Carbon Deposition Research Articles

High selectivity syngas generation by double perovskite oxygen carriers La2Fe2-xCoxO6 for chemical looping steam methane reforming

The generation of high-quality syngas combined with high-purity hydrogen is an essential challenge in the chemical looping steam methane reforming (CL-SMR) process, in which the design of oxygen carriers (OCs) is crucial. In this study, La2FeBO6 (BCr, Ni，Co) and La2Fe2-xCoxO6 (x = 0.2, 0.4, 0.6, 0.8, 1.0) double perovskites have been investigated as OCs in the CL-SMR process. Various analytical techniques (BET, XPS, XRD, H2-TPR, Raman.) have been deployed to characterize the OCs' specific surface area, crystal structure, and surface oxygen species. The fixed-bed experiments revealed that the Cr-modified perovskite had the lowest reactivity, which was attributed to the creation of LaCrO3 limiting the oxygen release rate of the OC. Meanwhile, Ni doping exhibited the maximum methane conversion (99.15 %), but it resulted in more carbon deposition due to methane cracking, and its carbon deposition was four times than that of Co doping. Whereas, the Co doped double perovskite OCs showed excellent overall performance, in which La2Fe1.8Co0.2O6 (L2F1.8Co0.2) exhibited the optimum CO selectivity (90.72 %), H2 selectivity (96.91 %), and H2 purity (96.84 %), as well as the lowest carbon deposition. Moreover, the L2F1.8Co0.2 also exhibited outstanding stability in 10 cycles, and it could be a prospective material for CL-SMR, enabling the simultaneous generation of high-quality syngas and high-purity hydrogen.

Plasma-catalytic dry reforming of CH4: Effects of plasma-generated species on the surface chemistry

By means of steady-state experiments and a global model, we studied the effects of plasma-generated reactive species on the surface chemistry and coking in plasma-catalytic CH4/CO2 reforming at reduced pressure (8–40 kPa). We used a hybrid ZDPlasKin-CHEMKIN model to predict the species densities over time. The detailed plasma-catalytic mechanism consists of the plasma discharge scheme, a gas-phase chemistry set and a surface mechanism. Our experimental results show that the coupling of Ni/SiO2 catalyst with plasma is more effective in CH4/CO2 activation and conversion than unpacked DBD plasma, with syngas being the main products. The highest total conversion of 16 % was achieved at 8000 V and 473 K, with corresponding CO and H2 yields of 15 % and 12 %, respectively. The reactants conversion and product selectivity are well captured by the kinetic model. Our simulation results suggest that vibrational species and radicals can accelerate the dissociative adsorption and Eley-Rideal (E-R) reactions. Path flux analysis shows that E-R reactions dominate the surface reaction pathways, which differs from thermal catalysis, indicating that the coupling of non-equilibrium plasma and catalysis can effectively shift the formation and consumption pathways of important adsorbates. For instance, our model suggests that HCOO(s) is primarily generated through the E-R reaction CO2(v) + H(s) → HCOO(s), while the hydrogenation reaction HCOO(s) + H → HCOOH(s) is the main source of HCOOH(s). Carbon deposition on the catalyst surface is primarily formed through the stepwise dehydrogenation of CH4, while the E-R reactions enhanced by plasma-generated H and O atoms dominate the consumption of carbon deposition. This work provides new insights into the effects of reactive species on the surface chemistry in plasma-catalytic CH4/CO2 reforming.

Predicting nickel catalyst deactivation in biogas steam and dry reforming for hydrogen production using machine learning

