Catalyst Utilization Efficiency Research Articles

Segmented catalyst layer with varied catalyst loading to improve the cost performance of proton exchange membrane electrolysis cell, a numerical investigation

In this work, a steady-state, three-dimensional and non-isothermal numerical model for a proton exchange membrane electrolysis cell (PEMEC) is established. Based on this model, the distribution of catalyst loading is specifically designed according to the flow characteristics of both parallel and serpentine channels. In general, the catalyst loading is progressively reduced from inlet to outlet along the flow direction to match the local water content, leading to an innovative segmented catalyst layer which has not been studied yet for PEMEC applications. The electrochemical behavior of different segmentation schemes is investigated by comparing their polarization curves normalized by either electrode area or catalyst loading, while other physical fields such as velocity, pressure, water mole fraction and temperature distributions are also characterized. The numerical results reveal that a reasonable distribution of catalyst can reduce its amount of usage while still maintaining most of the PEMEC performance. In other words, the cost performance is significantly improved. This is mainly attributed to the full use of uneven water distribution in the flow channel, which improves the catalyst utilization efficiency significantly. This strategy is proved to be effective for both serpentine and parallel channels, ensuring a broad application prospect.

Self-terminated electrodeposition of Pt group metal: principles, synthetic strategies, and applications

Hydrogen, characterized by its carbon-neutral attributes and high energy density, is gaining momentum as a promising energy source. Platinum group metal (PGM) catalysts have emerged as pivotal components in water electrolysis and fuel cell technologies. However, their constrained availability and high cost impede the advancement of energy conversion systems. To address these challenges, various strategies have been explored within the realm of PGM catalysts. Particularly noteworthy are catalysts that exhibit an overlayer structure, offering exceptional catalyst utilization efficiency, bimetallic synergies, and strain-induced enhancements. Self-terminated electrodeposition (SED) stands out as a technique that enables precise atomic layer electrodeposition within an aqueous electrolyte environment. It allows meticulous control of metal loading quantities and surface coverage while operating at low temperatures and without the need for vacuum conditions. Catalysts with tailored properties achieved through SED exhibit distinct electrochemical reactivity compared to bulk catalysts, showcasing exceptional electrocatalytic activity, particularly in terms of mass and specific activity. This comprehensive review provides insights into the SED phenomenon, elucidates methodologies for fabricating PGM electrocatalysts using SED, and highlights their applications in water electrolysis and fuel cells.

Ionomer-free nanoporous iridium nanosheet electrodes with boosted performance and catalyst utilization for high-efficiency water electrolyzers

Increasing the catalyst utilization efficiency and simplifying electrode fabrication processes are crucial to accelerate development of low-cost proton exchange membrane electrolyzer cells (PEMECs). Here, we develop a facile route to fabricate ionomer-free iridium nanosheet integrated electrodes, in which nanoporous iridium nanosheets (IrNS) with abundant exposed edges and nanopores are deposited on thin titanium liquid/gas diffusion layers (TT-LGDLs) via a low-temperature chemical synthesis strategy. Benefiting from high catalytic activity, good electrode conductivity and excellent liquid/gas transport properties, such nanoporous IrNS electrodes with low catalyst loadings require low cell voltages of 1.65 V and 1.78 V at 3000 and 6000 mA/cm2, respectively. More impressively, a stable performance can be well maintained under extremely high current density tests of 5000 mA/cm2, demonstrating the potential of low-loading nanoporous IrNS electrodes in solid-electrolyte based electrochemical conversion cells that require high current density operation.

