Catalyst Mixture Research Articles

Unexpected Low-Temperature deNOx Activity of AdSCR Systems for Cold Start NOx Abatement

Low-temperature operation of urea selective catalytic reduction (SCR) aftertreatment systems for the abatement of NOx from diesel engines presents new challenges related to poor catalytic activity and the urea injection temperature threshold. Physical mixtures of a NH3-SCR catalyst (e.g., Fe-/Cu-zeolite) and of a NOx storage material (e.g., BaO/Al2O3, CeO2/Al2O3) have shown promising performances in terms of overall NOx removal efficiency, as they can operate both as NOx adsorbers, trapping NOx during the cold start transient, and as SCR catalysts, reducing at higher temperatures the previously stored NOx with NH3. Herein, we extend the investigation of new Cu-CHA + BaO/Al2O3 AdSCR systems (AdSCR = adsorption + selective catalytic reduction) focusing on the reactivity between NOx and ammonia in the low-temperature window (from room temperature up to 170 °C). We find that the selective reduction of NO by NH3 over Cu-CHA is surprisingly enhanced by the presence of BaO/Al2O3 when ammonia is preadsorbed, leading to the onset of nitrogen formation already at 40 °C.

Synthesis and characterization of TiO2 and palm oil fiber ash hybrid photocatalysts for seawater pretreatment

Titanium dioxide (TiO2) has been used in various applications such as air purification, water purification, and photoelectrochemical conversion systems. However, developing advanced materials with enhanced performance for catalytic applications, especially water treatment, is highly required. This work aims to study the effect of (TiO2) photocatalyst in pretreatment seawater desalination. The catalyst with a mass ratio of TiO2: palm oil fibre ash (POFA) at 0:100, 40:60, 60:40, and 100:0 was synthesized via wet impregnation. The catalyst was calcined at 500 ℃ for four hours. The mixture of artificial seawater and catalyst at a mass ratio of photocatalyst: artificial seawater at 1:300 was put in a one-litre borosilicate photo-reactor fixed with mercury light of 350 nm for two hours with stirring at 1000 rpm. In this investigation, an evaporator was used to collect the freshwater. The fresh and spent catalysts were characterized via X-Ray Diffractogram (XRD), Nitrogen physisorption analysis, Diffuse Reflectance Spectrometer (DRS), Scanning Electron Microscopy (SEM), and Energy Dispersive X-Ray Spectroscopy (EDX). The catalyst with Ti: palm oil fibre ash (POFA) at 40:60 and 60:40 can reduce the COD at 45 % and 41%, respectively. As more OPFA was added into the hybrid TiO2 catalyst, there has been a change in the properties of seawater due to the use of special evaporators, especially EC and TDS. It can be deduced that the hybrid TiO2 photocatalyst synthesized with OPFA has vast potential to treat seawater.

Effect of H-ZSM-5 and Al-MCM-41 Proportions in Catalyst Mixtures on the Composition of Bio-Oil in Ex-Situ Catalytic Pyrolysis of Lignocellulose Biomass

The present work is an attempt to optimize the proportion of H-ZSM-5 and Al-MCM-41 in the catalyst mixtures for lignocellulose biomass catalytic pyrolysis. The H-ZSM-5 proportions of 50.0, 66.7, 75.0, and 87.5 wt.% were examined for the upgrading of biomass pyrolysis vapors in the fixed bed reactor. The catalyst mixture of 87.5 wt.% H-ZSM-5 and 12.5 wt.% Al-MCM-41 was found most effective in this study, giving a 65.75% deoxygenation degree. An organic-rich bio-oil was obtained with 74.90 wt.% of carbon content, 8 wt.% of hydrogen content, 15 wt.% oxygen content, a 0.39 wt.% water content, and a high heating value of 34.15 MJ/kg. The highest amount of desirable compounds among the studied catalytic experiments, which include hydrocarbons, phenols, furans, and alcohols, was obtained with a value of 95.89%. A significant improvement in the quality of bio-oil with the utilization of H-ZSM-5 and Al-MCM-41 catalyst mixtures was the rise of desirable compounds in bio-oil.