This study employs Random Forests (RF) and Artificial Neural Networks (ANN) to model the transient behavior of Ni catalyst deactivation during steam and dry reforming of model biogas containing H2S, with a focus on hydrogen production. Deactivation, induced by carbon deposition and sulfur poisoning, is a complex and transient phenomenon demanding precise kinetic mechanisms for accurately predicting Ni catalyst behavior in biogas reforming. Black-box machine learning (ML) models are developed, incorporating catalyst properties, biogas composition, and operating conditions. Encompassing both dry and steam reforming, the ML models aim to predict catalyst behavior, expressed in terms of packed bed reactor exit mole fractions (H2, CO, CH4, and CO2) and conversions (CH4 and CO2). The ML models are trained and tested across a temperature range of 700–900 C with 0–145 ppm of H2S in model biogas (CH4/CO2 ratio varying from 1.0 to 2.0). RF outperforms the ANN across all performance metrics, including overall R2 and root mean squared error (RMSE). The RF achieves a mean overall R2 of 0.979, with training and testing RMSE equal to 6.7×10−3 and 1.47×10−2 respectively. In contrast, the ANN achieves a mean overall R2 of 0.939, with training and testing RMSE equal to 2.6×10−2 and 2.55×10−2 respectively. Moreover, pre-trained RF models are validated with unseen data of dry reforming of biogas containing 30 ppm of H2S (25 data points). It is suggested that 35 % of this unseen experimental data is required to train the RF model for it to predict catalyst deactivation, achieving a validation R sufficiently2> 0.9. The mean overall R2 values attained by the RF fine-tuned on 35 % of the unseen experiment data for both CH4 and CO2 conversions, as well as for all mole fraction predictions, are 0.952 and 0.948, respectively.

Influence of gamma radiation on the composition and physicochemical characteristics of olefins: post-radiation effects

The effect of gamma radiation on olefins was studied under static conditions at an absorbed dose of 65 kGy and at a dose rate ofP= 0.076 Gy/s. The effect of radiation on the physicochemical characteristics and structural and group composition of the resulting olefins has been established. Post-irradiation effects were studied immediately after irradiation and during 1, 2, 4, and 7 months later. When fuels are irradiated, polymerization of unsaturated hydrocarbons occurs. After cessation of irradiation, the postpolymerization process occurs The chemical instability of olefins in fuels leads to the formation of carbon deposits in the engine system, tanks, and valves. IR spectra, iodine values, density, and kinematic viscosity of irradiated samples were measured.

The catalytic decomposition of CH4 using Ce-doped Fe/CaO-Ca12Al14O33 catalyst and its regeneration performance for H2 production

The catalytic decomposition of CH4 using low cost and non-toxicity Fe-based catalysts is a prospective method for H2 production. The regeneration process of iron-based catalysts involves CO2 emission and incomplete conversion of carbon deposition. In this work, a novel catalytic decomposition of CH4/regeneration process was proposed using the Ce-doped Fe/CaO-Ca12Al14O33 catalyst for H2 production. To remove the carbon deposition in the catalyst, the regeneration stage includes four steps: solid carbon production by vibratory separation, steam gasification of residual carbon deposition to produce H2 where CO2 is captured by CaO to form CaCO3, calcination of CaCO3 to produce CaO and pure CO2, methanol production by CO2 and H2 from carbon deposition gasification. The effects of Ce doping on the catalysis/regeneration performance of Fe/CaO-Ca12Al14O33 catalysts were studied, and the Ce-doped Fe/CaO-Ca12Al14O33 catalyst was compared with Cu-, Zn-, and Mn- doped Fe/CaO-Ca12Al14O33 catalysts. The solid carbon obtained from the catalytic decomposition of CH4/regeneration cycles was characterized. The Ce-doped Fe/CaO-Ca12Al14O33 catalyst shows excellent catalysis, CO2 capture, and stability performance in the catalytic decomposition of CH4/regeneration cycles. The average CH4 conversion is 90.02% in the first cycle, which decreases to 80.01% after 8 cycles. Carbon nanotubes are the main forms of obtained solid carbon with the favorable pore structure. The doping of Ce improves the effective adsorption sites for CH4 and CO2. Carbon deposition in the catalyst is efficiently removed by steam gasification. In addition, CeO2 promotes the electron transfer, oxygen vacancy generation, and Fe3C decomposition, which leads to superior catalytic performance and resistance to deactivation of the catalyst. The CeO2-doped Fe/CaO-Ca12Al14O33 catalyst is promising for H2 production via catalysis/regeneration cycles.