Study on solar-driven methanol steam reforming process in parabolic trough solar receiver-reactors by developing an optical-thermal-chemical model of realistic porosity distributions

The catalyst particle packing characteristics have a significant impact on improving the comprehensive energy conversion performance and economic benefits of sustainable solar-driven thermochemical hydrogen production systems. However, corresponding accurate and efficient numerical research tools or methods still need to be developed. In this paper, a three-dimensional comprehensive optical-thermal-chemical coupling model with catalyst particle packing characteristics is proposed for the parabolic trough solar receiver-reactor (PTSRR) of methanol steam reforming reaction (MSRR) for hydrogen production. This model is developed by combining a Monte Carlo ray tracing optical model, a computational fluid dynamics model, a MSRR comprehensive kinetic model with a Blender rigid body packing model. After validation, it was found from comparisons with previous studies that this model can represent relatively realistic catalyst porosity distributions of packed-bed reactors at a very low computational cost. Then, this model was applied to obtain the porosity of different PTSRR-MSRRs and optimize the catalyst size and shape, to achieve better comprehensive performance as well as economic benefits of higher overall efficiency and catalyst utilization efficiency. The results reveal that the PTSRR-MSRRs filled with cylinders and Raschig rings (R-PTSRR) can achieve similar high methanol conversion rate, while the R-PTSRR has more advantages with its lower average resistance coefficient and CO selectivity. After weighing the methanol conversion rate, the overall efficiency and the catalyst utilization efficiency, the optimum R-PTSRR is highly recommended. This study provides a useful option for rapid comprehensive analysis and optimization of similar solar-driven thermochemical conversion processes on catalyst particle packed beds.

Anaerobic environment-induced efficient degradation of chloroquine phosphate: Insights into the role of metal-free C3N4 nanotube in visible light-driven peroxymonosulfate activation

Catalytic efficiency is the main bottleneck in metal-free photocatalyst-mediated visible light-driven peroxymonosulfate (PMS) activation processes (PMS-Vis). In this study, a nanotubular carbon nitride (C3N4 NT) photocatalyst was prepared and applied to a PMS-Vis system to degrade chloroquine phosphate (CQP). The special structure and excellent photoelectrochemical properties of C3N4 NT optimized its active site exposure and charge transport performance, which in turn enabled its use as a photocatalyst for PMS activation and CQP degradation. Importantly, the anaerobic environment enhanced the degradation performance, and the degradation kinetic constant for the C3N4 NT/PMS-Vis-N2 system reached 0.0898 min−1 at a 0.2 g·L−1 catalyst dosage and 0.8 mM PMS concentration. Mechanistic studies and theoretical calculations clarified that the anaerobic environment prevented the competitive adsorption and consumption behavior of dissolved O2 and PMS on the photocatalyst surface, thus maximizing the transfer of surface photogenerated charges to PMS for PMS activation and active species generation. Thus, CQP was efficiently degraded, and its toxicity was reduced. The developed process demonstrated high catalyst utilization efficiency and overcame interference from real water matrices. This study provides a reference for improving the environmental applicability of metal-free photocatalysts and developing water treatment technologies for anaerobic environments.

Foam structured membrane reactor for distributed hydrogen production

Membrane reactor is one of the most potential methods for methane steam reforming process to achieve distributed hydrogen production. Mass, heat transfer and catalyst cost are the main hurdles to achieve its scaleup and practical applications. Here, we adopt structured foam SiC to construct Foam Structured Membrane Reactor (FSMR) and conduct systematic experimental study including catalytic reaction, membrane separation and integrated membrane reactor. The results indicate that FSMR can significantly intensify radial heat transfer (e.g., increase membrane side temperature about 20 °C) and radial mass transfer (e.g., faster H2 transfer to membrane) compared to conventional particles-packed membrane reactor (PMR). The mechanism is related to 3D continuous skeleton, cellular structure, and high thermal conductivity of structured solid foam. Also, FSMR can save more than 78% catalyst amount and achieve nearly 100% catalyst utilization efficiency.

