Cause Of Deactivation Research Articles

Regeneration of methane splitting catalysts by interfacial hydrogenation

Methane splitting, also known as decomposition or pyrolysis, has a unique potential to accelerate the transition from the current carbon-based economy towards the foreseen hydrogen economy. Low-temperature catalytic methane splitting systems are unavailable due to fast catalyst deactivation, caused by solid carbon that encapsulates the catalyst. Catalyst regeneration must be performed to reactivate the catalyst and achieve a long-term operational lifetime. This can be accomplished by cyclically refeeding a portion of the produced hydrogen back to the catalyst, which promotes the hydrogenation of carbon atoms, preferentially at the interface between carbon deposits and catalytic nanoparticles. Interfacial hydrogenation ideally breaks the bonds that connect carbon allotrope products to the metal catalyst, causing the former to detach, and freeing the catalytic metal surface for further reaction. In this work, a proof-of-concept of this technology is provided, showing the full regeneration of a bulk-type Ni catalyst during 22 cycles of methane splitting, at 550 °C and 1 bar. Furthermore, a commercial SiO2-Al2O3-supported Ni catalyst has been used to study the regenerability of a highly active nanostructured material by interfacial hydrogenation, using different reactor designs. It has been demonstrated that regeneration is beneficial to improve the stability of Ni-based systems, at the applied working conditions. Nevertheless, tip-grown carbon nanotubes were considered as a cause of permanent deactivation, which could not be solved by refeeding hydrogen into the system.

Deactivation effect of elemental mercury oxidation over a V2O5-WO3/TiO2 catalyst by Pb in simulated coal-fired flue gas

Lead (Pb) is a typical heavy metal in the flue gas of coal-fired power plants, which can cause the deactivation of SCR catalysts. In this study, Pb-doped vanadium-based catalysts were prepared and investigated for the deactivation effect and mechanism of elemental Hg oxidation caused by Pb. The results showed that doping Pb on vanadium-based catalysts led to severe deactivation, which was more pronounced with increased Pb content. Further investigation illustrated that the introduction of Pb not only weakened the BET surface properties of vanadium-based catalysts but also increased the aggregation of surface species on the catalysts. After Pb introduction, the adsorption capacity toward elemental Hg, proportion of highly oxidized V5+, and surface Oβ ratio significantly decreased severely weakening the activity of the catalyst. In addition, we demonstrated that the reaction between Pb and active VO/V−OH groups of the catalyst formed inactive V−O−Pb species, which was the direct cause of catalyst deactivation.

Methanol Steam Reforming for Hydrogen Production over Ni-Based Catalysts: State-Of-The-Art Review and Future Prospects.

With increasing global emphasis on environmental sustainability, the reliance on traditional energy sources such as coal, natural gas, and oil are encountering significant challenges. H2, known for its high energy content and pollution-free usage, emerges as a promising alternative. However, despite the great potential of H2, approximately 95 % of hydrogen production still depends on non-renewable resources. Hence, the shift towards producing H2 from renewable sources, particularly through methods like steam reforming of methanol - a renewable resource - represents a beacon of hope for advancing sustainable energy practices. This review comprehensively examines recent advancements in efficient H2 production using Ni-based catalysts in methanol steam reforming (MSR) and proposes the future prospects. Firstly, the fundamental principles of MSR technology and the significance in clean energy generation are elucidated. Subsequently, the design, synthesis techniques, and optimization strategies for enhancing the catalytic performance of Ni-based catalysts are discussed. Through the analysis of various catalyst compositions, structural adjustments, surface active sites, and modification methods, the review uncovers effective approaches for boosting the activity and durability of MSR reactions. Moreover, the review investigates the causes of deactivation in Ni-based catalysts during MSR reactions and proposes strategies for extending catalyst lifespan through fine design and optimization of operation parameters. Lastly, this review outlines the current research challenges and anticipates the future trends and potential applications of Ni-based catalysts in MSR hydrogen production. By offering a comprehensive critical analysis, this review serves as a valuable reference to enhance MSR hydrogen production efficiency and catalyst performance.

