Ammonia TPD Research Articles

Hydroprocessing of Gasoline on Modified Alumina Catalysts

The hydroprocessing of gasoline on modified alumina catalysts makes it possible to obtain high-octane products. The implementation and development of the process have largely become possible due to the development of modified alumina catalysts that do not contain noble metals and exhibit special catalytic properties. This article discusses topical issues of petrochemistry, namely the creation of catalysts with improved characteristics for the production of high-octane gasoline with low sulfur content. New catalytic systems based on alumina and other carriers modified with transition metals, lanthanum and phosphorus were synthesized. By physico-chemical methods of analysis TPD of ammonia, TEM and XRD, we studied the acid–base and structural characteristics of the developed catalysts. The activity of the developed catalysts in the studied process of hydrotreating gasoline fractions depends on the structure and condition of the active centers. The process of hydrotreating straight-run gasoline in the presence of synthesized catalysts was carried out on a laboratory flow unit. It was shown that, during the hydrotreating of straight-run gasoline on the NiO-MoO3-La-P-HZSM-HY-Al2O3 catalyst, the octane number in the final product increased to 88.6, and the sulfur content decreased from 0.0088 to 0.001%. It was found that the minimum sulfur content in the gasoline hydrotreating product of 0.0005% was achieved on the catalyst CoO-WO3-La-P-HZSM-HY-Al2O3, which is significantly lower than for other studied catalytic systems. The obtained results of the sulfur content in the hydrotreating products fully comply with the Euro-5 standard. Thus, the efficiency of hydrotreating the gasoline fractions studied in this work was mainly determined by the nature of the carriers and modifiers used for the synthesis of catalysts and the technological parameters of the process. The synthesized catalysts showed high activity and selectivity, resulting in high-octane gasoline with a low sulfur content that meets international quality standards.

Engineering acidic and Pt sites on WO3- doped H-mordenite supported Pt catalyst for hydrogenation of γ -valerolactone to methyl tetra hydrofuran

The selective hydrogenation of gamma valerolactone (herein after GVL) into 2-methyl tetra hydrofuran (herein after MTHF) was studied over the different tungsten oxide-loaded Pt-doped H-Mordenite catalysts in a vapour phase continuous flow reactor. These catalysts were characterized by XRD, N2 adsorption-desorption analysis, SEM, TEM, FT-IR, Raman, XPS, TPR, NH3-TPD and pyridine adsorbed FT-IR analysis. XRD analysis result suggests that the tungsten oxide was well dispersed at low tungsten oxide loadings and, the tungsten oxide crystallites were formed at higher tungsten oxide loadings and the crystalline structure related to H-mordenite was retained for all the synthesised samples. The nitrogen adsorption-desorption analysis supported this result well. The TEM analysis confirms nano-sized platinum and tungsten oxide formation at 2Pt/10W-HM samples. The ammonia TPD analysis results suggested that all the samples possess weak and strong acidic sites and the amount and strength of acidic sites varies among the samples. The Pyridine adsorbed FT-IR results suggested that all the sample possesses mainly lewis acidic sites. These catalysts were evaluated for synthesising MTHF from GVL under different reaction conditions. Among the various synthesised catalysts studied, the 2 wt% Pt/10W-HM catalyst was identified as an effective catalyst with the 97 % conversion of GVL and the 98 % selectivity of MTHF. The higher catalytic performance depended on the distribution of surface tungsten oxide species along with the suitable acidic properties of the supported system.