CFD modelling and simulation of a zeolite catalytic membrane reactor for low temperature water-gas shift reaction

In this work, a catalytic membrane reactor is proposed to couple water-gas shift reaction with selective separation of H2 product to improve the overall conversion. A 3D isothermal CFD model of this catalytic membrane reactor is developed with COMSOL Multiphysics software. The effects of reaction temperature, pressure, sweep gas flow rate and reactor geometry on CO conversion and H2 recovery are analysized in details. Based on the results, the coupling mechanism of reaction, and H2 permeation is proposed. It is found that that the catalyst bed could be divided into active and less-active volume and reducing less-active volume helps improve the utilization efficiency of catalyst. As a conclusion, H2 permeation directly affects H2 mole fraction in near-membrane area, and the effect is spreaded to the rest part to boost the local reaction rate. However, the effect is neutralized by the improved H2 production and permeation affecting volume is mainly less-active volume while active volume is hardly to be affected. Our study indicates that H2 permeation tends to deplete H2 fraction in catalyst volume but the consequent improved reaction rate acts as a resistance and tends to move back to a new steady state.

Enhanced activation of PMS by a novel Fenton-like composite Fe3O4/S-WO3 for rapid chloroxylenol degradation

Chloroxylenol (PCMX) is widely used as disinfectant since the epidemic outbreak due to its effective killing of Covid-19 virus. Its stable chemical properties make it frequently detected in surface water. Herein, we successfully modified Fe3O4 nanoparticles with S-WO3 (X-Fe3O4/S-WO3) to accelerate the Fe2+/Fe3+ cycle. The composite has outstanding PCMX degradation and peroxymonosulfate (PMS) decomposition efficiency over a wide pH range (3.0 ∼ 9.0). 80-Fe3O4/S-WO3/PMS system not only increased PMS decomposition efficiency from 27.7% to 100.0%, but also realized an enhancement of PCMX degradation efficiency by 16 times in comparison with that of Fe3O4 alone. The catalyst utilization efficiency reached 0.3506 mmol∙g−1∙min−1 which stands out among most Fenton-like catalysts. The composite has excellent degradation ability to a variety of emerging pollutants, such as antibiotics, drugs, phenols and endocrine disrupters, and at least a 90% removal efficiency reached in 10 min. The degradation of PCMX was dominated by HO•, SO4•− and 1O2. The degradation pathways of PCMX were analyzed in detail. The component WS2 in S-WO3 plays a co-catalytic role instead of WO3. And the exposed active W4+surf. efficiently enhanced the Fe3+/Fe2+ cycle, thereby complete PMS decomposition and high catalytic efficiency were achieved. Our findings clarify that applying two-dimensional transition metal sulfide WS2 to modify heterogeneous Fe3O4 is a feasible strategy to improve Fenton-like reaction and provide a promising catalyst for PCMX degradation.

Proton selective anode nanochannel for efficient methanol utilization

A large area of freestanding graphdiyne films with an independent anode array of GDY@PtCu was prepared. Structural analysis confirmed that electroactive Pt4.4Cu alloy nanoparticles with a diameter size of 4.2 nm, which can be anchored on the inner wall of the GDY nanochannel. This highly active anodic electrode demonstrates intrinsic selectivity and efficient suppression of methanol crossover and achieves selective proton transport in the electrode, due to GDY special surface and super-large pore structure. Our results show that, in this process, the methanol diffusion pathway is highly ordered, methanol electrooxidation is effectively confined in ordered GDY nanochannels. As-prepared GDY@PtCu anode not only demonstrated superior electrocatalytic activity and duration, at the same time, the utilization efficiency of catalyst and methanol fuel is greatly improved. A DMFC using such an anodic electrode material exhibits superior power density of 90 mW cm-2 at 80 °C with an ultralow Pt loading (0.8 mg cm-2) and the methanol crossover is greatly suppressed up to 33%. After a 500 h long-term testing, the DMFC based-on freestanding GDY@PtCu anode still maintains high retention (81%) of its original power density.

Steam activation of Fe-N-C catalyst for advanced power performance of alkaline hydrazine fuel cells

Alkaline hydrazine liquid fuel cells (AHFC) have been highlighted in terms of high power performance with non-precious metal catalysts. Although Fe-N-C is a promising non-Pt electrocatalyst for oxygen reduction reaction (ORR), the surface density of the active site is very low and the catalyst layer should be thick to acquire the necessary number of catalytic active sites. With this thick catalyst layer, it is important to have an optimum pore structure for effective reactant conveyance to active sites and an interface structure for faster charge transfer. Herein, we prepare a Fe-N-C catalyst with magnetite particles and hierarchical pore structure by steam activation. The steam activation process significantly improves the power performance of the AHFC as indicated by the lower IR and activation voltage losses. Based on a systematic characterization, we found that hierarchical pore structures improve the catalyst utilization efficiency of the AHFCs, and magnetite nanoparticles act as surface modifiers to reduce the interfacial resistance between the electrode and the ion-exchange membrane.