Feasibility of sustainable reusability of Ni/char catalyst for synthetic gas production via catalytic steam gasification

Ni/char catalyst is one of the most promising catalysts for enhancing gas production, particularly syngas from catalytic steam gasification of biomass. In the current study, one unmodified (Ni/MMchar) and two modified catalysts (Ni/NaMMchar and Ni/NaAceMMchar) were utilized to investigate the reusability potential of Ni/char catalyst for catalytic steam gasification of bamboo in a two-stage fixed-bed reactor including the changes in catalyst characteristics. N2 adsorption-desorption by BET, scanning electron microscope connected with energy-dispersive X-ray spectrometer (SEM-EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses were utilized for examining their characteristics. The findings indicated that the three catalysts could maintain the reusability potential in catalytic steam gasification of bamboo for twice cycles. The syngas reduction percentages in the second cycles of the catalysts ranged between 11.0 and 22.8 %. H2/CO ratios of all spent catalysts lined in the range of 4.10 − 2.45. The low heating values of syngas products were in the range of 8.83–8.19 MJ/Nm3. Considering the catalyst characteristics, the increasing cycles of catalyst operations induced carbon deposition, resulting in the reduction of specific surface areas. SEM-EDS images of the used catalysts appeared the coke layer and the Ni metal sintering on the surfaces. The uses of catalysts encouraged the transformation of Ni metal active site into NiO, Ni2O3 and Ni3C forms. These phenomena were the major causes of catalyst deactivation. The changes in the characteristics and catalyst activity controlled the gasification reactions, resulting in the catalyst deactivation and gaseous products.

Promoting propane dehydrogenation performance of Co/silicalite-1 catalysts

Co catalysts supported on silicalite-1 (S-1) zeolite are developed in this work for direct propane dehydrogenation to propylene (PDH), showing excellent activity and propylene selectivity. Comprehensive characterizations of XRD, SEM, N2-sorption, TEM, DR UV–vis, H2-TPR, and TGA jointly evidence that the atomic-level dispersed CoOx species have significantly positive influence on the catalytic performance for PDH reaction. Alkaline treatment is a kind of advanced and effective method to create a number of defects on S-1 support, further isolating CoOx species and thus depressing side reactions. After the optimizing treatment on support, the catalyst with 0.5 wt% of Co supported on the S-1 pretreated with 0.1 mol/L of NaOH solution can exhibit simultaneously 78 % of propane conversion and 97 % of propylene selectivity after 15-minute of induction period. This work confirms that the highly-dispersed CoOx species bonded to zeolite are necessary for obtaining highly active and selective Co sites confined in the developed oxygen defects for the PDH reaction possibly due to the interface-induced effect between Co-O, and the main deactivation cause is ascribed to the migration and aggregation of Co sites in defects which points out that the direction for developing commercial Co based catalysts should focus on the stability design of active single Co atoms.

Gas-phase surface modification to control catalyst structure and yields in methane dehydroaromatization

Methane dehydroaromatization (MDA) is a promising approach for direct methane transformation to aromatics and hydrogen. The benchmark catalyst Mo/H-ZSM-5 struggles to find commercial adoption because of thermodynamically-limited yields and rapid coking on Brønsted acid and molybdenum carbide species, especially on zeolite external surfaces. Here, gas-phase atomic layer deposition (ALD) overcoats H-ZSM-5 external surfaces with SiO2 or Al2O3. NH3-TPD, HRTEM, and textural properties show that these overcoats exclusively passivate zeolite external surfaces. Under MDA conditions, SiO2 gives softer coke and increases cumulative benzene yields by 25 %, while Al2O3 strongly decreases yields. H2-TPR and UV–visible and Raman spectroscopy show how the overcoats redisperse the MoOx precatalysts, especially over multiple deactivation and isothermal oxidative regeneration cycles. Combined with 27Al-MAS NMR, MoOx redistribution and dealumination are seen as the causes of long-term deactivation over multiple regeneration cycles, and this process continues to occur regardless of the overcoat. Overall, the deposition of a small amount of silica on the outer surface of Mo/H-ZSM-5 reduces the formation of hard coke, which could be regenerated by milder methods such as hydrogen treatment.

