Anti-coking Properties Research Articles

The effect of hydrothermal pretreatment on the catalytic performance of Zn/HZSM-5 catalysts for ethylene aromatization reaction

To address the issue of coking and deactivation of Zn/HZSM-5 catalysts used for lightolefins aromatization, a high-temperature hydrothermalmethod was employed for catalyst pretreatment. The catalysts were characterized using XRD, N2 physical adsorption-desorption, NH3-TPD, Py-FTIR, XPS, and TG techniques. The effect of high-temperaturehydrothermal pretreatment on the catalytic performance and stability of the catalyst was investigated using ethylene aromatization as a probe reaction. The results showed that the Zn/HZSM-5 catalyst exhibited excellent catalytic performance after48 h of high-temperature hydrothermal pretreatment. Although the conversion of ethylene slightly decreased, the catalyst lifetime was significantly extended, increasing from 72to 216 h, while the aromatics selectivity remained above 60%. It was suggested that the hydrothermal treatment enhanced the interaction between ZnO species and Brønsted acid sites, promoting the generation of ZnOH+ species. This not only suppressed the hydrogen transfer reaction but also significantly enhanced the dehydrogenation performance of the catalyst, improving the selectivity towards hydrogen. Additionally, the catalyst exhibited increased carbon capacity and reduced carbon deposition rate after hydrothermal treatment, demonstrating excellent anti-coking properties.

MOF-derived carbon-based catalysts with enhanced anti-coking property for the dry reforming of methane

To avoid sintering and carbon deposition of conventionally loaded catalysts, a spatial confinement strategy was employed to design a high-performance catalyst for the dry reforming of methane (DRM) reaction. With tri-metallic Ni-Co-Mg metal-organic framework (MOF-74) as a precursor, a novel nanostructured NiCoMg@C catalyst was synthesized, where the active metals Ni and Co were confined within the carbon framework derived from MOF pyrolysis. Characterization results indicate that the catalyst synthesized with MOF as template has a high specific surface area, well-dispersed metals, and strong metal-support interactions. The introduction of a high content of Mg promoted the dispersion of active metal Ni and Co and increased the number and strength of surface basic sites. Among the catalysts, NiCoMg20@C exhibited optimal catalytic activity, with initial CH4 and CO2 conversion rates reaching 75.13 % and 85.29 %, respectively. More importantly, the catalyst showed high stability during 100 h DRM reaction at 700 °C without significant carbon deposition. This research provides a new perspective for the development of DRM catalysts.

Surface basic site effect on CoLa/m-Al2O3 catalysts for dry reforming of methane

Dry reforming of methane (DRM) is a novel technology that enables the direct utilization of greenhouse gases (CH4 and CO2) for the production of value-added products. In the DRM reaction, the acid-base characteristics of the catalyst support play a pivotal role in determining the performance of the catalyst. In this study, a series of Co-based catalysts with different alkali earth metal-modified Al2O3 composite supports, specifically m-Al2O3 (m=Ca, Mg, and Ba), were prepared using the impregnation method. Various characterization techniques were employed to investigate the impact of alkaline site modulation on the support surface with respect to anti-sintering and anti-coking properties. The results demonstrate that the m-Al2O3 composite support catalysts, prepared with Mg and Ca modulation, exhibit an abundance of basic sites and oxygen vacancies. This promotes the adsorption and activation of CO2, enhances the rate of carbon elimination, and effectively addresses carbon deposition and metal sintering issues. Notably, the CoLa/Mg-Al2O3 catalyst shows the highest performance under reaction conditions of 750 °C, with CH4 and CO2 conversions reaching 92.3 % and 97.5 %, respectively. On the other hand, the CoLa/Ba-Al2O3 catalysts display poor performance in dry reforming. Kinetic studies indicate that CoLa/Mg-Al2O3 catalyst significantly reduce the apparent activation energy required for CH4 and CO2 cracking. Furthermore, it is demonstrated that the introduction of alkali earth metals can promote the dissociation of CH4 and CO2.

