Gas-solid Catalytic Reactions Research Articles

Insight into catalytic effects of alkali metal salts addition on bamboo and cellulose pyrolysis

Alkali metal compounds have vital influence on biomass pyrolysis conversion. In this study, cellulose, and bamboo catalytic pyrolysis with different alkali metal salts catalysts (KCl, K2SO4, K2CO3, NaCl, Na2SO4, and Na2CO3) were investigated in the fixed-bed reaction system. The effects of cations (K+ and Na+) and anions (Cl-, SO42−, and CO32-) on the evolution properties of biochar, bio-oil, and gas products were explored under both in-situ and ex-situ catalytic pyrolysis. Results showed that alkali metal salts facilitated the yields of biochar and gases at the expense of that of bio-oil. Alkali metal chloride and sulfate showed a weaker catalytic effect, while alkali metal carbonate greatly promoted the generation of gas products and increased the condensation degree of biochar. With the addition of K2CO3 and Na2CO3, cyclopentanones content was over 50% from cellulose catalytic pyrolysis, and phenols content (mainly alkylphenols) reached over 80% from bamboo catalytic pyrolysis. Moreover, solid-solid catalytic reactions with K2CO3 and Na2CO3 catalysts had an important role in strikingly promoting conversion of pyrolysis products, and the solid-solid and gas-solid catalytic reactions with alkali metal carbonate catalysts were stronger than those with alkali metal chloride and sulfate catalysts. Furthermore, the possible catalytic pyrolysis mechanism of alkali metal salts on biomass pyrolysis was proposed, which is important to the high-value utilization of biomass.

Mechanistic study of integrated CO2 capture and utilization over Cu and Al-modified calcined limestone with high stability using MFB-TGA-MS

This study explores the performance of dual-functional materials (DFMs) in cyclic integrated CO2 capture and reverse water–gas shift (ICCU-RWGS) reactions under fluidized, isothermal conditions. DFMs with a copper catalyst and alumina support on calcined natural limestone were analyzed using micro-fluidized bed thermogravimetric analysis coupled with mass spectrometry (MFB-TGA-MS). The results indicate that the 10 %Cu5%Al-CaO-IMP surpasses others, demonstrating a CO2 capture capacity of 10.67 mmol⋅g−1, 71.5 % in-situ CO2 conversion at 700 °C, and remarkable cyclic stability over 30 cycles. Cu and Al additions curtail CaO agglomeration during extended ICCU-RWGS and enhance CO2 and H2 activation by removing surface formate species, promoting CO production. Furthermore, non-catalytic gas–solid reactions coexist with catalytic gas–solid reactions, leading to gradual Cu particle coating by CaCO3 during carbonation. This phenomenon prevents Cu sintering but slightly reduces catalytic activity. These findings, combined with cost-effective materials (CaO, Cu, Al), hold significant promise for efficient and economically viable ICCU processes.

Particle-scale and sub-grid drag models coupled CFD for simulating the CO methanation in a CFB riser

The diffusion and chemical reactions inside the catalyst particles and the heterogeneous flow structure in the computational cells are key factors to affect the accuracy of the coarse-grid simulation in circulating fluidized bed (CFB) methanation reactors. In this work, a particle-scale model is developed to calculate the effective reaction rate considering the transient diffusion and chemical reactions in the particle scale, i.e., the scale of the single catalyst particle. A modified sub-grid drag model is proposed to consider the effects of the meso-scale and chemical reactions on the heterogeneous gas-solid interaction, where the meso-scale is between the single particle and the whole reactor and featured with the particle cluster. Subsequently, a coupled model is developed by integrating the particle-scale and modified sub-grid drag models into CFD. Moreover, the coupled model is validated to achieve accurate predictions on the CO methanation process in a CFB riser. Notably, the coupled model can be performed with a coarse grid (∼58 times particle diameter) and a large time step (0.005 s) to accelerate the simulation. By simply changing the reaction kinetics, different gas-solid catalytic reaction systems can be simulated by using the coupled model.

Conceptual and Practical Aspects of Metal-Organic Frameworks for Solid-Gas Reactions.