Decarbonized core-shell-like structure: Enhancing Fe-based oxygen carriers for superior hydrogen selectivity and stability

Fe-based oxygen carriers undergo deactivation due to repeated oxidation-reduction cycles in chemical looping gasification. The primary cause of deactivation lies in the agglomeration and phase separation behavior exhibited by Fe-based oxygen carriers. In this research, a core-shell-like structure was developed to strengthen the structural stability of the oxygen carrier. This was achieved by constraining the thermal motion dimensions of active sites and establishing two pathways for oxygen ion transport. Briefly, the core-shell-like structure was constructed with NiFe2O4 as the core and CaO as the shell. Through characterization analysis, it was found that the interaction between the core-shell-like structures resulted in lattice distortion, promoting the generation of oxygen vacancies and providing a prerequisite foundation for the rapid reaction of lattice oxygen. Furthermore, the protective mechanism of the core-shell-like structure on the active sites inhibited the agglomeration behavior of the oxygen carrier. Remarkably, a hydrogen yield of 70 % was achieved at a temperature of 600 °C, and the reaction characteristics remained stable over 20 cycles of experimentation. Density functional theory calculations revealed that C atoms present stronger electron transfer at the core-shell-like structure, which induces stronger adsorption energy.

Catalytic Esterification of Pentaerythritol over a Mesoporous Composite SnCl2@HZSM‐5 Catalyst

AbstractThe mesoporous HZSM‐5 and SnCl2@HZSM‐5 mesoporous composite were prepared by two‐step crystallization and wet impregnation method, respectively. The catalytic esterification performances of SnCl2, HZSM‐5 and SnCl2@HZSM‐5 were compared. SnCl2@HZSM‐5 had the most amount of total and weak acidity, and the weakest acid strength. More total acid content was beneficial to increase pentaerythritol conversion, and the weak acid could improve the selectivity of PETS, and weak acid strength was beneficial to inhibit the formation of carbon deposits. Brönsted and Lewis acid sites were present simultaneously on the SnCl2@HZSM‐5 catalyst. Moreover, some extra Brönsted acid sites were created on the SnCl2@HZSM‐5 catalyst, because the interaction of SnCl2 with HZSM‐5 may result in the exchange of Sn2+ with protons. Both acid sites could catalyze the esterification reaction, and the Brönsted acid site was more beneficial to increasing PETS selectivity. Therefore, SnCl2@HZSM‐5 showed the highest pentaerythritol conversion, PETS selectivity and catalytic stability. The generation of coke and the leaching of Sn were the main cause of catalyst deactivation. Under the optimized process conditions: 105 °C, 4.7 molar ratio of stearic acid and pentaerythritol, 1.2 wt % catalyst amount and 2.5 wt % SnCl2 loading, after 3 h reaction time, the pentaerythritol conversion, PETS selectivity and yield was 99.3 %, 97.2 % and 96.5 %, respectively.

Study on the mechanism of carbon nanotube-like carbon deposition in tar catalytic reforming over Ni-based catalysts

The use of Ni-based catalysts is a common method for eliminating tar through catalytic cracking. Carbon deposition is the main cause of deactivation in Ni/ZSM-5 catalysts, with filamentous MWCNTs being the primary form of carbon deposits. This study investigates the formation and evolution of CNTs during the catalytic process of biomass tar to explore the mechanism behind carbon deposition. The effect of the 9Ni/10MWCNTs/81ZSM-5 on toluene reforming was investigated through a vertical furnace. Gases produced by tar catalysis were evaluated through GC analysis. The physicochemical structure, properties and catalytic performance of the catalyst were also tested. TG analysis was used to assess the accumulation and oxidation reactivity of carbon on the catalyst surface. An analysis was conducted on the mechanism of carbon deposition during catalyst deactivation in tar catalysis. The results showed that the 9Ni/91ZSM-5 had a superior toluene conversion of 60.49%, but also experienced rapid and substantial carbon deposition up to 52.69%. Carbon is mainly deposited as curved filaments on both the surface and pore channels of the catalyst. In some cases, tip growth occurs where both carbon deposition and Ni coexist. Furthermore, specific surface area and micropore volume are reduced to varying degrees due to carbon deposition. With the time increased, the amount of carbon deposited on the catalyst surface increased to 62.81%, which gradually approached saturation, and the overall performance of the catalyst was stabilized. This situation causes toluene molecules to detach from the active sites within the catalyst, hindering gas release, which leads to reduced catalytic activity and further carbon deposition. It provides both a basis for the development of new catalysts and an economically feasible solution for practical tar reduction and removal.

