Inhibit Carbon Deposition Research Articles

Promoted deep oxidation of m-xylene and inhibited the generation of carbon-deposited species by Ce modified Co3O4: The key role of modulating internal electron transport pathway

The low-cost Co3O4 is one of the most promising catalysts for highly toxic VOCs removal, but its poor low temperature activity and deep oxidation capacity has seriously limited further practical application. Currently, optimizing the intrinsic electronic structure of Co3O4 and facilitating rapid cycling between Co2+ and Co3+ is considered to be a hopeful solution to this challenge. In this work, a series of Ce modified Co3O4 catalysts were successful synthesized and found that Ce not only improved the low temperature efficiency of Co3O4 for m-xylene oxidation, more importantly, significantly boosted its deep oxidation capacity. Ce0.06-Co3O4 achieved 100 % mineralization for m-xylene at 274 ºC while pure Co3O4 only reached 87.8 % even at 340 ºC. The XPS and DFT demonstrated that electrons were migrated along the direction of Co → O → Ce network thus promoted the generation of highly active Co3+ and oxygen vacancies in CeO2−Co3O4 heterojunctions. The continued stability testing and in situ DRIFTS revealed that Ce modification altered the m-xylene oxidation path and inhibited carbon deposition thus avoided the Co3O4 being inactivated under low temperature. This study can provide a new and in-depth perspective into the further targeted design and application of Co3O4 in the field of VOCs deep remediation.

Efficient Hydrodeoxygenation of Lignin-Derived Phenolic Compounds Over Ru-Based Catalyst with Biochar and Al2O3 as Composite Support.

Hydrodeoxygenation (HDO) is a common strategy for upgrading lignin-derived phenolic compounds into high-quality liquid fuels, and the support rational design of HDO catalysts is critical to achieve a good reaction performance. This work proposed a novel Ru-based catalyst with biochar and Al2O3 as composite support. The addition of biochar can enlarge the porous structure, and the addition of Al2O3 can enhance the acid property of the support. By regulating the content of biochar and Al2O3 components, Ru/CA-2 catalyst achieved the best HDO performance of lignin-derived phenolic compounds, with the optimal component balance of 50 %C and 50 %Al2O3. This catalyst possesses the high Ru metal dispersion (1.38 nm particle size) to activate the hydrogen source, the moderate acid property to suppress carbon deposition and the abundant oxygen vacancy to promote substrate adsorption at the same time. 99.9 % conversion of guaiacol is obtained at 230 °C, with 99.9 % selectivity towards cyclohexane. Ru/CA-2 catalyst also has a good recyclability, with no obvious activity loss after five runs. Furthermore, in the application of catalytic lignin-oil HDO, the content of hydrocarbons increase from 10.7 % to 95.7 %, showing great potential on the industrial usage.

Strategic conversion of plastic containers with food waste into energy through thermochemical processes

Plastic valorization has received particular attention as an environmentally benign approach to achieve carbon neutrality and reduce greenhouse gas emissions. However, contaminated plastic and biomass waste mixtures suffer from single-stream recycling. Waste mixtures are currently discarded through landfilling and incineration. As a sustainable disposal and valorization method for converting plastic and biomass waste mixtures into energy-intensive products, especially syngas (H2 and CO), this study utilizes catalytic pyrolysis and a CO2 flow gas. A plastic container contaminated with a food waste mixture (PFW) was used as the model waste. The major products of the pyrolysis of PFW were liquid hydrocarbons (HC) (C7–30) and wax-like HCs with negligible formation of oxygen-containing HCs. However, the high production of wax-like HCs becomes a problem. Catalytic pyrolysis was employed to convert HCs into simpler product streams such as syngas. Although syngas formation tripled with the Ni catalyst, catalyst deactivation was observed. To suppress catalyst deactivation and promote CO formation, CO2 was introduced instead of N2. During the CO2-assisted catalytic pyrolysis, the syngas yield from PFW increased to 95.5 % because the chemical reactions between CO2 and liquid/wax-like HCs produced additional H2 and CO. The catalytic reaction with CO2 suppressed carbon deposition because long-chain HCs were converted to CO rather than coke.