The presence of site-isolated and well-defined metal sites has enabled the use of metal-organic frameworks (MOFs) as catalysts that can be rationally modulated. Because MOFs can be addressed and manipulated through molecular synthetic pathways, they are chemically similar to molecular catalysts. They are, nevertheless, solid-state materials and therefore can be thought of as privileged solid molecular catalysts that excel in applications involving gas-phase reactions. This contrasts with homogeneous catalysts, which are overwhelmingly used in the solution phase. Herein, we review theories dictating gas phase reactivity within porous solids and discuss key catalytic gas-solid reactions. We further treat theoretical aspects of diffusion within confined pores, the enrichment of adsorbates, the types of solvation spheres that a MOF might impart on adsorbates, definitions of acidity/basicity in the absence of solvent, the stabilization of reactive intermediates, and the generation and characterization of defect sites. The key catalytic reactions we discuss broadly include reductive reactions (olefin hydrogenation, semihydrogenation, and selective catalytic reduction), oxidative reactions (oxygenation of hydrocarbons, oxidative dehydrogenation, and carbon monoxide oxidation), and C-C bond forming reactions (olefin dimerization/polymerization, isomerization, and carbonylation reactions).

Singlet Oxygen and Mobile Hydroxyl Radicals Co-operating on Gas-Solid Catalytic Reaction Interfaces for Deeply Oxidizing NOx.

Learning from the important role of porphyrin-based chromophores in natural photosynthesis, a bionic photocatalytic system based on tetrakis (4-carboxyphenyl) porphyrin-coupled TiO2 was designed for photo-induced treating low-concentration NOx indoor gas (550 parts per billion), achieving a high NO removal rate of 91% and a long stability under visible-light (λ ≥ 420 nm) irradiation. Besides the great contribution of the conventional •O2- reactive species, a synergic effect between a singlet oxygen (1O2) and mobile hydroxyl radicals (•OHf) was first illustrated for removing NOx indoor gas (1O2 + 2NO → 2NO2, NO2 + •OHf → HNO3), inhibiting the production of the byproducts of NO2. This work is helpful for understanding the surface mechanism of photocatalytic NOx oxidation and provides a new perspective for the development of highly efficient air purification systems.

Investigation of microwave enhanced catalytic degradation of VOCs with a novel double ridge field compressed cavity

Volatile organic compounds (VOCs) are common organic pollutants that are harmful to human and the environment. Degradation of VOCs has aroused widespread concern. Catalytic oxidation is considered as an effective method to degrade VOCs. Microwave heating is a promising technology for heterogeneous catalytic gas–solid reactions, which is considered as an alternative to conventional conductive heating. Here, microwave enhanced catalytic degradation of VOCs were carried out in a novel double ridge field compressed cavity, in which Cu-Mn/AC catalyst was applied. The relative permittivity of Cu-Mn/AC at different temperatures were obtained by neural network. Further, based on the relative permittivity obtained, numerical simulations for the double ridge field compressed cavity were conducted at 2.45 GHz by a coupled three-dimensional electromagnetic-thermal model using COMSOL Multiphysics software. The simulation results of electric field distribution and temperature distribution in cavity present similar trend to the experimental results. Experimentally, the degradation of ethanol, benzene and acetone were carried out in this reactor for 50 W and 70 W at 2.45 GHz with the concentration and gas flow rate of 1000 ppm and 18 L/min. At 70 W and 2.45 GHz, the degradation efficiency of ethanol, benzene and acetone reached 99%, 70% and 99%, leading higher energy efficiency than other VOCs degradation methods.

Simulation and prediction study of hydrogenation/dehydrogenation kinetics based on the universal changing-volume model

Considering the expansion/shrinkage of metal hydride particles during hydriding/dehydriding, the hydrogenation/dehydrogenation kinetics cannot be described and predicted as expected. A universal changing-volume model (UCVM) was proposed to simplify the model expression and improve kinetics accuracy, meanwhile a model parameter (ξ) was introduced to address the effect of working conditions on kinetics. Both crystal parameter and density were simulated after crystal geometry optimization based on First-principles calculations, and H2 absorption/desorption experiments of LaNi4.5Co0.5 were employed to verify the availability of UCVM. The experimental results indicated that UCVM owned the highest model precision among several typical models. Moreover, UCVM performed a broad adaptability for other metal hydrides, and its calculation results demonstrated a prominent agreement with the experimental data of FeTi and Mg1.95Ag0.05Ni. In general, the prediction system of UCVM can precisely forecast the kinetics process under various operation conditions, which can be further developed to some liquid-solid and gas-solid catalytic reactions.