The Pivotal Roles of Light and Ca‐Doping in Photothermocatalytic CO2 Reduction by Methane on Nanocomposites of Nickel Nanoparticles Loaded on Ca‐Doped Al2O3

CO2 and CH4 are greenhouse gases that can be converted into H2 and CO through light‐driven photothermocatalytic CO2 reduction with methane (CRM), which is a process of solar energy collection and storage. However, conventional catalysts require high light intensities (≥192.0 kW m−2) to obtain high fuel reaction rates and solar‐to‐fuel efficiency (η), and deactivate easily to coking at high temperature. Herein, a nanomaterial of Ni nanoparticles loaded on Ca‐doped Al2O3 (Ni/Ca–Al2O3) is synthesized. Ca doping improves the CO2 adsorption capacity of Ni/Ca–Al2O3. Under focused ultraviolet–visible–infrared illumination at low light intensity (80.8 kW m−2), Ni/Ca–Al2O3 obtains high production rates of H2 (, 76.85 mmol min−1 g−1) and CO (rCO, 90.90 mmol min−1 g−1), which are 1.9 and 1.3 times of those in the dark respectively, and exhibits a large η (30.3%) and good stability. The coking rate of Ni/Ca–Al2O3 is reduced by a factor of 25.8 compared to the reference catalyst with Ni nanoparticles loaded on Al2O3. The improvement of catalytic activity and anticoking properties stems from the photoactivation, which not only accelerates the CRM on Ni nanoparticles, but also enhances the oxidation of carbon species (produced on Ni nanoparticles) through strong adsorption of CO2 on Ca–Al2O3 at Ni/Ca–Al2O3 interface.

Construction of highly stable and efficient Zn-based catalyst via Mg modification for propane dehydrogenation

Zn-based catalysts are considered a kind of efficient catalysts for propane dehydrogenation (PDH) because of their low price and non-toxicity. However, Zn-based catalysts still face problems such as the limited diffusion of reaction gas, non-uniform distribution of Zn species, and easy coking. Here, a novel double-layered silicalite-1 (DS-1) support with high specific surface area was synthesized by a crystal growth method, and an alkaline additive modification strategy has been adopted to prepare the Mg-modified Zn-based catalyst (0.1Mg5Zn@DS-1) in order to improve the catalytic activity and stability. The physical characterization results reveal that the Mg modification induces the enhanced electronic interactions between Zn sites and Mg species. Besides, the modified Mg species also reduce the Lewis acidity, allowing easier desorption of propylene and improving the propylene selectivity with anti-coking property. Furthermore, PDH evaluation results demonstrate that the optimal 0.1Mg5Zn@DS-1 catalyst achieves the propylene yield of ∼44 %, propylene selectivity of ∼95 % as well as outstanding stability and regeneration ability. This work provides a novel insight into the design of Zn-based catalysts with high activity and excellent stability.

Boosting the performances of protonic solid oxide fuel cells for co-production of propylene and electricity from propane by integrating thermo- and electro- catalysis

Protonic solid oxide fuel cells (p-SOFC) integrated with clean thermal energy sources are promising platforms for decarbonized chemical production in addition to power generation, such as on-purpose propylene production from propane dehydrogenation (PDH). The catalytic performance of the conventional nickel-cermet-based anode materials in p-SOFC for propane conversion is restrained by their low active surface area and proneness to coking. In this work, by integration of a highly efficient industry-relevant thermal catalyst PtGa/ZSM-5 for PDH reaction, we demonstrate that both the electrochemical and catalytic performance of the propane-fueled p-SOFC can be effectively enhanced. The PtGa catalyst integrated p-SOFC exhibits a peak power density of 93 mW cm−2 at 600 °C, which is greater by about 100% and 50% than that without catalyst or with a perovskite-based (Pr0.3Sr0.7)0.9Ni0.1Ti0.9O3 (PSNT) catalyst layer, respectively. The PDH activity and olefin selectivity of the PtGa catalyst is also significantly higher than that of the PSNT catalyst. In addition, much improved coke tolerance and propylene selectivity (over 90%) compared to the catalyst-free Ni-cermet anode materials were achieved by integrating the industrial catalyst layer. The propane conversion can be further improved by an applied current density, whereas the olefin selectivity is almost unaltered. The excellent performance of the PtGa catalyst integrated p-SOFC is attributed to the high surface area, intrinsically high catalytic activity, selectivity, and anti-coking properties of the catalytic layer for propane conversion. This work provides a general approach and a case study for boosting the performances of p-SOFCs in chemical production by integrating thermo- and electro- catalysis.