Conversion of Dimethyl Ether to a Triptane-Enriched Mixture of Liquid Hydrocarbons: Influence of Modifier and Reaction Conditions

The influence of the active element in the alkylation catalyst as a component of a combined catalyst for the production of liquid hydrocarbons with increased triptane content from dimethyl ether was studied. A mixture of liquid hydrocarbons containing more than 8.5 wt % triptane was prepared under the optimum conditions (temperature 340°С, pressure 10 MPa, dimethyl ether weight space velocity 4 h–1) on a combined catalyst in the form of a physical mixture of catalysts (mean grain size 2–4 mm) for the synthesis of lower olefins, based on Mg-modified НZSM-5 zeolite, and for the alkylation, based on La- and Pd-modified HY zeolite.

In-situ catalytic pyrolysis upgradation of microalgae into hydrocarbon rich bio-oil: Effects of nitrogen and carbon dioxide environment

Pyrolysis of Spirulina Platensis (SP) microalgae was carried out under different reaction environment such as nitrogen (N2) and carbon dioxide (CO2) at different reaction temperatures of 300, 350, 400, 450 and 500 °C. Catalytic upgradations were examined over solid acid (ZSM-5) and solid base (MgO) catalyst, and with ZSM-5-MgO catalysts mixtures. Results showed, pyrolysis of non-catalytic biomass yielded maximum bio-oil of 43.6% under N2. However catalytic upgradation in CO2 environment produced lower bio-oil due to the coke formation. Maximum bio-oil (46.2 wt%) was obtained with basic metal MgO catalyst in N2 environment compared to other catalyst and environments. Mixture of MgO-ZSM-5 catalyst improved the bio-oil yield (37.8–48.6 wt%) compared to individual catalytic reaction under N2 and CO2. Higher high heating value (HHV) was observed in catalytic bio-oil 36.8 MJ/Kg. Bio-oil (catalytic) analysis revealed that 64–70% of compounds are in hydrocarbon range. Bio-oil was rich in hydrocarbons of C7-C18 range with less oxygenated compounds.

Eco-green biodiesel production from domestic waste cooking oil by transesterification using LiOH into basic catalysts mixtures

Eco-green biodiesel is an alternative fuel produced by a sustainable methodology and using renewable sources as feedstock due to its green nature and lower emission of pollutants in comparison with conventional fuels. In this work, biodiesels were produced using an innovative source of catalysts, a mixture of metal hydroxides: lithium-sodium (LiOH + NaOH) or lithium-potassium (LiOH + KOH) due to the considerable increase in the consumption and disposal of Li-ion battery wastes (electronic residues) in recent years. Waste cooking oil samples from fast food chains and households were used as an oily raw feedstock without any prior treatment to produce eco-green biodiesel by a transesterification reaction at room temperature. The recycling process not only removes Li-ion battery wastes and oily contaminants from the environment but also enables the generation of a green power source. The presence of lithium as a catalyst for producing eco-green biodiesel was investigated in order to verify previously the possibility of using lithium recovered from waste Li-ion batteries present in electronic devices in general. As a result, nicely followed by hydrogen nuclear magnetic resonance, the biodiesel mean yield of 90% using 5 wt. % LiOH with 95 wt. % NaOH or KOH catalysts was obtained and considered to be relatively high considering the high resolution of this technique. Gas chromatography, thin-layer chromatography, hydrogen nuclear magnetic resonance, infrared spectroscopy, density, and viscosity were the techniques performed to analyze the chemical structure and physical properties of the biodiesel (methyl esters) produced samples in the presence of a lithium catalyst.