In-situ exsolved Ni nanoparticles for boosting CO2 reduction in solid oxide electrolysis cell

Due to their excellent high Faraday efficiency, perovskite solid oxide cells (SOECs) have attracted considerable attention. Nevertheless, they still face significant challenges in terms of stability and electrocatalytic activity during CO₂ electrolysis. In this study, Ni particles in La0.65Ba0.35Mn1-xNixO3-δ are successfully separated by a unique in-situ exsolved method of metal nanoparticles, which are uniformly anchored to the electrode surface as Ni nanometal particles. This effectively suppresses the generation of carbon deposits on the cathode surface. Under test conditions of 850 °C, 1.6 V and 50 sccm flow rate, the CO yield of the modified cathode material reached 5.9 mL min−1 cm−2, which is nearly four times higher than that before doping. The synergistic effect of in-situ exsolution of Ni metal nanoparticles with oxygen defects generated by the perovskite, creating more active locations for CO2 adsorption and electrolysis, is responsible for the significant improvement in electrochemical performance. This work provides new strategies and ideas for the development of efficient and durable SOEC cathode materials.

Manipulation of Mn/Ce ratio for deep chlorobenzene oxidation: Catalytic mechanisms and byproducts analysis

In this research, a sequence of spatial porous MnCeOx catalysts with varying Mn/Ce from 3:1 to 1:7 were synthesized using the sol–gel method for chlorobenzene (CB) oxidation. Mn1Ce1 exhibited the best performance due to its high lattice oxygen content and the strong interaction between Ce and Mn. The increase in Mn content in CeO2 catalysts resulted in enhanced redox properties and acidity, which was beneficial for the adsorption and activation of CB, thus enhancing the selectivity and the desorption of HCl on the catalyst surface. Carbon deposition and the formation of metal chloride were the main reasons for catalyst deactivation. At low temperature regions (150 ∼ 300 °C), insufficient oxidation capability and the chlorine deposition on the catalyst surface resulted in the formation of various chlorinated compounds. As the temperature increases (300 ∼ 450 °C), the release of HCl and more reactive oxygen species is available on the catalytic interface, generating various oxygen-containing degradation intermediates. This work proposed a fine-designed, low-cost mixed metal oxide catalysts for low temperature CB oxidation, and provided novel in-depth understandings of degradation intermediate formation thermodynamics. Our findings would be helpful for deep purification of chlorinated VOCs polluted industrial tail gas.

Renewable Zn/S-1 catalyst with dual active sites for acetylene acetoxylation

The prevailing Zn/AC catalysts was plagued by limited lifetime and difficulties in regeneration for acetylene acetoxylation. In order to exploring renewable catalyst for acetylene acetoxylation, Zn/S-1 catalyst was synthesized using Silicalite-1(S-1) as support. The catalytic performance of Zn/S-1 was compared with Zn/AC catalyst using active carbon as support. The CH3COOH conversion of Zn/S-1 catalyst only decreased 15 % after running 225 h, much better than the 66 % of Zn/AC after 154 h. TG analysis revealed that the improved stability of Zn/S-1 catalyst was attributed to its better resistance for carbon deposition with the presence of S-1 support. A series of characterizations and DFT results elucidated that the Lewis acid sites of S-1 support and Zn component serve as dual active sites, which enhanced the adsorption of CH3COOH and inhibited the carbon deposition. In addition, the deactivated Zn/S-1 catalyst could be regenerated by calcination in air atmosphere due to the thermal stability of S-1, and the regenerated Zn/S-1 catalyst showed similar catalytic activity with the fresh catalyst.

PEG-assisted synthesis of highly dispersed Cs/Zr-SiO2 catalyst for aldol condensation of methyl acetate with formaldehyde

The dispersion of active sites plays an imperative role in the promotion of catalytic performance on methyl acrylate synthesis via direct vaporous aldol condensation. Herein, a novel PEG-assisted impregnation method was proposed to synthesize Cs/Zr-SiO2 catalyst with high dispersion of acid and base sites. A series of characterization techniques including NMR, TEM, physical N2 adsorption isotherms, XRD, XPS, NH3-/CO2-TPD, and Py-IR were used to investigate the physico-chemical properties of these prepared catalyst series. The introduction of PEG improved the specific surface area, dispersion of active sites, and density of acid and base sites, resulting in superior catalytic performance of Cs/PEG@Zr-SiO2 by comparison with that of Cs/SiO2 and Cs/Zr-SiO2. The kinetic experiments revealed that the activation energy of aldol condensation was 80.8 kJ/mol over the Cs/PEG@Zr-SiO2 catalyst. The deactivation behavior derived from carbon deposition was discovered, and the spent catalyst could be regenerated by simple thermal treatment.