Coke formation on different metal-modified (Co, Mo and Zr) ZSM-5 in the catalytic pyrolysis of cellulose to light aromatics

Catalytic pyrolysis of biomass is regarded as a promising method for preparing value-added products. However, the main factors limiting the development of the process at present are the low yield of value-added products and poor selectivity, especially for rapid catalyst deactivation due to coke deposition. The present study focuses on the catalytic pyrolysis of cellulose over metal Co-, Mo-, and Zr-loaded catalysts using a falling fixed bed at 600 °C to evaluate the type of coking of the catalysts as well as the effect of the different metal active sites on the formation of coke deposits. The introduction of Co and Mo metal sites increased the light aromatics yield of ZSM-5 from 128.9 mg/g to 147.2 mg/g and 143.0 mg/g. And the yield of coke deposits decreased from 8.3 to 6.8 and 5.1 wt%. The stability evaluation of the catalyst showed that the deactivation degree of ZSM-5 of the supported metal Co was lower than that of commercial ZSM-5, while the ZSM-5 of the supported metal Mo was rapidly deactivated. The deactivation of the catalysts depended more on the morphology or location of the accumulated coke than on the total amount deposited. The clogging of metal and acidic sites on the surface of the zeolite and the pore channels by the amorphous encapsulating coke was the main cause of catalyst deactivation. The metal Mo active sites promoted dehydrogenation coupling and hydrogen transfer during coke formation, forming a more highly disordered multiring structure, and the metal Co active sites were more capable of decomposing macromolecular compounds, olefins and alkanes, and promoted the formation of graphite-like structural carbon.

Hydrogenolysis of Glycerol over NiCeZr Catalyst Modified with Mg, Cu, and Sn at the Surface Level.

Biomass valorization is an essential strategy for converting organic resources into valuable energy and chemicals, contributing to the circular economy, and reducing carbon footprints. Glycerol, a byproduct of biodiesel production, can be used as a feedstock for a variety of high-value products and can contribute to reducing the carbon footprint. This study examines the impact of surface-level modifications of Mg, Cu, and Sn on Ni-Ce-Zr catalysts for the hydrogenolysis of glycerol, with in situ generated hydrogen. The aim of this approach is to enhance the efficiency and sustainability of the biomass valorization process. However, the surface modification resulted in a decrease in the global conversion of glycerol due to the reduced availability of metal sites. The study found that valuable products, such as H2 and CH4 in the gas phase, and 1,2-PG in the liquid phase, were obtained. The majority of the liquid fraction was observed, particularly for Cu- and Sn-doped catalysts, which was attributed to their increased acidity. The primary selectivity was towards the cleavage of the C-O bond. Post-reaction characterizations revealed that the primary causes of deactivation was leaching, which was reduced by the inclusion of Cu and Sn. These findings demonstrate the potential of Cu- and Sn-modified Ni-Ce-Zr catalysts to provide a sustainable pathway for converting glycerol into value-added chemicals.

Insight studies on the deactivation of sulfuric acid regeneration catalyst

The SAR unit is used for regenerating spent sulfuric acid for alkylation reactions. In the SAR unit, the converter employs a potassium and vanadium-based catalyst for conversion of SO2 to SO3. The multiple bed fixed bed reactor is there to ensure that almost entire amount of SO2 is converted to SO3. On observing the generation of large amounts of fines in the reactor catalyst, the spent catalyst and fines are collected for insight studies. The current study enlightens the possible causes of catalyst deactivation and fines generation. Structural changes in potassium/vanadium based catalyst during the oxidation of sulfur dioxide identified as the major cause of catalyst deactivation. Such structural changes and their impact on catalyst property were determined using various physico-chemical characterization methods like crushing strength, Loss on drying (LOD), XRF, XRD, FTIR and XPS analysis. LOD analysis shows the higher moisture and volatile content in spent and fines compared to fresh catalyst. High moisture content in spent catalyst decreases hardness of catalyst resulting in leaching of vanadium salt and carrier degradation due to thermal cycling. Chemical analysis data found to show the active vanadium content in fines is higher compared to spent which indicates vanadium has leached out from fresh catalyst and is deposited on fines. These observations are further correlated with XRD and XPS results. XPS analysis shows the relative distribution of V4+ and V5+ species on the catalyst surface are altered and found very low concentration of V4+ sites on spent catalyst. The XRD analysis demonstrates the leaching of the active component, potassium vanadyl sulfate K(VO2) (SO4)·3H2O, which then accumulated in the fines fraction. FT-IR and XRD results further shows increase in sulfate accumulation on spent catalyst surface along with phase changes. FTIR analysis of simulated spent catalyst are well correlated with these findings.