Synthesis Gas Conversion to Lower Olefins over ZnCr‐SAPO‐34 Catalysts: Role of ZnO−ZnCr2O4 Interface

AbstractThis work reports that the ZnO−ZnCr2O4 interface was constructed by tailoring the Zn/Cr ratio and the role of ZnO−ZnCr2O4 interface in activating CO molecule for the synthesis of lower olefins over a tandem catalyst was studied. A lower olefins selectivity of 71 % at a CO conversion of 34 % was achieving on Zn1Cr1&SAPO‐34. The presence of ZnO−ZnCr2O4 interface effectively reduces the activation energy of CO hydrogenation (from 51.8 kJ/mol to 33.6 kJ/mol) and subsequently leading to the triple increase of intrinsic activity. In situ DRIFTS and XPS studies demonstrate that the better catalytic activities of Zn1Cr1 catalyst are related to the presence of ZnO−ZnCr2O4 interface, which provides more oxygen vacancy sites for CO adsorption and activation. In this sense, the Zn1Cr1 catalyst with ZnO−ZnCr2O4 interface is more active than the simple physical mixture of ZnO and Cr2O3 catalyst separately and Zn1Cr2 catalyst. This work provides fundamental insights for a rational design of Zn−Cr based catalysts and even other heterogeneous catalysts by constructing oxide‐oxide interface.

Microwave-Assisted Catalytic Fast Pyrolysis of Biomass for Hydrocarbon Production with Physically Mixed MCM-41 and ZSM-5

To delve into the law of hydrocarbon production in microwave-assisted catalytic fast pyrolysis (MACFP) of corn straw, physical mixed Mesoporous Crystalline Material-41 (MCM-41) and Zeolite Socony Mobile-5 (ZSM-5) catalyst prototypes were exploited in this study. Besides, the effects exerted by temperature of reaction and MCM-41/ZSM-5 mass ratio were explored. As revealed from the results, carbon outputs of hydrocarbons rose initially as the temperature of MACFP rose and reached the maximal data at 550 °C; subsequently, it declined as reaction temperature rose. Moreover, the MCM-41/ZSM-5 mass ratio of 1:2 was second-to-none for hydrocarbon formation in the course of biomass MACFP. It was reported that adding MCM-41 can hinder coke formation on ZSM-5. Furthermore, MCM-41/ZSM-5 mixture exhibited more significant catalytic activity than ZSM-5/MCM-41 composite, demonstrating that hydrocarbon producing process can be stimulated by a simple physical MCM-41 and ZSM-5 catalysts mixture instead of synthesizing complex hierarchically-structured ZSM-5/MCM-41 composite.

Simulated moving bed reactor for p-xylene production: Modeling, simulation, and optimization

A Simulated Moving Bed Reactor (SMBR), comprising a homogeneous mixture of adsorbent and catalyst, can overcome the equilibrium constraints in the production of p-xylene (PX). In this proposal, toluene and benzene were respectively considered as desorbent in the process. The arrangement of columns and optimum operating conditions such as switching time and flow rates that lead to maximum p-xylene productivity and minimum desorbent consumption were determined. Several constraints, including maximum pressure drop per bed and purity, were considered. Additionally, the operating temperature was optimized for the first time taking into account the energy consumption within the associated distillation columns; the heat integration involving the distillation columns was also discussed. Finally, toluene showed better performance than benzene as desorbent. For the best case studied, the optimized temperature was 540 K. Moreover, an increase of about 25% in the recovery of PX, compared to the conventional Simulated Moving Bed, was obtained.

Sorption enhanced steam reforming of methanol for high-purity hydrogen production over Cu-MgO/Al2O3 bifunctional catalysts

Sorption enhanced steam reforming of methanol (SESRM) can significantly promote the hydrogen production process with simultaneous CO2 sorption. The mechanical mixture of catalysts and sorbents as a conventional approach is complex and requires high temperatures for regeneration, which results in serious sintering of Cu-based catalysts. This paper describes a novel Cu-MgO/Al2O3 bifunctional catalysts (xCMA, x is denoted as the mass fraction of Cu, 0%–10%) via a sol–gel method for the SESRM process. We find that Cu species, including metallic Cu and Cu ions, co-exist on the catalyst. The metallic Cu on the catalyst surface is an active site for methanol steam reforming while the Cu ion in MgO lattice promotes the CO2 sorption capacity. Moreover, the incorporation of Cu ion into MgO also facilitates CO2 desorption by forming more bidentate carbonates. Due to the strong interaction between Cu and MgO, the Cu sintering is inhabited in comparison with the mechanical mixture of catalysts and sorbents. Meanwhile, MgO is found to induce more formate species to inhibit the generation of carbon monoxide. As a result, the optimal bifunctional catalyst, 8 wt% Cu-MgO/Al2O3 (8CMA) shows a superior performance in both catalytic reforming and CO2 sorption with a highest H2 selectivity of 99.3% and lowest CO selectivity (<0.15%) over 10 repeated cycles. This study suggests that the appropriate control of bifunctional catalysts can lead to powerful potential for high H2 production performance in SESRM.