High-performance CrN tight ultrafiltration membranes prepared by in situ gas–solid catalytic reaction

To expand the industrial application of membranes, high-performance CrN tight ultrafiltration membranes (UF) were prepared by in situ gas–solid reaction using Cr2O3 as a nanoprecursor and TiO2 as a nitriding catalyst in ammonia atmosphere. The phase composition and microstructure of CrN UF membranes were characterized by X-ray diffraction and field-emission scanning electron microscopy with energy-dispersive X-ray spectroscopy. The effects of TiO2 and sintering parameters on the crystalline phase and pore size of CrN UF membranes were investigated. The results identified Ti4+ as a key factor influencing the transformation of the Cr2O3 phase into the CrN phase. The as-prepared CrN membranes exhibited enhanced hydrophilicity, no cracks or pinholes, water flux of 121 L·m−2h−1 bar−1, and a molecular weight cut-off of 1500 Da. The membranes also had retention rates of 100% for methyl blue (50 ppm) and 90% for methylene blue (50 ppm), which almost remained constant under repeated use.

Revisiting the Role of Mass and Heat Transfer in Gas–Solid Catalytic Reactions

The tremendous progress in the computing power of modern computers has in the last 20 years favored the use of numerical methods for solving complex problems in the field of chemical kinetics and of reactor simulations considering also the effect of mass and heat transfer. Many classical textbooks dealing with the topic have, therefore, become quite obsolete. The present work is a review of the role that heat and mass transfer have in the kinetic studies of gas–solid catalytic reactions. The scope was to collect in a relatively short document the necessary knowledge for a correct simulation of gas–solid catalytic reactors. The first part of the review deals with the most reliable approach to the description of the heat and mass transfer outside and inside a single catalytic particle. Some different examples of calculations allow for an easier understanding of the described methods. The second part of the review is related to the heat and mass transfer in packed bed reactors, considering the macroscopic gradients that derive from the solution of mass and energy balances on the whole reactor. Moreover, in this second part, some examples of calculations, applied to chemical reactions of industrial interest, are reported for a better understanding of the systems studied.

Keggin heteropolyacid supported on BN and C3N4: Comparison between catalytic and photocatalytic alcohol dehydration

The Keggin heteropolyacid (HPA), H3PW12O40 (PW12) has been supported on commercial boron nitride (BN) and two types of home prepared carbon nitride (C3N4). The supported PW12 was used in the gas-solid (photo)catalytic 2-propanol dehydration reaction to give propene at atmospheric pressure and temperatures in the range 70–120 °C and resulted more active than the pristine PW12. Reaction rate increased by increasing the temperature. Noticeably, the propene formation rate was higher by irradiating the catalytic system. The PW12/BN material resulted more active than PW12/C3N4. The acidity of the HPA cluster accounts for the catalytic role, whereas both the acidity and the redox properties of the HPA species were responsible for the increase of the reaction rate in the photo-assisted catalytic reaction.

Application of Mathematical Modeling in Optimization of Synthesis Process Parameters of Methylchlorosilane

Methylchlorosilane is an important chemical raw material. It has been matured since the direct synthesis technology has been applied for many years. However, due to the characteristics of gas-solid two-phase catalytic reaction, it still faces many problems in industrial production. The use of systems engineering methods to solve production problems has become an important task for organic chlorosilane monomer manufacturers. This paper introduces the application of mathematical modeling in the optimization of methylchlorosilane synthesis process parameters as an example to illustrate the important role of system engineering ideas in the production practice process, to achieve digitization of the fluidized bed reactor control process, parameter optimization. Through the research and analysis of the production control process, the mathematical model of superficial gas velocity and catalyst feed coefficient control was established to optimize the methylchlorosilane synthesis process. The results show that the apparent gas velocity should be controlled in stages during the direct synthesis of methylchlorosilane. The induction period is 0.10~0.12 m/s, and the stable period is 0.25~0.28 m/s. After the catalyst is added to the reactor, it will undergo three stages of induction period, stable period and aging period. After the catalyst reaction performance, the catalyst will gradually lose its catalytic ability due to various physical and chemical factors. Catalyst stability and life-span in industrial production are related to its own performance and mixing ratio, the ternary copper catalyst life-span is generally 50-60 hours, the suitable mixing ratio is 2.0-2.5%.