Insight into the role of preparation method on the structure and size effect of Ni/MSS catalysts for dry reforming of methane

Dry reforming of methane (DRM) is considered a promising process to convert CH4 and CO2 into syngas for achieving carbon neutrality. However, sintering and carbon deposition of Ni pose significant challenges to the industrialization of DRM. The size of Ni particles significantly affects the generation of carbon deposits. In this study, a series of Ni/MSS catalysts were prepared using four different methods, including common impregnation, glycine-assisted impregnation, ethylene glycol-assisted impregnation and ammonia evaporation. The effects of preparation methods on the anti-sintering and anti-coking properties were explored through various characterization techniques. Results showed that glycine-assisted impregnation and ethylene glycol-assisted impregnation effectively improved the dispersion of Ni, resulting in small Ni particles while preserving the unique pore structure of MSS supports. Smaller Ni particles expose more active sites, which facilitate the resistance to carbon accumulation. These catalysts show the highest activity and excellent stability. The catalyst prepared by ammonia evaporation showed the best stability due to the synergistic effect of the strongest basicity and metal-support interaction. However, nickel phyllosilicate generation consumed a small amount of MSS, resulting in reduced specific surface area. Compared with the common impregnation method, the other three methods reduced the particle size of Ni and improved the interaction between support and metal, effectively enhancing the ability of the catalyst to resist coking and sintering. Kinetic studies also showed a significant decrease in the apparent activation energy of methane and carbon dioxide cracking due to the reduced particle size of Ni particles.

Investigating the promotion of Fe–Co catalyst by alkali and alkaline earth metals of inherent metal minerals for biomass pyrolysis

The alkali and alkaline earth metals (AAEMs) in the inherent metallic minerals of biomass have a crucial effect on the pyrolysis process. In our previous work, the experiments mainly investigated the effects of Fe–Co catalysts on pine needle (PN) pyrolysis. This work further explored the synergistic effect of AAEMs (K, Ca, Na, and Mg) with Fe–Co-catalyzed biomass pyrolysis. The results showed that AAEMs in biomass could improve the gas yield by promoting decarbonization, decarboxylation, and hydrocarbon conversion. Adding Co to Fe enhanced the stability and anti-coking properties of the catalyst, which facilitated the breakage of C–H/C–C bonds and the conversion of oxygenated compounds to hydrocarbons, increasing the H2 yield (13.99 mL/g → 92.50 mL/g). AAEMs enhanced the catalytic activity of Fe–Co catalysts with high selectivity for H2 (92.50 mL/g→104.81 mL/g) and CO (65.00 mL/g→73.65 mL/g). The characterization results showed that AAEMs promoted the reduction of Fe–Co catalyst and the dispersion of metal active sites, which facilitated the transition from disordered to ordered carbon and the removal of oxygen functional groups such as O–H, thus increasing the CO yield, while the effective cleavage of CH4 and C2 compounds and the dehydrogenation of organic components promoted the increase of H2 yield, and the activity followed Na > Ca > Mg > K.

Pivotal Role of Ni/ZrO2 Phase Boundaries for Coke-Resistant Methane Dry Reforming Catalysts

To identify the synergistic action of differently prepared Ni-ZrO2 phase boundaries in methane dry reforming, we compared an “inverse” near-surface intermetallic NiZr catalyst precursor with the respective bulk-intermetallic NixZry material and a supported Ni-ZrO2 catalyst. In all three cases, stable and high methane dry reforming activity with enhanced anticoking properties can be assigned to the presence of extended Ni-ZrO2 phase boundaries, which result from in situ activation of the intermetallic Ni-Zr model catalyst systems under DRM conditions. All three catalysts operate bifunctionally; methane is essentially decomposed to carbon at the metallic Ni0 surface sites, whereas CO2 reacts to CO at reduced Zr centers induced by a spillover of carbon to the phase boundaries. On pure bulk Ni0, dissolved carbon accumulates in surface-near regions, leading to a sufficiently supersaturated state for completely surface-blocking graphitic carbon segregation. In strong contrast, surface-ZrO2 modified bulk Ni0 exhibits virtually the best decoking and carbon conversion conditions due to the presence of highly dispersed ZrO2 islands with a particularly large contribution of interfacial Ni0-ZrO2 sites and short C-diffusion pathways to the latter.