CeO2 enhanced performance of NiFe2O4-CaO for carbon capture and in-situ hydrogenation conversion to CO

NiFe2O4 exhibits excellent redox properties and is widely applied in CaO-NiFe2O4 chemical looping processes. However, rapid sintering of Ni-Fe alloy under reaction conditions limited its industrial applications. The CeO2-NiFe-CaO were synthesized through a physical mixing method with NiFe2O4 as a precursor, and its CO2 capture capacity and in-situ hydrogenation performance were conducted on ICCC-RWGS reaction under different conditions. 20CeO2-NiFe-CaO exhibited a CO yielding of 9.35 mmol/g at 650 °C. During the carbon capture stage, CO2 was adsorbed by CaO, leading to the formation of CaCO3. In the hydrogenation conversion stage, hydroxyl groups were generated on the surface, combining with CaCO3 to produce formate species, further generating H2O and CO. 15CNF-CaO exhibited superior cyclic ICCC-RWGS reaction performance compared to 15NF-CaO, with a CO yield of 1.88 mmol/g after 40 cycles. CeO2 inhibited the sintering of catalytic components, preserving a higher specific surface area and smaller particle size. Furthermore, CeO2 in 15CNF-CaO inhibited carbon deposition and enhanced in-situ hydrogenation performance, exhibiting better CaO regeneration capability and better cyclic stability. These results could provide insight for designing the DFMs for the ICCC-RWGS process.

Exploring the influence of different precursor materials on the catalytic performance and deactivation characteristics of iron-loaded biochar catalysts for the catalytic cracking of toluene

This study employed rice husks (RH), corn stalks (CS), and camphor leaves (CL) as biomass sources to prepare iron-loaded biochar catalysts, elucidating the key relationships between these biomass materials, their catalytic performance, and their resistance to deactivation in toluene. Experimental results indicated that the carbon deposits in the three spent catalysts are primarily composed of inert carbon (Cγ). The carbon peaks in these deposits primarily consisted of CO, CC, and CO structures, with varying proportions across the different types of spent catalysts. Specifically, the RH spent catalyst exhibited the highest relative content of the CO structure at 13.49 %, the CS spent catalyst showed the highest relative content of the CC structure at 89.19 %, and the CL spent catalyst displayed the highest relative content of the CO structure at 5.57 %. Fe2+ was the predominant species on the surfaces of all three spent catalysts, accounting for over 50 % in each case. Fe3C was detected on the surfaces of the CS and CL spent catalysts but was absent on the RH spent catalyst. After 80 min of reaction, the carbon deposition rate of the CL catalyst was 8.15 %, with a catalytic cracking efficiency of 28.04 %, making it the most effective overall. This effectiveness was attributed to the CL catalyst's highest oxygen vacancy intensity, where the abundant oxygen source effectively promoted the catalytic reaction of toluene and inhibited carbon deposition. After three consecutive regeneration cycles, the catalytic cracking efficiency of the CL catalyst remained above 70 %, demonstrating strong cyclic regeneration performance. This study provides theoretical insights into the effective utilization of agricultural and forestry waste, contributing to environmental protection.

Efficient catalysis and products regulation of methane dry reforming under mild temperature conditions using novel high-entropy catalyst

Dry reforming of methane to syngas (H2/CO) is the most dominant upstream reaction in chemical production line, which also helps capture greenhouse gases. In this work, we report a novel CoxNi0.8-xLa0.2Ca0.5Ce0.5@Al2O3 high-entropy catalyst applied to CH4-CO2 reforming reaction, which can widen the reaction-temperature window and achieve over 40 % methane conversion and 220 mmol·gcat−1·h−1 hydrogen yield at 500 °C. Compared with other studies, the activity of proposed CoxNi0.8-xLa0.2Ca0.5Ce0.5@Al2O3 high-entropy catalyst exhibits absolute advantage in low-medium temperature environments (500–650 °C). Due to the regulation of structure–activity relationship among various active metal elements, the proposed catalysts present synergistic effect within catalytic system, which can also suppress carbon deposition and maintain stable activity during a 12-hour continuous operation. Importantly, this research utilizes the remarkable characteristics of high-entropy alloys to induce the orderly transformation of reactants. The thermodynamic regulation of the reaction process is also improved by regulating the catalyst structure and thermal properties through intermetallic lattice distortion and “Maximum Entropy Theory”. The experimental results show that the product H2/CO ratio can be stably maintained over 0.9 for temperature ranging from 500 to 850 °C. This provides a reference for the application of high-entropy alloys in the field of carbon capture and hydrogen production.