(Invited) From Atomic-Scale Understanding to Design of Advanced Electrocatalyst Materials

Increasing concerns regarding the environmental impact of power generation and the reduction of carbon emissions have become a major motivation for the use of sustainable electrical power. In this perspective, renewable energy sources are expected to take up an important part of electric energy produced in the near future. Since renewable sources such as wind and solar are intermittent in nature, their increased installation will result in either excessive or insufficient power generation at times. A large variety of concepts for using this surplus power is currently under development.Acidic water electrolysis is an attractive environmentally-safe solution for the conversion and storage of excess electricity into hydrogen and oxygen. The large scale application of water electrolysis systems is currently hindered by low efficiency and instability of catalysts during long term operation [1]. This is especially crucial for the anodic oxygen evolution reaction (OER) which catalyzed by Iridium based alloys and oxides making the issues related to efficiency of catalyst utilization and durability even more critical. The development of catalyst materials with superior performance demands a deep understanding of the OER itself as well as electrocatalysts degradation mechanisms. Although a large number of possible OER mechanisms have been proposed [2], the topic remains a subject of intensive debates across the scientific literature, since the intermediates and their possible interrelations are in most cases unknown. Additional challenges in mechanistic studies are related to the changes in the composition of the catalyst and its degradation triggered by OER. Though the existence of experimental correlation between the structure, activity of OER catalyst and its dissolution was numerously reported and discussed [2,3], reports addressing all these aspects in one study are rare. This indicates that further research efforts are required to reveal reaction intermediates and products by means, for instance, of mass spectrometry at the atomic scale by atom probe tomography, that complement spectroscopic insight from synchrotron-based experiments, ideally in operando conditions.In this presentation, the main fundamental limitations that hinder the current understanding of the reactions mechanisms occurring in water electrolysis will be discussed. It will be stressed that only the combination of insights enables the establishing of reliable structure-function relationships in electrocatalyst materials. We present our approach to investigate complex processes in electrocatalysis with a combination of independent methods like online electrochemical mass spectrometry, atom probe tomography and synchrotron-based spectroscopy [4,5]. In particular, we discuss approaches to resolving the reaction mechanism on constantly evolving surfaces; present our recent results on the interplay between the nature of the active sites in Ir-based oxides and their stability towards the OER and establish structure–function relationships between the reactivity and the atomic-scale surface structure [5]. Finally, using the new insights gained in our recent studies [4-6], we discuss potential design strategy for Ir-based OER catalysts with high catalytic activity and long-term stable performance.[1] S. Cherevko et al., Catalysis Today 2016, 262, 170-180[2] T. Reier, H.N. Nong, D. Teschner, R. Schlögl, P. Strasser, Adv. Energy Mater. 2017, 7(1), 1601275.[3] O. Kasian, J.P. Grote, S. Geiger, S. Cherevko, K.J.J. Mayrhofer, Angew. Chem. Int. Ed. 2018, 57, 2488 –2491.[4] K. Schweinar, R.L. Nicholls, C.R. Rajamathi, P. Zeller, M. Amati, L. Gregoratti, D. Raabe, M. Greiner, B. Gault, O. Kasian, J. Mater. Chem. A 2020, 8(1), 388-400.[5] O. Kasian, S. Geiger, T. Li, J-P. Grote, K. Schweinar, S. Zhang, C. Scheu, D. Raabe, S. Cherevko, B. Gault, K. Mayrhofer, Energy Environ. Sci. 2019, 12(12), 3548-3555.[6] K. Schweinar, I. Mouton, B. Gault, O. Kasian, J. Phys. Chem. Lett. 2020, submitted.