Promotion effect of different lanthanide doping on Co/Al2O3 catalyst for dry reforming of methane

In this paper, a series of cobalt catalysts modified by different lanthanide metals were synthesized via co-impregnation method using inexpensive industrial-grade alumina as a support for dry reforming of methane. The effect of lanthanide metals as accelerators of cobalt-based catalysts on catalytic performance and anti-coking properties was mainly investigated. The textural relationships between the catalytic performance and physicochemical properties of cobalt-based catalysts doped with different lanthanide metals were further investigated. Different characterization techniques demonstrate the positive effect of lanthanide metals on the physicochemical properties of catalysts. The results show that the electron transfer between cobalt species and lanthanide metal oxides is significantly enhanced due to the introduction of lanthanide elements. The process generates more active sites, which is favorable for the adsorption and activation of methane. In addition, the abundant medium basic sites and oxygen vacancies on the surface of cobalt-based catalysts with the effect of lanthanides promoted the adsorption and activation of carbon dioxide and the gasification of carbon accumulation, which greatly improved the anti-carbon accumulation performance of the catalysts. Therefore, the prepared cobalt-lanthanum-based catalysts showed the best catalytic effect and have great potential for application.

Hydrogen Production through Bi-Reforming of Methane: Improving Ni Catalyst Performance via an Exsolution Approach

Hydrogen production through the bi-reforming of methane over exsolution-derived Ni catalysts has been studied. Nickel-based catalysts were prepared through the activation of (CeM)1−xNixOy (M = Al, La, Mg) solid solutions in a reducing gaseous medium. Their performance and resistance to coking under the reaction conditions were controlled by regulating their textural, structural, morphological, and redox properties through adjustments to the composition of the oxide matrix (M/Ce = 0–4; x = 0.2–0.8; y = 1.0–2.0). The role of the M-dopant type in the genesis and properties of the catalysts was established. The efficiency of the catalysts in the bi-reforming of methane increased in the following series of M: M-free < La < Al < Mg, correlating with the structural behavior of the nickel active component and the anti-coking properties of the support matrix. The preferred M-type and M/Ce ratio determined the best performance of (CeM)1−xNixOy catalysts. At 800 °C the optimum Ce0.6Mg0.2Ni0.2O1.6 catalyst provided a stable H2 yield of 90% at a high level of CO2 and CH4 conversions (>85%).

Anti-coking NiCex/HAP catalyst with well-balanced carbon formation and gasification in methane dry reforming

Methane dry reforming (MDR) is a promising process to convert two major greenhouse gases into syngas. However, the major drawback of the process is the deactivation of Ni-based catalysts due to carbon deposition and metal sintering. Herein, we prepared hydroxyapatite (HAP) supported Ni catalysts modified by CeO2, which can efficiently promote MDR reaction with the excellent anti-coking property. The strong interaction between Ni and HAP guarantees the stability of highly dispersed Ni particles during the MDR reaction. The neighboring CeO2 over Ni particles could facilitate the mobility of oxygen, which assists the activation of CH4 to CH3O and in some extent hinders the deep cracking of CH4 into deposited carbon. Meanwhile, the kinetic studies indicate that the existence of reactive oxygen species is beneficial for enhancing carbon gasification. Accordingly, the addition of CeO2 balanced the carbon formation and gasification over Ni and therefore efficiently prevented coke accumulation. The exploration of NiCex/HAP catalysts would provide inspiration for future MDR catalyst design.

Synergistic modification of Ca/Co on Ni/HZSM-5 catalyst for pyrolysis of organic components in biomass tar