Preparation of high temperature proton exchange membranes with multilayered structures through alternate deposition of carbon dots@Metal organic framework and Sulfonated Poly(Ether Ketone)

High temperature proton exchange membranes (HTPEMs) with multilayered structures based on carbon dots@metal organic framework (CDs@MOF) and Sulfonated Poly(Ether Ketone) (SPEEK) have been prepared with the spin coating technique. In this research, carbon dots (CDs) are self-assembled with metal organic framework (MOF) to form the composite of CDs@MOF. Successive proton conduction channels consisting of CDs@MOF and sulfonated groups in SPEEK facilitate to conduct protons in multilayered structures of the prepared composite membranes. Additionally, CDs@MOF can combine phosphoric acid (PA) molecules deriving from the formed intermolecular hydrogen bonding. The proton conductivity is further improved because of the multilayered structures reducing the proton conduction resistance. Specifically, the (SPEEK/40%CDs@MOF)3/PA membrane exhibits the maximum proton conductivity of (5.02 ± 0.64) × 10−2 S/cm at 160 °C. Notably, the proton conductivity can retain 1.53 × 10−2 S/cm at 80 °C after a 200 h non-stop test. The open circuit voltage peak and power density of a single fuel cell based on the (SPEEK/40%CDs@MOF)3/PA membrane respectively reach 0.95 V, 258.2 mW/cm2 at 100 °C and 0.96 V, 369.9 mW/cm2 at 120 °C.

Influence of the Interaction of Nickel and Copper with Ceria on Ethanol Steam Reforming over Ni-Cu-CeO2 Catalysts

Catalysts of nickel-ceria, nickel-copper-ceria, and copper-ceria were explored with respect to their properties for hydrogen production through ethanol steam reforming (ESR). They were prepared by coprecipitation of the components within inverse microemulsions to achieve intimate contact between them, and the catalysts were characterized by N2 adsorption measurements, XRD, Raman spectroscopy, TPR, and XPS. The catalysts were tested for the ESR reaction, and they were regenerated with oxygen when significant deactivation took place, as occurred for the copper-containing systems. In contrast, the nickel–ceria catalyst exhibits a high activity and stability despite the formation of an important amount of carbon deposits during the course of the ESR test. The presence of nickel sites, which strongly interact with the ceria support, and which are affected by the presence of copper, and the limitation of copper for C-C bond breaking are invoked to explain the results obtained on the whole.

Effect of Temperature on the Growth Rate of Carbon Nanotubes (CNTs) using Electrodeposition Method

Electrodeposition is one of the carbon capture methods used to produce carbon nanotubes with temperature as one of the variable. The research aims to analyze the effect of temperature on the growth rate of carbon nanotubes of 723oC, 750oC, 800oC, 850oC and 900oC using X-Ray Diffraction (XRD) testing. Analyzing deposit morphology at the same temperature using Scanning Electron Microscope (SEM) testing. The results of research show that the most optimal growth rate for carbon nanotubes occurred at 750oC of 7,949 g cm-2 hours-1. At a temperature of 750oC, carbon deposits are easier than at 723oC because that’s the melting point of lithium carbonate and has not completely decomposed. The XRD test show that at 750oC is the highest peak at 2θ= 26.21o. The SEM test show that the optimal morphological structure formed occurs at a temperature variation of 750oC with a fibrous morphology and little impurity at the ends. The results of the CNT percentage using the Material Analysis Using Diffraction (MAUD) method show that the largest quantitative value of the CNT percentage occurs at a temperature of 800oC of 4.08%.

Insights into the effect of Fe-Zn interaction on tunable reactivity in Fischer–Tropsch synthesis

In the Fischer–Tropsch synthesis (FTS) reaction, the intricate reaction conditions are prone to induce phase transitions in iron carbides, which markedly affect catalytic performance. Manipulating and stabilizing the active phase is paramount for ensuring the catalyst efficiency. In this study, we regulated the Fe-Zn interaction to investigate the influence of iron carbides and the characteristics of surface carbon species. The strong interaction significantly enhanced the adsorption and dissociation of CO on the catalyst surface, thereby facilitating the formation of carbon-rich Fe2(.2)C. Consequently, the FeZn-s catalyst exhibited the highest iron time yield (FTY) of 959 μmolCO·gFe-1·s-1. But meanwhile, the stronger Fe-Zn interaction also accelerated the carbon deposition rate and elevated the graphitization degree of the surface carbon, expediting the catalyst deactivation. These results provide an insight into the modulation and stabilization of iron carbides by adjusting the interaction between the Fe and supports, which inspires the further development of Fe-based catalysts for FTS applications.