Solid Acid Electrochemical Cell for the Production of Hydrogen from Ammonia

Summary Production of high-purity hydrogen by thermal-electrochemical decomposition of ammonia at an intermediate temperature of 250°C is demonstrated. The process is enabled by use of a solid-acid-based electrochemical cell (SAEC) in combination with a bilayered anode, comprising a thermal-cracking catalyst layer and a hydrogen electrooxidation catalyst layer. Cs-promoted Ru on carbon nanotubes (Ru/CNT) serves as the thermal decomposition catalyst, and Pt on carbon black mixed with CsH2PO4 is used to catalyze hydrogen electrooxidation. Cells were operated at 250°C with humidified dilute ammonia supplied to the anode and humidified hydrogen supplied to the counter electrode. A current density of 435 mA/cm2 was achieved at a potential of 0.4 V and ammonia flow rate of 30 sccm. With a demonstrated faradic efficiency for hydrogen production of 100%, the process yields hydrogen at a rate of 1.48 m o l H 2 / g c a t h .

Electrodeposition of High-Surface-Area IrO2 Films on Ti Felt as an Efficient Catalyst for the Oxygen Evolution Reaction

Under acidic conditions, IrO2 exhibits high catalytic activity with respect to the oxygen evolution reaction (OER). However, the practical application of Ir-based catalysts is significantly limited owing to their high cost in addition to the scarcity of the metal. Therefore, it is necessary to improve the efficiency of the utilization of such catalysts. In this study, IrO2-coated Ti felt (IrO2/Ti) electrodes were prepared as high-efficiency catalysts for the OER under acidic conditions. By controlling the surface roughness of the Ti substrate via wet etching, the optimum Ti substrate surface area for application in the IrO2/Ti electrode was determined. Additionally, the IrO2 film that was electrodeposited on the 30 min etched Ti felt had a large surface area and a uniform morphology. Furthermore, there were no micro-cracks and the electrode obtained (IrO2/Ti-30) exhibited superior catalytic performance with respect to the OER, with a mass activity of 362.3 A at a potential of 2.0 V (vs. RHE) despite the low Ir loading (0.2 mg cm−2). Therefore, this proposed strategy for the development of IrO2/Ti electrodes with substrate surface control via wet etching has potential for application in the improvement of the efficiency of catalyst utilization with respect to the OER.

Comparison of catalyst-coated membranes and catalyst-coated substrate for PEMFC membrane electrode assembly: A review

Catalyst-coated membranes (CCMs) have gained popularity among membrane electrode assembly (MEA) fabricators for their abilities and advantages compared with those of other methods, such as catalyst-coated substrates (CCSs). CCMs show a profound new analysis for reducing platinum (Pt) catalyst loading. In addition, they increase the total number of reactions that occur on the MEA because of their active area amplification, which leads to an improved catalyst-utilization efficiency rate. Moreover, several characteristics are involved in the MEA fabrication methods. Material-manufacturing effects with regard to catalyst inks and analysis of the overall performance of MEAs prepared by the CCM and CCS methods are deliberated. This deliberation emphasizes the practical approaches in minimizing performance deterioration during the fabrication of MEAs using the CCM method and converses the commercialization of the CCM fabrication method toward developing an end product. Novel research is required for MEA fabrication using the CCM methods to ensure that the fuel cell performance is improved. Therefore, this review is focusing on the pros and cons of both distinguished methods, that is, CCM and CCS fabrication, for better comparison.