This study used ultrasonic-assisted over-impregnation method to prepare Ni/HZSM-5 catalysts modified by Ca/Co for pyrolysis of toluene. The results showed that the additive Ca promoted the grain refinement of metallic nickel, and interacted with Ni to form the NiO-CaO solid solution, which enhanced anti-sulfidation and anti-coking properties of catalysts and improved the reforming reaction of tar. For Ni-Ca catalysts, the highest yields of H2 and CH4 were 40.2 mL/g and 69.3 mL/g, the toluene conversion was 86.2% and the liquid yield was 35.3% at 800 ℃. In order to reduce the liquid yield and further improve the gas yield, the additive Co was supported on Ni-4 wt%Ca/HZSM-5 catalyst with the loading of 0.1–2 wt%. Ni-Co solid solution alloys with small particle size and uniform distribution were formed on the surface of HZSM-5 carrier, which made the reforming reaction move to the low temperature direction and promoted the reduction of Ni species. And during the loading process, the two additive metals, Ca and Co, were combined with each other in the form of oxides, further improving the mechanical strength and reaction stability of catalysts. The Ni-4 wt%Ca-0.1 wt%Co/HZSM-5 catalyst showed the best pyrolysis performance. The liquid recovery rate was decreased by 14.6% and the yields of H2 and CH4 were increased by 17.7% and 8.9% at 800 ℃. Most importantly, with the increase of pyrolysis temperature from 700 °C to 900 °C, the yield of pyrolysis gases and toluene conversion increased significantly. Especially, at 900 °C, the yields of H2 and CH4 produced over Ni-4 wt%Ca-0.1 wt%Co catalyst were 120.3 mL/g and 107.4 mL/g, and toluene conversion reached 98.6%. Ni-4 wt%Ca-0.1 wt%Co still maintained high catalytic activity after secondary regeneration at 900 °C.

Aluminum‑yttrium oxides supported iron for effective catalytic reforming of toluene: Promotion roles of yttrium

A facile Fe-based catalyst (FYA) was developed for tar reforming by using the Y–Al oxides as catalyst support. Toluene was used as a tar model compound to evaluate the steam reforming (TSR) activity and stability of the catalyst. By adding Y to the Fe/Al2O3 (FA), the toluene conversion efficiency was significantly improved (76% vs. 20% at 850 °C). The yttrium prevented the iron and aluminum from forming an inactive spinel phase (FeAl2O4), thus maintaining the redox activity of iron. The Fe2+/Fe3+ couple instead of metallic iron was most likely the main active phase for tar reforming. Yttrium reduced the number of surface oxygen vacancies and weakened the lattice oxygen activity to suppress the over-reduction of the iron species on FA, which maintained the composition of active FeOx for TSR. Additionally, the anti-sintering and anti-coking properties were improved significantly after Y modification causing the enhanced stability of the catalyst. The increased basic sites, especially those with medium- and high-strength, on the FYA surface are beneficial to reducing the carbon deposits (1.61 vs. 17.58 mg-C/(gcat·h)) and keeping the surface active sites exposed to the reactants during the reactions.

MOF-derived CoCeOx nanocomposite catalyst with enhanced anti-coking property for ethanol reforming with CO2

Up to date, to design the efficient catalysts for CO2 reforming with ethanol is of great challenge due to the severe coke deposition. In this work, MOF derived CoCeOx nanocomposite (CoCe-MOF) with outstanding performance for ethanol dry reforming was successfully prepared. Indeed, the experimental results revealed that ethanol conversion was 97% with a H2/CO ratio of ca.1 and negligible acetone formation (0.4 mol%) at 550 °C which was better than that of Co3O4/CeO2 synthesized by impregnation technique. Moreover, no obvious deactivation was observed even after 40 h time-on-stream tests for CoCe-MOF catalyst. Interestingly, ethanol conversion over CoCe-MOF slightly decreased from 99% to 96% while the value over Co3O4/CeO2 sample remarkably declined from 90% to 79% as well as the increase of byproduct formation (acetone from 1.1 mol% to 1.9 mol%). Particularly, the relationship between catalytic performance and morphology structure were investigated in detail by a series of characterization technique such as XRD, H2-TPR, BET, XPS, TEM, Raman etc. The results demonstrated that the uniform aliovalent incorporation of Co into CeO2 framework greatly improved the physicochemical features of the CoCe-MOF catalyst including the generation of more oxygen defects/surface oxygen species (14,5% of Ce3+ species), stronger Co-O-Ce interaction, lower temperature reducibility etc. Hence, these positive factors might explain its high activity and stability. Eventually, this study might provide a simple method to develop the high-performance catalysts for dry reforming process and other heterogeneous catalytic reactions.