Photosynthetic and Carbon Sequestering Ability of Safflower Leucea and Accumulation of Organic Carbon in Sod-Podzolic Soil

According to the content of photosynthesis pigments, the most active period of photosynthetically active radiation absorption by the leaves of Leucea safflower during the growing season was revealed. From the moment of full regrowth to flowering, the amount of chlorophylls a and b in the leaves was 6.2–8.5 mg/g of dry weight, carotene – 3–4 times less. During photosynthesis, the carbon content in the leaves of Leucea safflower practically did not change and amounted to 39.5–42.5%. The mass fraction of the main product of photosynthesis, sugars, increased from the regrowth phase to seed formation from 4.0 to 11.8%. During the period of active growth, the nitrogen content in the leaves of the leucea was 1.3–1.6, phosphorus – 1.1–1.6, potassium – 4.4–5.1%. After harvesting the safflower leucea of the 14th year of life, a high amount of сrop and root residues (CRR) was determined in the sod-podzolic soil – 13.7–17.3 t/ha. The amount of carbon absorbed during photosynthesis was 6.8–11.5 t C/ha (24.3–41.3 t CO2/ha), depending on the experiment variant, for natural phytocenosis this indicator was equal to 2.4 t C/ha (or 8.6 t CO2/ha) during the growing season. The organic carbon content under the safflower leucea of the 14th year of life in the 0–20 cm soil layer increased relative to the initial level by 3.6% in the version without fertilizers, by 15.1% in the N60P60K60 variant, and in the 20–40 cm layer by 8.8–42.6%, respectively. Relative to the virgin analogue, the carbon content in the 0–20 cm layer was 15.2–28.0 higher, in the 20–40 cm layer – 25.0–64.4%, depending on the experiment variant, which indicated the deposition of carbon in the form of humic substances due to its storage in deeper soil layers.

The Coking of a Solid Catalyst Rationalized with Combined Raman and Fluorescence Lifetime Microscopy.

The formation of carbon deposits is a major deactivation pathway for solid catalysts. Studying coking on industrially relevant catalysts is, however, often challenging due to the sample heterogeneity. That is especially true for zeolite-containing catalysts where fluorescence often hampers their characterization with Raman spectroscopy. We turned this disadvantage into an advantage and combined Raman and fluorescence (lifetime) microscopy to study the coking behavior of an equilibrium catalyst material used for fluid catalytic cracking of hydrocarbons. The results presented illustrate that this approach can yield new insights in the physicochemical processes occurring within zeolite-containing catalyst particles during their coking process. Ex situ analyses of single catalyst particles revealed considerable intra-sample heterogeneities. The sample-averaged Raman spectra showed a higher degree of graphitization when the sample was exposed to more hexane, while the sample-averaged fluorescence lifetime showed no significant trend. Simultaneous in situ Raman and fluorescence (lifetime) microscopy, used to follow the coking and the regeneration of single particles, gave more insights in the changing fluorescence dynamics. During the coking, the rise and decline of the average fluorescence lifetime suggested the prolonged presence of smaller coke species that are quenched more and more by adjacent larger polyaromatics acting as Förster-resonance-energy-transfer acceptors.

Self-regenerative Ni/SiO2 for dry reforming of methane (DRM): 1000 h-longevity assessment and operando insights to coke removal under N2 atmosphere