Hydrogen production via steam reforming of coke oven gas enhanced by steel slag-derived CaO

Steel slag, a waste from steelmaking plant, has been proven to be good candidate resources for low-cost calcium-based CO2 sorbent derivation. In this work, a cheap and sintering-resistance CaO-based sorbent (CaO (SS)) was prepared from low cost waste steel slag and was applied to enhance catalytic steam reforming of coke oven gas for production of high-purity hydrogen. This steel slag-derived CaO possessed a high and stable CO2 capture capacity of about 0.48 g CO2/g sorbent after 35 adsorption/desorption cycles, which was mainly ascribed to the mesoporous structure and the presence of MgO and Fe2O3. Product gas containing 95.8 vol% H2 and 1.4 vol% CO, with a CH4 conversion of 91.3% was achieved at 600 °C by steam reforming of COG enhanced by CaO (SS). Although high temperature was beneficial for methane conversion, CH4 conversion was remarkably increased at lower operation temperatures with the promotion effects from CaO (SS), and CO selectivity has been also greatly decreased. Reducing WHSV could increase methane conversion and reduce CO selectivity due to longer reactants residence time. Reducing C/A could increase methane conversion and hydrogen recovery factor, and also decrease CO selectivity. When being mixed with catalyst during SE-SRCOG, CaO (SS) with a uniform size distribution favored methane conversion due to the high utilization efficiency of catalyst. Promising stability of CaO (SS) in cyclic reforming/calcination tests was evidenced with a hydrogen recovery factor >2.1 and CH4 conversion of 82.5% at 600 °C after 10 cycles using CaO (SS) as sorbent.

Performance Study on Methanol Steam Reforming Rib Micro-Reactor with Waste Heat Recovery

Automobile exhaust heat recovery is considered to be an effective means to enhance fuel utilization. The catalytic production of hydrogen by methanol steam reforming is an attractive option for onboard mobile applications, due to its many advantages. However, the reformers of conventional packed bed type suffer from axial temperature gradients and cold spots resulting from severe limitations of mass and heat transfer. These disadvantages limit reformers to a low efficiency of catalyst utilization. A novel rib microreactor was designed for the hydrogen production from methanol steam reforming heated by automobile exhaust, and the effect of inlet exhaust and methanol steam on reactor performance was numerically analyzed in detail, with computational fluid dynamics. The results showed that the best operating parameters were the counter flow, water-to-alcohol (W/A) of 1.3, exhaust inlet velocity of 1.1 m/s, and exhaust inlet temperature of 773 K, when the inlet velocity and inlet temperature of the reactant were 0.1 m/s and 493 K, respectively. At this condition, a methanol conversion of 99.4% and thermal efficiency of 28% were achieved, together with a hydrogen content of 69.6%.

IrO2 coated TiO2 core-shell microparticles advance performance of low loading proton exchange membrane water electrolyzers

Herein we present novel IrO2 coated TiO2 core-shell microparticles (IrO2@TiO2) as an oxygen evolution reaction catalyst. We compare the IrO2@TiO2 catalyst to commercial TiO2 supported IrO2 catalyst (IrO2/TiO2) and pure IrO2 catalyst powder. A stability analysis via on-line inductively coupled plasma mass spectrometry based on the S-number, a descriptor considering both energy efficiency and catalyst utilization efficiency, shows that the IrO2@TiO2 catalyst shows high potential for practical applications. This was further confirmed by full-cell tests showing superior performance of the IrO2@TiO2 catalyst with moderate and low loadings of 1.2 mgIr cm−2 and 0.4 mgIr cm−2, respectively. The core-shell catalyst is synthesized via facile route suitable for large quantities. Moreover, stable inks from the synthesized catalyst powder make this system appealing for large scale manufacturing of cells. Given the facile synthesis route, high activity, and good stability, the IrO2@TiO2 catalyst is potentially suitable for industry proton exchange membrane water electrolysis application.

Poly[2,2'-(4,4'-bipyridine)-5,5'-bibenzimidazole] functionalization of carbon black for improving the oxidation stability and oxygen reduction reaction of fuel cells.