Understanding the catalytic performance and deactivation behaviour of second-promoter doped Pt/WOx/γ-Al2O3 catalysts in the glycerol hydrogenolysis for selective and cleaner production of 1,3-propanediol

The selective aqueous-phase glycerol hydrogenolysis is a promising reaction to produce commercially useful 1,3-propanediol (1,3-PDO). The Pt-WOx bifunctional catalyst can catalyse the glycerol hydrogenolysis but the catalyst deactivation via sintering, metal leaching, and coking can predominantly occur in the aqueous phase reaction. In this work, the effect of reaction temperature, pressure and second promoter (Cu, Fe, Rh, Mn, Re, Ru, Ir, Sn, B, and P) on catalytic performance and deactivation behaviour of Pt/WOx/γ-Al2O3 was investigated. When doped with Rh, Mn, Re, Ru, Ir, B, and P, the second promoter boosts catalytic activity by promoting great dispersion of Pt on support and increasing Pt surface area. The increased Brønsted acid sites lead to selective synthesis of 1,3-PDO than 1,2-propanediol (1,2-PDO). The characterization studies of fresh and spent catalysts reveal that the main cause of catalyst deactivation is the Pt sintering, as interpreted based on XRD, CO chemisorption, and TEM analyses. The Pt sintering is affected depending on the second promoter that can either or reduce the interaction between Pt, WOx, and Al2O3. As an electron acceptor of Pt in Pt/WOx/γ-Al2O3, Re and Mn as second promoters resulted in increased Pt2+ on the catalytic surface, which strengthens the contact between Pt and γ-Al2O3 and WOx, resulting in a decrease in Pt sintering. The metal leaching and coking are not affected by the presence of second promoter. The catalyst modified with a second promoter possesses improved catalytic activity and 1,3-PDO production, however the stability continues to remain a challenge. The present work unravelled the determining parameters of catalytic activity and deactivation, thus providing a promising protocol toward effective catalysts for glycerol hydrogenolysis.

Exploring Deactivation Reasons of Biomass-Based Phosphorus-Doped Carbon as a Metal-Free Catalyst in the Catalytic Dehydroaromatization of n-Heptane.

Catalytic dehydroaromatization of n-alkanes into high-value aromatics has garnered extensive interest from both academia and industry. Our group has previously reported that phosphorus-doped carbon materials exhibit high selectivity for C-H bond activation in the dehydroaromatization of n-hexane. In this study, using n-heptane as a probe, we synthesized biomass-based phosphorus-doped carbon catalysts to investigate the impact of hydrogen heat treatment and carbon deposition on catalyst structure. Despite achieving an initial conversion of n-heptane at approximately 99.6%, with a toluene selectivity of 87.9%, the catalyst activity fell quickly. Moreover, longer hydrogen treatment time and higher hydrogen concentrations were found to accelerate catalyst deactivation. Thermogravimetric analysis (TGA) and N2 adsorption measurements (BET) indicated that a small amount of coke deposition was not the primary cause of catalyst deactivation. Temperature-programmed desorption of ammonia gas (NH3-TPD) revealed a significant decrease in acid-active functional groups. X-ray photoelectron spectroscopy (XPS) and solid-state 31P NMR spectroscopy confirmed the reduction of active central phosphorus species. These results suggest that catalyst deactivation primarily arises from the decrease in acidity and the partial reduction of phosphorus-containing groups, leading to a substantial loss of active sites. This work contributes new perspectives to understanding the properties and design improvements of metal-free carbon catalysts.