Commercializing Ni-catalyst for dry reforming of methane (DRM) has yet to be realized due to two known issues: catalyst sintering and carbon deposition. Significantly, our developed tremella-like Ni/SiO2 has previously demonstrated outstanding resilience against sintering under prolonged heat exposure. The carry-on investigation herein further showcases its interesting self-regenerative behavior, which enables carbon removal and full activity restoration under inert N2-blanket. Better still, the resultant N2-regenerated Ni/SiO2 can immediately re-apply to DRM, contrasted to the traditional oxidative-regenerated counterpart that mandated intermediate reduction process for catalyst re-activation. Characterization results indicate that an appreciable portion (32.05 %) of deposited Ni (7.3 wt%) is reducible into active metallic phase; however, only 1.233 % of them are resided on the surface of Ni/SiO2 and involved in DRM. Despite such low involvement rate, >90 % CO2 and CH4 conversion could still be attained initially, reasonably due to the morphological prominence of the catalyst. Longevity experiment confirmed the adequacy of intermittent N2-regeneration in removing deposited carbonaceous, mechanistically assisted by the labile O-atom migrated from SiO2 support. Upon 4 h N2-regeneration, thorough activity restoration of Ni/SiO2 can be facilely realized, thereafter sustaining DRM for 1000 h with CO2 conversion controlled at > 78 %. The results herein provide important insights to DRM community, where the demonstrated N2-self-regeneration process promises a reduction-free, time- and cost-saving solution to DRM catalysts beyond Ni/SiO2.

Influence of the Acetylene Flow Rate and Process Pressure on the Carbon Deposition Behavior by Thermal Chemical Vapor Deposition Process

We used the chemical vapor deposition process to deposit carbon film at a high temperature (900 °C). The carbon films were deposited on AISI 1006 foils using an acetylene gas. We analyzed the carbon film deposited on the surface using Raman spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy to define changes in the bonding structure of the carbon film. The results of Raman spectroscopy and high-resolution transmission electron microscopy revealed that as the acetylene flow rate increased, the shape of the deposited carbon film changed from graphene to graphite. In addition, in order to compare the quality of the carbon film in terms of mechanical and electrical properties, carbon films treated under various conditions were closely analyzed using nano-indenter and a sheet resistance meter. Therefore, the optimal condition (1 Torr-50 sccm) was selected in which graphene was uniformly deposited and had the lowest electrical resistance (500 Ω/sq) and highest hardness (12 GPa).

Amorphous Carbon Nitride Films: Surface and Subsurface Composition and Bonding.

To obtain quantitative information about the composition and bonding of atoms located at and beyond the analyzed solid surface nondestructively, we applied angle-resolved X-ray photoelectron spectroscopy aided by the maximum entropy method to air-exposed amorphous carbon nitride films deposited by pulsed laser deposition of diamond-like carbon modified by low-energy nitrogen ion bombardment during film growth. We demonstrate that the composition, chemical bonding, and mass density vary significantly from the top surface to a shallow subsurface region. The analyzed samples, in a shallow surface region of ∼1 nm, are composed of oxygen, nitrogen, hydrogen, and mostly carbon in sp2 hybridization. In a deeper region, the C sp3 content increases substantially going to a maximum, whereas the nitrogen percentage decreases to a minimum, then increases, and tends to saturate. Special attention has been paid to in-depth distributions of carbon atoms in trigonal and tetragonal arrangements because they specify numerous physical and chemical properties of carbon-based materials. These results indicate that the interaction of DLC:N surfaces with surroundings can be influenced, barring oxygen and nitrogen, by sp2-bonded carbon atoms located near the surface of the samples. The obtained results can be useful for developing a deeper understanding of the interaction between DLC:N layer surfaces and their surroundings and particularly with living tissue.

Effect of ash-bridge deposition in asymmetric diesel particulate filter channels on the pressure drop and particulate matter trapping characteristics

A diesel particulate filter (DPF) is commonly used to trap particulate matter (PM). The collapse and sintering of carbon and ash deposits during exhaust gas flow and DPF regeneration frequently result in the formation of ash bridges, which are buildups of ash and PM that clog the filter channels. To investigate the impact of an ash bridge formed by accumulated ash on the pressure drop and PM trapping characteristics of asymmetric DPFs, an asymmetric DPF channel with an ash bridge was constructed. The analysis employed computational fluid dynamics to examine how the ash bridge affects the pressure drop and PM trapping characteristics in an asymmetric DPF. This study reveals that the asymmetric DPF design effectively enhances the ash-holding capacity, thereby mitigating the risk of channel blockage. The presence of ash bridges in DPF channels has a more substantial impact on the pressure drop through radial congestion than through axial congestion. The application of asymmetric thin-wall DPFs can counteract the increase in exhaust backpressure caused by ash bridges. An ash bridge located in the middle of a DPF channel intensifies the uneven deposition of PM. However, implementing an asymmetric DPF structure enhances the uniformity of PM deposition.

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.