Triazine-based Organic Polymer-catalysed Conversion of Epoxide to Cyclic Carbonate under Ambient CO2 Pressure.

In this work we have achieved epoxide to cyclic carbonate conversion using a metal-free polymeric catalyst under ambient CO2 pressure (1.02 atm) using a balloon setup. The triazine containing polymer (CYA-ANIS) was prepared from cyanuric chloride (CYA-Cl) and o-dianisidine (ANIS) in anhydrous DMF as solvent by refluxing under the N2 gas environment. The presence of triazine and amine functional groups in the polymer results in the adsorption of CO2 up to 7 cc/g at 273 K. This inspired us to utilize the polymer for the conversion of a series of functionalised epoxides into their corresponding cyclic carbonates in the presence of tetrabutyl ammonium iodide (TBAI) as co-catalyst. The product has wide range of applications like solvent in lithium ion battery, precursor for polycarbonate, etc. The catalyst was efficient for the conversion of different mono and di-epoxides into their corresponding cyclic carbonates under atmospheric pressure in the presence of TBAI as co-catalyst. The study indicates that epoxide attached with electron withdrawing groups (like, CH2 Cl, glycidyl ether, etc.) displayed better conversion compared to simple alkane chain attached epoxides. This is mainly due to the stabilization of electron rich intermediates produced during the reaction (e. g. epoxide ring opening or CO2 incorporation into the halo-alkoxide anion). This catalyst mixture was capable to maintain its reactivity up to five cycles without losing its activity. Post catalytic characterization clearly supports the heterogeneous and recyclable nature of the catalyst.

Pyrolysis of low-density polyethylene waste plastics using mixtures of catalysts

In the present paper, LDPE has been pyrolysed in a 1 m length semi pilot reactor at temperature range 550–650 °C for around 2 h. Commercial bentonite, kaoline, silica Gel and activated charcoal have been used as catalyst. Liquid, gas and solid fractions (residue) were quantified. Effects of pyrolysis temperature and catalysts on liquid product were investigated. It was found that using catalyst gave shorter dripping time and this dripping started at a lower temperature. PIONA analysis of liquid product has been carried out and the highest percentage of olefins was found on using bentonite as a catalyst.

Wetted Wall Photocatalytic Reactor for Methylene Blue Degradation

Titanium dioxide (TiO2) is generally known a good potential of photocatalyst to synthesis hydrogen peroxide (H2O2). The aim of this work is to generate the H2O2 via photocatalysis for further application in a sterilization system. Wetted wall photocatalytic reactor (WWPR) was particularly designed as a prototype for carrying out the experiments of photocatalytic reaction. An advantage of WWPR is a high contact surface area of feed and catalyst mixture with UV light to enhance a high efficiency to produce the H2O2. The TiO2 photocatalyst was prepared via sol-gel method and mixed with rice husk based silica dioxide (SiO2). Properties of photocatalyst were investigated by XRD, SEM and surface area and its photocatalytic performance was tested by methylene blue degradation with reaction measurement using the UV/Vis instrument. Variation of the catalysts loading and methylene blue initial concentration were studied in photocatalytic experiments. In the batch of 0. 25 g of photocatalyst with 80 mg/L methylene blue solution, the results showed that the percentage of methylene blue removal is at 89. 52% within 2 hours of reaction. This removal efficiency of methylene blue is resulted from both mechanisms of degradation by photocatalytic reaction and adsorption by the function of SiO2 modification and the trap-hole of crystallized anatase structure

Genesis of active phase in MoW/Al2O3 hydrotreating catalysts monitored by HAADF and in situ QEXAFS combined to MCR-ALS analysis