SiO2-coated HZSM-5 catalysts for dehydration of bio-based glycerol to acrolein

As biodiesel production from triglyceride transesterification increases, by-product glycerol is accumulated, motivating the development of novel mechanism for converting glycerol into valuable chemicals. In the present work, for the selective production of acrolein from glycerol, SiO2-coated HZSM-5 molecular sieve with preciously controlled surface was designed. As characterized by NH3-TPD and pyridine adsorption IR, the total acid and the Lewis acid amounts of SiO2-coated HZSM-5 were decreased whereas the Brønsted acid amount remained almost unchanged. SiO2-coated HZSM-5 catalyst exhibited selectivity to acrolein of 64%, in glycerol conversion of 100% under reaction temperature of 300°C, much higher than HZSM-5 catalyst with acrolein selectivity of 52%. The catalytic activity durability was also improved by the modification of the surface properties because SiO2 coating reduced the surface acid amount and the micropore volume of HZSM-5, suppressing side reactions and inhibiting carbon deposition efficaciously.

Microwave heating-assisted chemical looping dry reforming of methane

Chemical looping dry reforming of methane (CLDRM) offers a sustainable pathway to convert methane (CH4) and carbon dioxide (CO2) to syngas, i.e., a mixture of hydrogen (H2) and carbon monoxide (CO). However, carbon deposition caused by high gas temperature remains a crucial challenge for the CLDRM. We proposed microwave (MW) heating-assisted CLDRM to leverage the selective heating feature of MWs to create a thermal gradient between solid and gas phases. This thermal gradient, i.e., a higher solid temperature than the gas temperature, can promote desired reduction and oxidation (redox) reactions, while suppressing undesired gas phase reactions, in particular, CH4 decomposition. At bulk temperature of 800 °C, the MW heating-assisted CLDRM achieved a maximum CH4 conversion of 97% and H2/CO ratio of around 2. Compared to the conventionally heated CLDRM, the MW heating increased the redox extents of magnetite (the oxygen carrier) by 2.5 and 1.5 times, respectively, and suppressed carbon deposition.

Mesoporous silica encapsulated core-shell NiRh@NiO nanocatalyst for performance-enhanced ethanol steam reforming

A novel mesoporous SiO2 encapsulated core-shell NiRh@NiO nanostructure was constructed to enhance the activity and stability of ethanol steam reforming (ESR). At 550 °C and ethanol-WHSV = 21 h−1, the specific activity and conversion loss (17 h) of NiRh@NiO@m-SiO2 were 0.42 molethanol/(gcat.·h) and 10.9 %. The alloying of NiRh core, dominated NiO in shell, and abundant mesopore of SiO2 were confirmed by systematic characterization techniques. The in situ DRIFTS results indicated that alloying Ni and Rh boosted ethoxide dehydrogenation to acetaldehyde and acetate demethanation to carbonate. ReaxFF molecular dynamics (MD) simulations suggested that NiO shell was conducive to water activation, which, in turn, promoted the conversion of CHxOy species. The SiO2 encapsulation derived confinement effect inhibited both metal core sintering and leaching caused by the filamentous carbon. The abundant mesopores of SiO2 ensured the facile in-diffusion of water and out-diffusion of carbonaceous products, suppressing carbon deposition within the SiO2 encapsulation and the destruction of core-shell structure.

Specific adsorptive properties and anodic polarization characteristics for hydrogen and methane in the Ni1-xCox solid-solution alloy combined with yttria-stabilized zirconia

The Ni-based cermet anode of a solid oxide fuel cell is prone to deactivation for the direct supply of CH4 due to carbon deposition. Discovered are specific adsorptive properties of Ni1-xCox solid-solution alloy catalysts combined with yttria-stabilized zirconia (Ni1-xCox-YSZ) using the temperature-programmed desorption technique. Decreasing the activation energy in the thermal desorption of adsorbed CH4 and CO from Ni1-xCox-YSZ accounts for minimizing the anodic polarization of the Ni/YSZ cermet by Co alloying in the electrochemical oxidation of CH4, suppressing carbon deposition.