Structure characterization of aged automobile exhaust catalysts using electron probe microanalysis

BackgroundDriven by emission regulations, the technology of emission control catalysts has been under increasing need for development. Understanding the deactivation mechanism of aged or spent automobile exhaust catalysts is the key to extending their service lifetime. However, the lack of comprehensive microstructural characterization results in an incomplete understanding of their physicochemical properties. Deactivation mechanism of automobile exhaust catalysts is a considerably complex phenomenon, it can be classified into three groups based on its origin: thermal sintering, chemical poisoning and mechanical deactivation. ResultsIn this study, an aged high-mileage automobile exhaust catalyst with Pd and Rh active phases supported on a cerium zirconium oxide doped alumina coating on cordierite was analysed; six consecutive monolithic blocks along the inlet to the outlet of the aged catalyst were extracted, and the corresponding metallographic samples were fabricated using the vacuum impregnation resin method. The purpose of this study was to accurately characterize the different regions of the monolith via electron probe microanalysis and to infer potential causes of catalyst deactivation. Two major causes of deactivation were found: (1) aggregation and alloying of precious-metal particles caused by thermal sintering and (2) chemical poisoning caused by sulphur and phosphorus. Other mechanisms, such as mechanical degradation, which mainly manifests as the loss or wear of the washed coating, were also found to be involved in deactivation. Additionally, the catalytic activity tests showed a considerable decrease in the aged catalyst. The poison concentration trends in the washcoat indicated that P is detrimental to CO oxidation, while S accumulation affects propane oxidation. SignificanceThis analysis method can be of substantial practical significance in developing advanced washcoat materials. Meanwhile, it has great potential in the washcoat analysis of honeycomb-shaped monolithic catalyst, such as natural gas catalyst, diesel vehicle oxidation catalyst and other honeycomb catalysts applied in chemical industry.

Controlling Pt nanoparticle sintering by sub-monolayer MgO ALD thin films.

Metal nanoparticle (NP) sintering is a major cause of catalyst deactivation, as NP growth reduces the surface area available for reaction. A promising route to halt sintering is to deposit a protective overcoat on the catalyst surface, followed by annealing to generate overlayer porosity for gas transport to the NPs. Yet, such a combined deposition-annealing approach lacks structural control over the cracked protection layer and the number of NP surface atoms available for reaction. Herein, we exploit the tailoring capabilities of atomic layer deposition (ALD) to deposit MgO overcoats on archetypal Pt NP catalysts with thicknesses ranging from sub-monolayers to nm-range thin films. Two different ALD processes are studied for the growth of MgO overcoats on Pt NPs anchored on a SiO2 support, using Mg(EtCp)2 and H2O, and Mg(TMHD)2 and O3, respectively. Spectroscopic ellipsometry and X-ray photoelectron spectroscopy measurements reveal significant growth on both SiO2 and Pt for the former process, while the latter exhibits a drastically lower growth per cycle with an initial chemical selectivity towards Pt. These differences in MgO growth characteristics have implications for the availability of uncoated Pt surface atoms at different stages of the ALD process, as probed by low energy ion scattering, and for the sintering behavior during O2 annealing, as monitored in situ with grazing incidence small angle X-ray scattering (in situ GISAXS). The Mg(TMHD)2-O3 ALD process enables exquisite coverage control allowing a balance between physically blocking the Pt surface to prevent sintering and keeping Pt surface atoms free for reaction. This approach avoids the need for post-annealing, hence also safeguarding the structural integrity of the as-deposited overcoat.

Nanoscale Chemical Diversity of Coke Deposits on Nanoprinted Metal Catalysts Visualized by Tip-Enhanced Raman Spectroscopy.

Coke formation is the prime cause of catalyst deactivation, where undesired carbon wastes block the catalyst surface and hinder further reaction in a broad gamut of industrial chemical processes. Yet, the origins of coke formation and their distribution across the catalyst remain elusive, obstructing the design of coke-resistant catalysts. Here, the first-time application of tip-enhanced Raman spectroscopy (TERS) is demonstrated as a nanoscale chemical probe to localize and identify coke deposits on a post-mortem metal nanocatalyst. Monitoring coke at the nanoscale circumvents bulk averaging and reveals the local nature of coke with unmatched detail. The nature of coke is chemically diverse and ranges from nanocrystalline graphite to disordered and polymeric coke, even on a single nanoscale location of a top-down nanoprinted SiO2 -supported Pt catalyst. Surprisingly, not all Pt is an equal producer of coke, where clear isolated coke "hotspots" are present non-homogeneously on Pt which generate large amounts of disordered coke. After their formation, coke shifts to the support and undergoes long-range transport on the surrounding SiO2 surface, where it becomes more graphitic. The presented results provide novel guidelines to selectively free-up the coked metal surface at more mild rejuvenation conditions, thus securing the long-term catalyst stability.