Infrared Thermopile Temperature Measurement Technique in Microwave Heating Systems

Temperature measurement in microwave systems is essential for thermally driven processes, namely, catalytic reactions and ceramic sintering. Although, the application of direct thermometry methods, namely, thermocouples, have been commonly articulated in the available literature, however, contacted temperature measurement mechanisms have aroused concerns associated with the disruption of the electromagnetic field and local distortion of the field pattern leading to unprecedented measurement uncertainties. Consequently, the application of optical measurement methods has been advocated to diminish the associated concerns. However, due to the economical constrains and measurement range restrictions, the application of optical measurement systems, namely, pyrometers and optical fibers, has been deferred. In this study, an infrared thermopile, a precise and feasible temperature measurement system has been developed and calibrated to perform in microwave irradiation. Furthermore, the accuracy of the developed temperature system has been compared with the thermometry technique. It was concluded that thermopile stipulates unrivalled precision, succeeding a profound calibration procedure. It was further demonstrated that the thermopile is capable of the temperature measurement of the dielectric surfaces, exclusively, while the grounded thermocouple monitored the bulk temperature, a proportion of the gas phase and the solid phase temperature values. Consequently, the application of a thermopile coupled with a thermometry measurement method has been proposed to monitor the temperature of the dielectric catalyst active sites in gas-solid catalytic microwave-heated reactions.

Adsorption properties of NO, NH3, and O2 over β-MnO2(110) surface

Selective catalytic reduction (SCR) of NOx with NH3 has been widely adopted to reduce NOx emissions. Although MnOx-based catalysts exhibit higher NOx conversion, the underlying reaction mechanism is still unclear. Since the SCR is a gas–solid catalytic reaction, the adsorption of related gas species on the catalyst surface plays a key role. In this study, the adsorption of NO, NH3, and O2 on β-MnO2(110) surface was investigated by density functional theory calculations, showing their individual adsorption properties. Two different gas molecules can also simultaneously adsorb on the same adsorption site. When NO and O2 co-adsorb on the surface, NO is oxidized by O2 to form bridge nitrates and nitrites. This work provides a foundation for studying the mechanism of the SCR of NOx with NH3.

Gas Flow Characteristics in a Rotating Packed Bed by Particle Image Velocimetry Measurement

The rotating packed bed (RPB) has drawn wide attention owing to its outstanding advantage in process intensification. In the present study, gas flow characteristics in RPB were investigated by particle image velocimetry (PIV) measurement. The velocity and turbulent kinetic energy (TKE) in the packing zone were obtained and the effects of various parameters were analyzed. During rotation, gas rapidly acquired tangential velocity, which was dominant in resultant velocity. Mean gas velocity increased with the increase of rotational speed, but was almost independent of gas flow rate and packing size at lower rotational speed. Moreover, mean radial and tangential slip velocities were overall positively affected by gas flow rate and rotational speed, respectively. Higher TKE near the inner packing than those in the bulk zone revealed the existence of a gas end-effect zone in RPB. The results could provide a theoretical basis for further study on gas–solid catalytic reaction or the gas–liquid mass transfer proce...

Synergistic Effect of Mo–Fe Bimetal Oxides Promoting Catalytic Conversion of Glycerol to Allyl Alcohol

In this study, KIT-6 silica with well-ordered 3-D mesoporosity was developed as support to prepare Fe/KIT-6, Mo/KIT-6, and MoFe-x/KIT-6 (x = 0.25, 0.3, and 0.35) oxide catalysts for catalytic conversion of gas-glycerol into allyl alcohol. The catalysts were also characterized by XRD, BET, XPS, H2-TPR, and NH3-TPD. The catalytic conversion of glycerol showed a positive correlation with the surface moderate acid density of catalysts, following the order of Fe/KIT-6 < MoFe0.25/KIT-6 < MoFe0.35/KIT-6 < MoFe0.3/KIT-6 < Mo/KIT-6. Differently, the production of allyl alcohol was closely related with the moderate redox sites following a hydrogen transfer mechanism. The MoFe-x/KIT-6 showed much higher selectivity than the Fe/KIT-6 and Mo/KIT-6, which resulted from the strong synergistic effect between Fe2O3 and MoO3 altering the surface moderate acid strength, surface acid amounts, and reducibility of catalysts. The MoFe-0.3/KIT-6 exhibited a remarkable yield of 26.8% of allyl alcohol at 94.0% conversion of glycerol without external hydrogen donors supplied to the system, which benefits from the good balance between moderate acidity and weak reducibility of catalysts. The developed cubic Ia3d meso-structure was also benefit for improving the catalytic stability of MoFe0.3/KIT-6. Allyl alcohol can produce from gas–solid catalytic conversion of glycerol over the weekly acidic Fe2O3 and MoO3 supported on SiO2. The yield of allyl alcohol can be significantly improved over the MoO3–Fe2O3/SiO2 composite oxide catalysts, because of the strong interaction between MoO3 and Fe2O3. The catalytic conversion of glycerol was positively related with the surface weak acid site density of catalysts, while the allyl alcohol seems to form over the redox sites. Comparing with the single component Fe2O3/SiO2and MoO3/SiO2 catalysts, the strong synergistic effect of MoO3 with Fe2O3 guarantee the MoO3–Fe2O3/SiO2 having relatively high surface week acid site density and certain reducibility, which showed a good balance between weak acidity and reducibility thus obviously increasing the allyl alcohol yield from 26.8 to 94% catalytic conversion of glycerol through gas–solid catalytic reaction without any additives.