Characteristics of bio-tar catalytic cracking by char’s inherent Fe2O3 and K2O for biomass gasification process

In this research, a newly-designed micro fluidized bed reaction analyzer (MFBRA) was used to evaluate the catalytic activity of char’s inherent Fe2O3 and K2O on bio-tar in Ar at temperatures of 1023 K, 1073 K, 1123 K, and 1173 K. The adopted samples of char and tar were obtained by biomass pyrolysis in Ar at 1273 K. Fe2O3- and K2O-loaded char were prepared by doping metal oxides on the demineralized char samples to simulate the inherent metal oxides in char. The real-time cracking properties of tar were examined and compared on the basis of the analyzer’s high heating rate, quick sample loading at the predetermined temperature, and online analysis of gas products. The results show that both Fe2O3 and K2O displayed obviously catalytic activity by improving tar conversion and reaction rate, and lowering activation energy (Ea). Compared to K2O at 1173 K, Fe2O3-loaded char promoted the generation of H2, CO, CO2, CH4, C3H6, and the total gas products with the conversion ratio (XFe2O3/K2O) of 2.04, 1.02, 1.24, 1.32, 1.56, and 1.12, respectively. However, it suppressed the formation of C2H6 with the XFe2O3/K2O of 0.43. Meanwhile, the maximum generation rates for CO, CO2, CH4, and the total gas products improved to different extent. During tar catalytic cracking, Fe2O3 suppressed carbon deposition on the char surface because of the larger specific area after experiments. Finally, the generation Ea of CH4, H2, CO, CO2, C3H6 and the total gas products by Fe2O3-loaded char further decreased drastically and that of C2H6 increased obviously. All of these indicated the catalytic activity of the inherent Fe2O3 in char was better than K2O.

Mn-doped NiTiO3 catalysts for hydrogen production via auto-thermal reforming of acetic acid

ABSTRACT Auto-thermal reforming (ATR) of acetic acid (HAc) offers a feasible, carbon-neutral way to produce hydrogen, and Ni-based catalysts were found effective in ATR, while catalytic deactivation by sintering and carbon deposition needs to be addressed. Therefore, novel Mn-doped NiTiO3 catalysts were prepared by evaporation induced self-assembly method and tested in ATR; characterizations were used to explore the internal catalytic relationship between the carrier and active metals. The experimental results indicated the NiTiO3 catalyst doped with 10 wt.% of MnO exhibited the highest activity and enhanced stability: the conversion of HAc was stable at 100% and the yield of hydrogen was recorded near 2.5 mol-H2/mol-HAc. The characterization results showed that the NiTiO3 catalyst presented the highest specific surface area at 7.5 m2/g. After reduction and activation, NiTiO3 was transformed into Ni0, while Mn replaced Ni in NiTiO3 and formed a stable phase of MnTiO3 perovskite, which presented confinement effect on Ni0, preventing migration of Ni0 at high temperature with a relatively stable particle size within 41.6-44.5nm. These MnTiO3-supported nickel species effectively promoted the conversion of intermediate products such as CH3CO*, inhibited carbon deposition and improved hydrogen selectivity, showing application potential for hydrogen production via ATR of HAc.

Ce doping boosted photothermal synergistic catalytic reforming of CH4 and CO2 into syngas over Ni/ZrO2 at medium-low temperature

Syngas production from dry reforming (DRM) of CO2 and CH4 is a promising technology to reduce carbon emission, however, harsh reaction condition required in conventional thermal catalytic DRM frequently leads to poor economy and severe carbon deposition in catalysts. Herein, the present work reports a novel photothermal synergistic catalytic (PTSC) DRM over Ce-doping Ni/ZrO2 catalyst at medium-low temperature. The maximum CO2/CH4 conversions (51.6% and 54.6%) were obtained for Ni–Ce/ZrO2 at 600 °C via synergy of illumination, which was about 1.3 times higher than that under thermal catalytic DRM. Ce doped catalyst maintained good activity and thermal stability after the aging test over 23 h. The TOF values of Ni–Ce bimetallic catalyst under PTSC condition have 1.2–3.3 times enhancement compared to thermal condition. Characterization and DFT calculation results reveal that Ce doping facilitates the formation of oxygen vacancies and effectively weakens C adsorption on Ni metal to suppress carbon deposition.

