metal free carbon based materials directly used as catalysts, their catalytic active sites are mainly contain three types. Firstly, edge atoms and defect sites, whose carbon atoms are unsaturated and have high catalytic activity, can activate oxygen molecules and catalyze methane cracking. Secondly, functional groups on the surface of carbon materials. Different functional groups can catalyze different reaction systems. The oxygen-containing functional groups, for example, have certain weak acidity and they generally possess excellent catalytic performance in the acid-base reaction and multiple oxidation reactions. Thirdly, heteroatoms that replace carbon atoms into sp2 lattices will results in the changing of electron density distribution in carbon structure, which can promotion of chemical reactions by reducing the reaction energy barriers. The progress in the basic research on the application of metal-free carbon-based nanomaterials for the reaction of liquid phase, gas phase and photoelectricity in the last five years is reviewed. By in situ infrared characterization technique ( in situ FTIR) and density functional theory (DFT) calculations, the catalytic mechanism catalyzed by carbon materials was studied and the result indicates that most of the catalytic reactions are surface reactions, whose reaction rate are greatly affected by the specific surface area. The merit and demerit including, but not limited to catalytic efficient and stability of powder catalyst and monolith catalyst are list. Specially, our study shows that the construction of three-dimensional structured monolithic carbon-based catalytic materials can effectively avoid the separation problem of powder metal free carbon-based catalytic materials, and provides a reference for solving the practical bottleneck of metal free carbon-based catalytic materials in liquid phase catalytic reaction. In addition, based on the research basis of our group, the problems and future prospect of carbon-based nanomaterials are discussed from the aspect of the reaction engineering. Actually, there are few studies on the reaction engineering of metal free carbon based catalysts. At present, metal free carbon-based catalysts are mainly used in the form of ultra-fine powders. From the perspective of chemical magnification, carbon nanomaterials participate in catalytic reactions mostly in heterogeneous catalytic process, and their catalytic performance is obviously affected by catalyst dispersion, fluidity, mixed mass transfer and so on. Conventional reactors have some problems, such as weak mixing effect, blind zone of mixing, and poor inter-phase transfer effect, which lead to the contradiction between selectivity and reaction rate in the development of industrial catalytic technology of carbon nanomaterials. At the same time, there are still some problems in the traditional catalytic process, such as poor catalyst stability, easy agglomeration, and low recycling efficiency. Therefore, in order to realize the industrial scale application of metal free carbon nanomaterials catalytic reaction system, the research and development of industrial reactor suitable for the catalytic reaction process of carbon nanomaterials and its matching process is the key to form practical technology. Three-dimensional monolithic catalyst can effectively improve the efficiency of heat and mass transfer. It is expected to solve the problems of low efficiency of separation and process transfer of metal free carbon-based catalytic materials, simplify the process flow and avoid the loss of catalyst. Therefore, there is still a long way to go for the research and application of three-dimensional metal free carbon based catalysts in the future.

Suppressing Surface Lattice Oxygen Release of Li-Rich Cathode Materials via Heterostructured Spinel Li4 Mn5 O12 Coating.

Lithium-rich layered oxides with the capability to realize extraordinary capacity through anodic redox as well as classical cationic redox have spurred extensive attention. However, the oxygen-involving process inevitably leads to instability of the oxygen framework and ultimately lattice oxygen release from the surface, which incurs capacity decline, voltage fading, and poor kinetics. Herein, it is identified that this predicament can be diminished by constructing a spinel Li4 Mn5 O12 coating, which is inherently stable in the lattice framework to prevent oxygen release of the lithium-rich layered oxides at the deep delithiated state. The controlled KMnO4 oxidation strategy ensures uniform and integrated encapsulation of Li4 Mn5 O12 with structural compatibility to the layered core. With this layer suppressing oxygen release, the related phase transformation and catalytic side reaction that preferentially start from the surface are consequently hindered, as evidenced by detailed structural evolution during Li+ extraction/insertion. The heterostructure cathode exhibits highly competitive energy-storage properties including capacity retention of 83.1% after 300 cycles at 0.2 C, good voltage stability, and favorable kinetics. These results highlight the essentiality of oxygen framework stability and effectiveness of this spinel Li4 Mn5 O12 coating strategy in stabilizing the surface of lithium-rich layered oxides against lattice oxygen escaping for designing high-performance cathode materials for high-energy-density lithium-ion batteries.