The rapid oxidation of carbon black (CB) is a major drawback for its use as a catalyst support in polymer electrolyte fuel cells. Here, we synthesize poly[2,2′-(4,4′-bipyridine)-5,5′-bibenzimidazole] (BiPyPBI) as a conducting polymer and use it to functionalize the surface of CB and homogenously anchor platinum metal nanoparticles (Pt-NPs) on a CB surface. The as-prepared materials were confirmed by different spectroscopic techniques, including nuclear magnetic resonance spectroscopy, energy-dispersive X-ray, thermal gravimetric analysis, and scanning-transmittance microscopy. The as-fabricated polymer-based CB catalyst showed an electrochemical surface area (ECSA) of 63.1 cm2 mgPt−1, giving a catalyst utilization efficiency of 74.3%. Notably, the BiPyPBI-based CB catalyst exhibited remarkable catalytic activity towards oxygen reduction reactions. The onset potential and the diffusion-limiting current density reached 0.66 V and 5.35 mA cm−2, respectively. Furthermore, oxidation stability testing showed a loss of only 16% of Pt-ECSA for BiPyPBI-based CB compared to a 36% loss of Pt-ECSA for commercial Pt/CB after 5000 potential cycles. These improvements were related to the synergetic effect between the nitrogen-rich BiPyPBI polymer, which promoted the catalytic activity through the structural nitrogen atoms, and demolished the degradation of CB via the wrapping process.

Thin-felt microfibrous-structured Au-α-Fe2O3/ns-γ-Al2O3/Al-fiber catalyst for high-throughput CO oxidation

Gold nanoparticles supported on Fe2O3 are a promising type of catalyst for CO oxidation. One challenge for their application in the real world is developing novel monolithic catalytic packings to meet the fundamental criteria (for example, high catalyst utilization efficiency and low pressure drop) needed for such high-throughput reaction process. Herein, a highly active and efficient thin-felt microfibrous-structured Au-α-Fe2O3/ns-γ-Al2O3/Al-fiber catalyst with unique form factor and high permeability is fabricated for the low-temperature CO oxidation. Initially, thin-felt Al-fiber felt (60 μm diameter; 85 vol% voidage) undergoes a steam-only oxidation and calcination to create a 0.7 μm mesoporous layer of γ-Al2O3 nanosheets (ns-γ-Al2O3) along with the Al-fiber. Subsequently, α-Fe2O3 is hydrothermally grown onto the ns-γ-Al2O3 layer followed by Au nanoparticle deposition via urea-assistant deposition-precipitation method. As-resulted microfibrous-structured Au-α-Fe2O3/ns-γ-Al2O3/Al-fiber catalysts effectively and efficiently couple the low-temperature activity and improved water vapor tolerance with enhanced catalyst accessibility and high permeability. The promising microfibrous-structured catalyst with only 0.14 wt% Au and 1.4 wt% α-Fe2O3 is capable of fully or 40% oxidizing CO into CO2 at 25 °C or 0 °C for a feed gas of 2 vol% CO and 0.3 vol% water vapor in air at a high linear velocity of 0.7 cm s−1, using a high gas hourly space velocity of 25,200 mL g−1 cat h−1. Moreover, the microfibrous-structured catalyst performs robustly for at least 232 h under the changeable temperature conditions. Interestingly, 3D hierarchical porous flake structure of α-Fe2O3 nano-sheets is detected other than the irregular micron-sized particles, leading to a 3-fold increase in the intrinsic activity (TOF of 0.46 s-1 for the Au-α-Fe2O3/ns-γ-Al2O3/Al-fiber vs. 0.11 s−1 for the Au-α-Fe2O3 powder at 25 °C).

Advances in the slurry reactor technology of the anthraquinone process for H2O2 production

This paper overviews the development of the anthraquinone auto-oxidation (AO) process for the production of hydrogen peroxide in China and abroad. The characteristics and differences between the fixed-bed and fluidized-bed reactors for the AO process are presented. The detailed comparison indicates that the production of hydrogen peroxide with the fluidized-bed reactor has many advantages, such as lower operation cost and catalyst consumption, less anthraquinone degradation, higher catalyst utilization efficiency, and higher hydrogenation efficiency. The key characters of the production technology of hydrogen peroxide based on the fluidized-bed reactor developed by the Research Institute of Petroleum Processing, Sinopec are also disclosed. It is apparent that substituting the fluidized-bed reactor for the fixed-bed reactor is a major direction of breakthrough for the production technology of hydrogen peroxide in China.