Light-driven thermocatalytic CO2 reduction by CH4 on alumina-cluster-modified Ni nanoparticles with excellent durability and high light-to-fuel efficiency promoted by the photoactivation effect

Using inexhaustible solar energy to drive efficient light-driven thermocatalytic CO2 reduction by CH4 (DRM) is an attractive approach that can synchronously reduce the greenhouse effect and convert solar energy into fuels. However, it is often limited by the intense light intensity required to produce high fuel production rates, and the catalyst deactivation due to severe carbon deposition generated from side reactions. Herein, a nanostructure of alumina-cluster-modified Ni nanoparticles supported on Al2O3 nanorods (ACM-Ni/Al2O3) was synthesized, displaying good catalytic performance under focused UV–vis-IR illumination. By light-driven thermocatalytic DRM on ACM-Ni/Al2O3 at a reduced light intensity of 76.9 kW m−2, the high fuel production rates of H2 (rH2, 65.7 mmol g−1 min−1) and CO (rCO, 78.8 mmol g−1 min−1), as well as an efficient light-to-fuel efficiency (η, 26.3 %) are achieved without additional heating. The rH2 and rCO of light-driven thermocatalysis are 2.9 and 1.9 times higher, respectively, compared to conventional thermocatalysis at the same temperature. We have discovered that high light-driven thermocatalytic activity originates from the photoactivation effect, significantly reducing the apparent activation energy and facilitating C* oxidation as a decisive step in DRM. ACM-Ni/Al2O3 possesses excellent durability and exhibits an extremely low coking rate of 4.40 × 10−3 gc gcatalyst−1 h−1, which is 26.8 times lower than that of the reference sample without Al2O3 cluster modification (R-Ni/Al2O3). This is owing to a decrease in activation energies (Ea) of C* oxidation and an increase in Ea of C* polymerization by the surface modification of Ni nanoparticles with Al2O3 clusters, effectively inhibiting carbon deposition.

Aqueous phase reforming of various compounds in biomass derived products over Ni/α-MoO3 catalysts: Effect of alkali and alkaline earth metals

Aqueous phase reforming (APR) of biomass derived products is a promising hydrogen generation approach, and many internal alkali and alkaline earth metals (AAEMs) have been proven capable of catalyzing these processes. In this study, APR of various functional groups in biomass derived products over Ni/α-MoO3 catalyst toward hydrogen production and pollutants control was investigated. The effect of different AAEMs was comprehensively studied under a temperature of 225 °C and a residence time of 30 min. Findings demonstrated that Na, K, Ca, and Mg all showed hydrogen generation and total organic carbon removal capability, whose performances were competitive to Ni/α-MoO3 catalyst. Moreover, although the presence of single K suppressed the removal of total nitrogen (TN), the combination of K and the Ni/α-MoO3 catalyst exhibited the optimal removal efficiency of TN (69.92 %). A series of characterization results revealed that the AAEMs effectively prevented Ni leaching in the hydrothermal environment of the Ni/α-MoO3 catalysts and promoted the formation of oxygen vacancies, inhibiting carbon deposition and deactivation of the catalyst.

Dry Reforming of Methane with Suppressed Carbon Deposition over Cr- and Ni-Loaded Dealuminated β Zeolites

Dry Reforming of Methane with Suppressed Carbon Deposition over Cr- and Ni-Loaded Dealuminated β Zeolites

Pollutant inhibition in an extreme ultraviolet lithography machine by dynamic gas lock

Dynamic gas lock (DGL) is an effective method to inhibit carbon deposition on optical surface in extreme ultraviolet (EUV) lithography machines. However, due to the complexity of the internal flow in DGL, relevant theoretical analyses remain incomplete. In this work, a direct simulation Monte Carlo (DSMC) method based on OpenFOAM platform is employed to study the transport process of rarefied gas in DGL and a project optics box (POB). The dsmcFoam + solver is extended and its applicability to DGL problems is verified. The results show that the number density of hydrocarbon in the POB decreases exponentially with the increase of the flow rate of clean gas, whereas the DGL inhibition rate is insensitive to the change of the pressure in the wafer chamber. Reducing the cone angle of the DGL, lowering the inlet position of the clean gas and using the clean gas with higher molar mass are all helpful to improve the inhibition effect of the DGL on the hydrocarbon diffusion. Additionally, the height of the DGL is relevant: with increase of the height, the inhibition rate rises at the same distance from the wafer surface; the number density of hydrocarbons is larger at higher heights. This study is expected to provide guidance for design of DGL technology under different EUV lithography conditions.