Isolation, purification and characterization of a salt-active and organic-solvent-thermostable phenylalanine dehydrogenase from Bacillus nanhaiensis DSF-15A2

BackgroundAs phenylalanine dehydrogenase (EC 1.4.1.20, PheDH) activity and stability was still diminished in organic solvent and biocatalytic reaction in non-aqueous media has presented as a great alternative to chemical synthesis and biosynthesis, suggesting that it is crucial to obtain a PheDH with high organic solvent-tolerant. ResultsIt is the first case when thermo-solvent tolerant PheDH producing bacterium was isolated from a marine sample. The BnPheDH’ stability could be significantly improved by 1M NaCl, which was analyzed by molecular dynamics simulation, and it showed better stability in methanol, ethanol, ethylene glycol, ethylene glycol monoethyl ether and acetone. The kcat/Km in 30% (v/v) methanol and ethylene glycol monomethylether was 1.15- and 1.35-fold than that of in the aqueous phase, indicating that the catalytic efficiency was significantly improved by the methanol and ethylene glycol monomethylether. ConclusionsThe results indicated that the affinity of enzyme, substrate and co-factor and the catalytic efficiency can be significantly improved by organic solvents, suggesting that the BnPheDH had great application value in organic phase or aqueous-organic phase catalytic reaction, and it would be used as an robust biocatalyst to synthesize synthons in the food and pharmaceutical industries.

ChemInform Abstract: Metal‐Organic Frameworks for Catalysis

AbstractReview: 91 refs.

Metal–Organic Frameworks for Catalysis

Metal–organic frameworks (MOFs) are a relatively new class of porous material, which are comprised of metal ions or clusters linked with poly-functional organic molecules. MOFs have been studied increasingly for heterogeneous catalysis applications because these hybrid materials have well-ordered tunable porous structures with exceptional textural properties and introduction of additional active sites can be carried out easily by relatively simple post-synthesis functionalization. This short review focuses on recent works on liquid phase catalytic reactions carried out over selected MOFs. The MOF membranes for catalysis and the potential of functionalized MOF materials for chiral reactions are also mentioned briefly.

Viral Templated Palladium Nanocatalysts

AbstractPalladium (Pd) nanocatalysis plays key roles in many areas from environmental remediation, energy utilization to chemical synthesis. Viruses offer exciting opportunities and advantages as promising nanoparticle synthesis templates due to their controlled dimensions and structures, and the ability to confer precisely spaced functionalities by genetic modification to permit improved and/or tunable metal nanoparticle formation. We have utilized tubular tobacco mosaic virus (TMV) as biologically derived nanotemplates for controlled synthesis of catalytically active Pd nanoparticles. Here we describe key findings and insights gained from our studies on the synthesis and characterization, as well as on both aqueous and organic phase catalytic reactions, dichromate reduction and the Suzuki‐coupling reaction. We hope that the methodologies and results summarized here can spur further interdisciplinary collaboration, and expect that more discoveries and improved performances can be realized with future endeavors.

ChemInform Abstract: Mesoporous Materials: Versatile Supports in Heterogeneous Catalysis for Liquid Phase Catalytic Transformations

AbstractReview: 158 refs.

Method for the prediction of the particle attachment to the bubble in oil at elevated temperatures

In three phase catalytic reactions or in floatation the position of particles in respect to the gas/liquid interface is a crucial parameter affecting the efficiency of those processes. It is commonly assumed that three phase interactions are described by the contact angle, and in general the higher the contact angle the greater the probability of particle attachment to the gas/liquid interface. Contact angles are notoriously difficult to measure accurately for porous particles of wide size distribution and/or irregular shape. Also, it is practically impossible to measure the contact angles at high temperature/pressure e.g. at the conditions typical in many catalytical reactors.Here a new method, based on the thermodynamical description of interfacial/surface energies, enabling prediction of the position of particles in three phase solid/gas/liquid systems is discussed. In this method the surface energy of catalyst particles at elevated temperatures is measured using inverse gas chromatography enabling the calculation of total interaction energy between three phases and the prediction of the position of particles in gas/liquid dispersion. The predictions were in very good agreement with experimental results obtained with the bubble pick up method.