Alumina supported MoW hydrotreating catalyst was synthesized by using bimetallic H4[SiMo3W9O40] Keggin heteropolyacid (HPA). Catalysts based on monometallic H4[SiMo12O40] and H4[SiW12O40] and their mixture were also studied. Genesis of the active phase was studied during atmospheric gas sulfidation by H2S/H2 of the catalysts by in-situ Quick X-ray absorption spectroscopy (XAS) and High-Angle Annular Dark-Field (HAADF) imaging. The combination of different chemometric tools such as Principal Component Analysis (PCA) and Multivariate Curve Resolution with Alternating Least Squares (MCR-ALS) allowed to determine the number of intermediate species, their chemical nature and concentration profiles during sulfidation. It was found that tungsten sulfidation using bimetallic HPA precursor started at lower temperature, compared to W sulfidation in the monometallic and in the mixture of monometallic HPA catalysts. Simultaneous sulfidation of Mo and W atoms in case of the bimetallic molecular precursor can govern the formation of mixed MoWS2 phase, which formation during activation was evidenced by HAADF.

Metal–Organic Layers for Synergistic Lewis Acid and Photoredox Catalysis

We report the design of a new multifunctional metal-organic layer (MOL), Hf12-Ir-OTf, comprising triflate (OTf)-capped Hf12 secondary building units (SBUs) and photosensitizing Ir(DBB)[dF(CF3)ppy]2+ [DBB-Ir-F, DBB = 4,4'-di(4-benzoato)-2,2'-bipyridine; dF(CF3)ppy = 2-(2,4-difluorophenyl)-5-(trifluoromethyl)pyridine] bridging ligands. Hf12-Ir-OTf effectively catalyzed dehydrogenative cross-couplings of heteroarenes with ethers, amines, and unactivated alkanes with turnover numbers of 930, 790, and 950, respectively. Hf12-Ir-OTf also competently catalyzed late-stage functionalization of bioactive and drug molecules such as caffeine, Fasudil, and Metyrapone. The superior catalytic performance of Hf12-Ir-OTf over a mixture of photoredox catalyst and stoichiometric amounts of Brønsted acids or substoichiometric amounts (20 mol %) of Lewis acids is attributed to the close proximity (1.2 nm) between photoredox and Lewis acid catalysts in Hf12-Ir-OTf, which not only facilitates the reaction between the carbon radical and the activated heteroarene but also accelerates the electron transfer from the nitrogen radical intermediate to the Ir(IV) species in the catalytic cycle.

Development of a Tethered Palladium–BODIPY Dual Catalyst for Enhanced Photo- and Thermally Activated Catalysis, and for Promoting Sequential Reactivity

In recent years there has been a growing interest in merging different types of catalysis to create new multistep catalytic processes. However, the majority of reported dual catalysis strategies use a mixture of individual catalysts, with limited reports of dual catalysis reactions where the different catalysts are combined in a single compound. This work reports the synthesis of a tethered palladium-BODIPY dual catalyst to enable increased synergistic interactions between the catalytic centres. Detailed analysis, including single crystal X-ray crystallography, absorption, fluorescence, and phosphorescence measurements, and kinetic analyses to determine singlet oxygen quantum yields, confirm that chemical tethering results in a significant increase in the photocatalytic potential of the palladium-BODIPY dual catalyst, relative to the parent BODIPY chromophore. Interestingly, the palladium-BODIPY complex also exhibited rare long-lived room temperature phosphorescence. Catalytic applications of the palladium-BODIPY dual catalyst indicate that chemical tethering increases the reactivity of the catalytic centres for both photocatalytic oxidation of thioanisole and palladium catalysed Suzuki–Miyaura cross coupling, highlighting that enhancements in both photo and thermally activated catalysis can be achieved on chemical tethering. In addition, the dual catalytic potential of the palladium-BODIPY catalyst was demonstrated using a representative sequential photocatalytic oxidation–cross coupling reaction.