Mechanistic and microkinetic insights into the stability and activity of Ni3In catalyst for dry methane reforming

Dry methane reforming (DMR) reaction has garnered significant attention for its potential in consuming CO2 for environmental sustainability, as well as utilizing CH4 as a fossil resource with the highest hydrogen content. In-depth understanding the reaction mechanism with microkinetic modeling is essential for suppressing coke deposition and improving the stability of Ni catalysts. This study investigates the reaction intermediates and pathways of DMR on Ni3In alloy, which has been previously identified by theoretical high-throughput screening and experimental results as having improved resistance to carbon accumulation. Energetic profiles, determined through density functional theory calculations, reveal that the Ni3In catalyst exhibits an increased formation barrier for C* and lower adsorption strength compared to pure Ni catalyst. Microkinetic analysis using the CatMAP package demonstrates significantly lower carbon coverage on Ni3In than Ni catalysts. Importantly, the dissociation of CO2 plays a critical role in influencing the rate of CO formation, particularly at higher reaction temperatures. Furthermore, through flux analysis, we have identified the main reaction pathways for CO formation and highlighted the multiple pathways for oxidizing carbon-containing species to suppress carbon deposition on Ni3In catalyst. These findings not only provide theoretical support for the experimental stability of Ni-In catalysts but also offer valuable insights for the rational design of other Ni-based bimetallic catalysts employed in DMR reactions.

Experimental study on the mechanism of water on heat sink variation in catalytic partial steam reforming of supercritical n-decane

Regenerative cooling is an effective method for heat management of hypersonic vehicles and faces a problem of insufficient cooling capacity under higher flight Mach number. Water-assisted hydrocarbon fuels thermal conversion can effectively increase heat absorption and inhibit carbon deposition. The mechanism of water on the variation of heat sink is unclear. In this study, experimental study was conducted to investigate the effect of different water contents, pressure and mass flow rates on the variation of heat sink and the distribution of gaseous products in a continuous experimental system. The results show that catalytic partial steam reforming reaction consists of catalytic steam reforming and catalytic thermal cracking in the low temperature stage (T＜490 ℃), and non-catalytic thermal cracking is activated and gradually dominate in the high temperature stage (T＞490 ℃). The contribution of water to total heat sink is mainly caused by physical heat sink. Increasing mass flow rate mainly suppress the cracking reaction in the high temperature section by reducing reaction residence time. The flow rate has little effect on the chemical reaction equilibrium. Higher pressure has little effect on heat sink, but accelerates carbon deposition by promoting the formation of olefin products.

Study on the ablation of a pulsed plasma thruster with a non-volatile liquid propellant

Perfluoropolyether (PFPE), as a non-volatile liquid propellant for pulsed plasma thrusters (PPTs), has exhibited potential for inhibiting carbon deposition compared with polytetrafluoroethylene (PTFE). However, previous investigations have not focused on the ablation process of PPTs when using PFPE. In this study, ablation and the formation of carbon deposition were assessed based on ablated product analysis, element distributions, long-duration exposure images and emission spectroscopy. The results showed that the ablated products of PTFE were mainly CF and CF2, with a small amount of C, while PFPE was more likely to evaporate or generate molecules with large molecular weights. Carbon deposition on the ablated surface of PTFE was confirmed by the element distribution, while no obvious carbon deposition was found on the ablated surface of the porous ceramic. Carbon deposition was inevitable when using PTFE as a propellant according to the ablated products. The current density near the anode on the ablated surface of the propellant was low, and carbon could not be ablated in a timely manner; thus, carbon deposition easily occurred. For PFPE, the discharge arc was evenly distributed on the ablated surface, which could limit deposition.