Characterization of Equilibrium Catalysts from the Fluid Catalytic Cracking Process of Atmospheric Residue

In the FCC conversion of heavy petroleum fractions as atmospheric residues, the main challenge for refiners to achieve the quantity and quality of various commercial products depends essentially on the catalyst used in the process. A deep characterization of the catalyst at different steps of the process (fresh, regenerated, and spent catalyst) was investigated to study the catalyst’s behavior including the physicochemical evolution, the deactivation factor, and kinetic–thermodynamic parameters. All samples were characterized using various spectroscopy methods such as N2 adsorption–desorption, UV-visible spectroscopy, Raman spectroscopy, LECO carbon analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF), nuclear magnetic resonance spectroscopy (NMR13C) analysis, and thermogravimetric analysis. The results of the N2 adsorption–desorption, UV-vis, Raman, LECO carbon, and SEM imaging showed that the main causes of catalyst deactivation and coking were the deposition of carbon species that covered the active sites and clogged the pores, and the attrition factor due to thermal conditions and poisonous metals. The XRD and XRF results showed the catalyst’s physicochemical evolution during the process and the different interlinks between catalyst and feedstock (Nickel, Vanadium, Sulfur, and Iron) elements which should be responsible for the coking and catalyst attrition factor. It has been found that, in addition to the temperature, the residence time of the catalyst in the process also influences catalyst structure transformation. NMR13C analysis revealed that polyaromatic hydrocarbon is the main component in the deposited coke of the spent catalyst. The pyridine-FTIR indicates that the catalyst thermal treatment has an influence on its Brønsted and Lewis acid sites and the distribution of the products. Thermogravimetric analysis showed that the order of catalyst mass loss was fresh > regenerated > spent catalyst due to the progressive losses of the hydroxyl bonds (OH) and the structure change along the catalyst thermal treatment. Moreover, the kinetic and thermodynamic parameters showed that all zones are non-spontaneous endothermic reactions.

Effect of oxygen on produced hydrocarbons and hydrogen from CO2 reduction photocatalytic process

A possible approach to addressing the challenges of energy scarcity and the effects of global warming through the decrease of greenhouse gases is the manufacture of hydrocarbons, particularly fuel from the photoreduction of CO2. Here, the determination of activity/selectivity of produced hydrocarbons, hydrogen, and oxygen in the gas phase was demonstrated in the absence and presence of O2 in an aqueous slurry on TiO2. The conversion increases with reaction time up to the first hour but then begins to become unchanged in the presence of oxygen, suggesting catalyst deactivation. In contrast, the reaction rate and CO2 conversion increased over 4 h when there was no oxygen, demonstrating that oxygen can be the cause of TiO2 deactivation. Intriguingly, light-induced O2 uptake rather than evolution was seen during optical oxygen detection investigations in photoreactions with a peak region of O2/CO2. H2 production is suppressed by the presence of oxygen. Additionally, the sudden increase in hydrogen generation when oxygen is absent demonstrated that oxygen consumption and hydrogen production are taking place at the reduction site. The availability of oxygen reduced hydrocarbon productivity and H2 production.

NiCu-based catalysts for the low-temperature hydrodeoxygenation of anisole: Effect of the metal ratio on SiO2 and γ-Al2O3 supports

The effects of the metal ratio of NiCu catalysts on the low-temperature hydrodeoxygenation (HDO) of anisole were assessed on a neutral SiO2 and an acidic γ-Al2O3 support. The activity of SiO2-supported catalysts increases with the Ni content in the NiCu phase, related to Ni’s hydrogenation capacity. In contrast, on a γ-Al2O3 support, the activity decreases with the Ni content. Overall, Al2O3-supported catalysts, exhibiting a smaller NiCu alloy particle size, are more active than SiO2-supported ones. In terms of selectivity, SiO2-supported catalysts mainly hydrogenate anisole to methoxycyclohexane, while, particularly at higher conversions, γ-Al2O3-supported catalysts are able to further convert methoxycyclohexane to cyclohexane, demonstrating the importance of acid sites for low-temperature HDO. The Ni/Cu ratio also steers the selectivity, but not the catalyst stability. Deactivation phenomena are only support dependent: while on SiO2-supported catalysts, active site sintering occurs, attributed to weak stabilization of metal particles by the support, acid catalyzed coking is the main cause of deactivation on the γ-Al2O3-supported catalysts.