Tungsten–zirconia-supported rhenium catalyst combined with a deoxydehydration catalyst for the one-pot synthesis of 1,4-butanediol from 1,4-anhydroerythritol

Biomass-derived 1,4-anhydroerythritol is reduced to 1,4-butanediol over a reusable mixture of heterogeneous catalysts, ReOx–Au/CeO2 and ReOx/WO3–ZrO2.

Using modeling to select catalyst dilution methods for mass transfer intensification in lab gas–liquid fixed-bed reactors

Heterogeneous catalyst testing methodology at the lab scale must provide intrinsic kinetics data for reactor design purposes as well as the intrinsic activity ranking during catalyst screening in the field of refining and petrochemistry. The significant downscaling of the past century coupled with the increasingly active catalytic formulations may introduce considerable momentum, mass and heat effects in experiments at small scale. Catalyst dilution has emerged as one versatile and robust way to reduce the impact of momentum and heat effects on heterogeneous catalyst testing. This paper presents a methodology based on global phenomena and catalyst dilution modeling to assess and optimize reactor loading techniques for specific problems. More particularly, the aim is to provide catalysts developers and kinetics experts with concrete guidelines for intensifying gas-liquid mass transfer in lab gas–liquid fixed-bed reactors through catalyst dilution. The methodology is applied to the kinetics determination of the oil residue Hydrodemetallation (HDM) and to the screening of catalysts for benzene hydrogenation. Layered dilution, consisting on the split of the catalyst in two beds separated by an intermediate bed containing an inert material of the same size as the catalyst, poorly improves gas–liquid mass transfer. Uniform dilution, based on the direct mixture of catalyst and inert material of the same size, significantly enhances gas–liquid mass transfer as the reactant local consumption per reactor unit volume is strongly reduced. Combinations of both abovementioned dilution techniques can be used with fast and/or high stoichiometric factor chemical systems operated at conversions higher than 70%. A new criterion is proposed to calculate the minimum dilution factor to guarantee negligible gas–liquid mass transfer limitations as a function of conversion, external mass transfer and global pseudo second-order kinetics.

Pyrolysis of polystyrene plastic waste using bentonite catalyst

Polystyrene is one type of plastic that is widely used in industrially and daily life. Polystyrene properties are difficult to be degraded by nature. Hence it produces a problem for the environment. Pyrolysis of polystyrene waste is one of methods for plastic recycling. Pyrolysis polystyrene in a batch reactor for the recovery of styrene monomers (C8H8). This study aims to investigate the effect of bentonite in catalytic pyrolysis of polystyrene waste. Pyrolysis was carried out at a temperature of 300-550°C in a batch reactor with a mixture of polystyrene waste and catalyst of 0%, 5%, 10%, 15%, 20%, and 25% of polystyrene. The liquid product was analyzed using GC-MS to determine the components. The maximum yield of liquid product was obtained at 88.78% (wt%), using 25% of catalyst. The result of liquid analysis by GC-MS contains styrene compounds (C8H8), Toluene, Benzene, were the major components. Pyrolysis with a catalyst weight of 25% and temperature of 400°C obtained the maximum yield of styrene compounds (C8H8) at 32.34%.

Green and selective toluene oxidation–Knoevenagel-condensation domino reaction over Ce- and Bi-based CeBi mixed oxide mixtures

Both Bi- and Ce-based CeBi mixed oxides were prepared by a modified sol-gel process from their precursor salts. The mixed as well as the parent oxides were characterized by X-ray diffractometry, Raman, XPS, UV–DRS and X-ray photoelectron spectroscopies, ICP–OES method, scanning and transmission electron microscopies as well as BET surface area, CO2- and NH3-temperature-programmed desorption measurements. After characterizing the morphology, the acid-base properties, the oxidation states of the cationic components and the porosity of these structures, their catalytic activities were probed in the Koevenagel condensation of benzaldehyde and diethyl malonate and the toluene oxidation to benzaldehyde reactions. Based on the catalytic activities of the oxides in the individual reactions, a catalyst mixture from the Bi- and Ce-based mixed oxides was used successfully in the toluene to benzaldehyde oxidation and benzaldehyde to benzylidene malonate Knoevenagel condensation domino reaction under environmentally benign conditions.