Gas Phase UTE MRI of Propane and Propene.

Proton magnetic resonance imaging (1H MRI) of gases can potentially enable functional lung imaging to probe gas ventilation and other functions. Here, 1H MR images of hyperpolarized (HP) and thermally polarized propane gas were obtained using ultrashort echo time (UTE) pulse sequence. A 2-dimensional (2D) image of thermally polarized propane gas with ∼0.9 × 0.9 mm2 spatial resolution was obtained in <2 seconds, showing that even non-HP hydrocarbon gases can be successfully used for conventional proton magnetic resonance imaging. The experiments were also performed with HP propane gas, and high-resolution multislice FLASH 2D images in ∼510 seconds and non-slice-selective 2D UTE MRI images were acquired in ∼2 seconds. The UTE approach adopted in this study can be potentially used for medical lung imaging. Furthermore, the possibility of combining UTE with selective suppression of 1H signals from 1 of the 2 gases in a mixture is shown in this MRI study. The latter can be useful for visualizing industrially important processes where several gases may be present, eg, gas–solid catalytic reactions.

ChemInform Abstract: A Helicopter View of Microwave Application to Chemical Processes: Reactions, Separations, and Equipment Concepts

AbstractReview: 215 refs.

The graphene-meso-macroporous SiO2 supported Pt–Ni alloy nanocatalyst for preferential oxidation of CO in H2-rich gases

In this work, nanoparticles of Pt–Ni alloy were supported on a new kind of composite which composed of graphene sheets and meso-macroporous SiO2, and the composite supported Pt–Ni catalyst was applied to the preferential oxidation of CO (CO-PROX) in H2-rich gases. The bimetallic Pt–Ni alloy catalyst was characterized by using techniques of SEM, TEM, XRD, TPR, CO chemisorptions and XPS. The catalyst showed excellent catalytic performance for CO-PROX with high activity at low temperature, high selectivity and very good stability, which was attributed to the following characters of the catalyst: Pt–Ni nanoparticles were in alloy state and highly dispersed, Pt–Ni nanoparticles were preferentially loaded on the surface of graphene sheets, and the meso-macroporosity of the composite markedly improved the mass transferring ability. This is a case study, and this kind of catalysts can be extended to other gas–solid catalytic reactions.

A helicopter view of microwave application to chemical processes: reactions, separations, and equipment concepts

We present a helicopter view of microwave technology application to various reaction and separa- tion processes, including liquid-phase organic syntheses, gas-solid catalytic reactions, polymerizations, extrac- tion, distillation, crystallization, membrane separation, and adsorbent regeneration/dehydration. The overarch- ing aim is to demonstrate the breadth of potential appli- cations of microwave technology to chemical industry, with particular attention to separations, as this is a less explored microwave application area. In this context, some key findi ngs, opinions, and developments in the rel- evant literature are summarized. In addition, the present microwave equipment concepts for chemical processes are critically reviewed and new ones are put forward, as we believe that an important milestone in the road from laboratory-scale microwave experimentation to indus- trial-scale microwave-assisted chemical processing is the design and development of innovative microwave equip- ment concepts tailored for specific chemical processes.

LiNbO3—A Polar Material for Solid-Gas Artificial Photosynthesis

The photocatalytic fixation of CO2 to hydrocarbons was performed using LiNbO3. 0.126 cm2 of powdered LiNbO3 was irradiated with 64.2 mW/cm2 light from a mercury lamp with 10ml of water under 30% CO2/air. The LiNbO3 was held on a platen above the water to give a gas-solid catalytic reaction. Formic acid and formaldehyde were detected in the water after irradiation for 6 hours and produced at rates of 7.7 mmol and 1.1 μmol /hour. The calculated efficiency of the catalyst was calculated to be ca 2% which compared to 0.17% for TiO2 under the same conditions. MgO doped LiNbO3 was also tested and found to have an energy conversion efficiency of 0.72%.