Improving Anti-Coking Properties of Ni/Al2O3 Catalysts via Synergistic Effect of Metallic Nickel and Nickel Phosphides in Dry Methane Reforming

A series of NiP-x/Al2O3 catalysts containing different ratio of metallic nickel to nickel phosphides, prepared by varying Ni/P molar ratio of 4, 3, 2 through a co-impregnation method, were employed to investigate the synergistic effect of metallic nickel-nickel phosphides in dry methane reforming reaction. The Ni/Al2O3 catalyst indicates good activity along with severe carbon deposition. The presence of phosphorus increases nickel dispersion as well as the interaction between nickel and alumina support, which results in smaller nickel particles. The co-existence of metallic nickel and nickel phosphides species is confirmed at all the P contained catalysts. Due to the relative stronger CO2 dissociation ability, the NiP-x/Al2O3 catalysts indicate obvious higher resistance of carbon deposition. Furthermore, because of good balance between CH4 dissociation and CO2 dissociation, NiP-2/Al2O3 catalyst exhibits best resistance of carbon deposition, few carbon depositions were formed after 50 h of dry methane reforming.

MOF-Derived CoCeO <sub>x</sub> Nanocomposite Catalyst with Enhanced Anti-Coking Property for Ethanol Dry Reforming

MOF-Derived CoCeO <sub>x</sub> Nanocomposite Catalyst with Enhanced Anti-Coking Property for Ethanol Dry Reforming

A short review on nickel-based catalysts in dry reforming of methane: Influences of oxygen defects on anti-coking property

Abstract Nickel-based catalysts are widely used in dry reforming of methane (DRM) due to good catalytic activity and low industrial cost. However, carbon deposition hinders the large-scale applications. In this short review, the applications of perovskites, transition metal oxides, rare earth metal oxide, and mixed oxide materials in DRM are discussed based on the effects of oxygen defects. Also, the formation mechanisms of oxygen defects in nickel-based catalysts are elucidated. It is found that oxygen defects promote the movement of oxygen species and produce more surface oxygen, which effectively reduces carbon deposition in DRM.

Atomic Layer Deposition of TiO2 Thin Films on the Inner Walls of Steel Tubes Increases Anti-coking Properties.

To suppress catalytic coking, TiO2 passivation films were deposited on the inner walls of SS316 stainless steel tubes by atomic layer deposition (ALD). Indentation test results showed a platform on the indentation curve of TiO2 films grown over 2000 ALD cycles due to internal stress-induced microcracks. In coking experiments, the TiO2-coated tubes exhibited a higher heat flux and lower pressure difference than bare ones. Analysis of the coking surface revealed that TiO2 thin film passivation can reduce the size and number of particulate deposits. At the same time, passivation treatment inhibits the formation of filamentous carbon and improves anti-coking performance by reducing the ability of the tube to adsorb amorphous deposition products. The coking surfaces of TiO2-coated tubes had less graphitization, indicating that the coking products had fewer defects and lower activated carbon contents.

Coking and gas products behavior of supercritical n-decane over NiO nanoparticle/nanosheets modified HZSM-5

Endothermic hydrocarbon fuel of active thermal protection has great potential in cooling system. The bottlenecks for the practical application are the unsatisfied heat sink and severe coking issue. Here, NiO nanoparticle/nanosheet hybrid thin layers were successfully wrapped on the commercial HZSM-5 (denoted as ZSM-5@NiM), and showing significant modulation ability for the acidity properties of HZSM-5 to boost supercritical cracking of n-decane. The as-prepared catalysts make the NiO and HZSM-5 show synergistic effect which dramatically lowers the overall acidity of composite, thus changes the cracking path of n-decane, and results in effective anti-coking properties. ZSM-5@NiM decelerated many additional free radicals and generated more gases products by monomolecular beta cleavage reaction. Gases products also show positively correlating with the heat sink. The catalysts improve the heat sink of n-decane from 3.77 MJ/kg at 728 °C to 4.59 MJ/kg at 780 °C. Present work demonstrates that the introduction of nanostructured metal oxides into HZSM-5 will synergistically adjust the acidity of composite, leading to the manipulation of catalytic cracking path and extent, gas products, heat sink, coking behavior of supercritical n-decane, finally providing deep insights for the design and fabrication of catalysts for hydrocarbon fuel cracking.