INFLUENCE OF MODIFICATION ON PROPERTIES OF ZSM-5 ZEOLITE IN THE REACTION OF TOLUENE ALKYLATION WITH ISOPROPANOL

Bimetallic catalysts based on ZSM-5 zeolite modified with ytterbium and nickel have been prepared. The influence of the concentration of ytterbium (1.7–5.0 wt.%) and nickel (1.0–1.5 wt.%) on the acidic, textural and catalytic properties of the zeolite in the reaction of alkylation of toluene with isopropanol in the temperature range of 300–3500C was studied. It has been shown that the unmodified zeolite HZSM-5 exhibits low selectivity (54.6–58.2%) for isopropyltoluenes (3-IPT, 4-IPT, and 2-IPT) than the modified catalysts. In addition, the content of the valuable 4-IPT isomer does not exceed 44.2%. Modification of HZSM-5 with ytterbium in an amount of 5.0 wt.% leads to an increase in the selectivity for isopropyltoluenes up to 68.7%, and the selectivity for 4-IPT up to 68.8%. Additional modification of the 3%-Yb-HZSM-5 catalyst with nickel in the amount of 1.0 wt.% prevents the formation of 2-IPT and promotes an increase in the yield of 4-IPT. The modified catalysts were characterized by XPA, BET, BJH, and ammonia TPD. Modification, calcination, and successive treatment of the catalyst with air and hydrogen leads to a dispersed distribution of Yb2O3 and metallic nickel oxide nanoparticles in the outer surface and in the pores of the zeolite, which causes a decrease in the specific surface area, total pore volume, and an increase in the fraction of mesopore volume. As a result of the interaction of modifiers with acidic OH groups of the zeolite, the concentration of strong Brønsted acid sites decreases and new, stronger Lewis acid sites form. All this has a decisive effect on the selectivity of 4-IPT formation and the stability of the bimetallic catalyst. The maximum selectivity for 4-IPT on a 3% Yb 1.0% Ni/HZSM-5 bimetallic catalyst is achieved at 3300C and is 71.5% at a toluene conversion of 24.6%.

Facile Synthesis of Ethyl Acetate over ZrO2.TiO2 Mixed Oxide Supported Vanadium Boasted Phosphomolybdic Acid Catalyst at Room Temperature

Initially, mixed oxide of ZrO2.TiO2 support was synthesized by the sol-gel method, and then after vanadium was incorporated, phosphomolybdic acid (VPMA) was synthesized by the hydrothermal method. VPMA supported on ZrO2.TiO2 support of various VPMA loadings that were synthesized by the impregnation method. The structure, surface area, acidity, and morphology of the materials were analysed by X-ray diffraction, BET surface area, ammonia TPD studies, and SEM analysis, respectively. The XRD result shows crystallites of zirconia, titania, and Keggin ion of VPMA catalysts, and also, below 20 wt% of VPMA loading, crystallites of Keggin ion are not observed. BET surface area analysis reveals that increase of VPMA loading, surface area was sharply declined at higher loadings. Ammonia TPD analysis finds that acidity is inclined with VPMA loadings. SEM studies reveal that bulk formation of the active phase is observed at higher loadings. Esterification of acetic acid was tested over VPMA/ZrO2.TiO2 catalyst that exhibited higher activity during reaction than pure VPMA catalyst. These findings were well correlated with surface area and acidity loadings.

Boosting the Hydrodeoxygenation Activity and Selectivity of Ni/(M)-SBA-15 Catalysts by Chemical Alteration of the Support.

The influence of the acid sites in the hydrodeoxygenation of anisole performed over Ni catalysts supported on SBA-15 modified with metal oxides (Ni/M-SBA-15, M = Ti, Zr, Al, or Nb) was demonstrated. Catalysts were characterized by SEM-EDX, nitrogen physisorption, XRD, UV-visible DRS, TPR, TPD of ammonia, IR-Py, O2 chemisorption, and high-resolution transmission electron microscopy. The mesoporous structure and the hexagonal arrangement of the supports were maintained in the catalysts. Ni catalysts supported on modified M-SBA-15 exhibited a higher metal-support interaction, an increase in the acidity and, as a consequence, improved selectivity to cyclohexane. The deoxygenation reaction rate constants increased as Ni/SBA-15 < Ni/Ti-SBA-15 < Ni/Nb-SBA-15 < Ni/Zr-SBA-15 < Ni/Al-SBA-15, which is attributed to the increase in the amount and strength of acid sites, especially of the Brønsted ones, which promotes the cleavage of the C-O bond. It is also important to keep the metal/acid sites together to obtain high activity and selectivity to hydrodeoxygenated products.

Influence of pseudoboehmite properties on characteristics of CoMo/ASA-Al2O3 catalysts for selective hydrotreating of FCC gasoline

The influence of alumina precursor (pseudoboehmites) in CoMo/ASA + Al2O3 catalysts on catalytic activity in FCC gasoline hydrotreating has been studied. Pseudoboehmites prepared by alcoholate, precipitate and hydrothermal technologies were used. Parent powders, supports and catalysts were characterized by low-temperature N2 adsorption, TPD of ammonia, STEM, HRTEM, UV–vis spectroscopy. Catalysts were tested in hydrotreating of the model FCC gasoline feedstock. It is shown that the choice of pseudoboehmite has significant effect on textural, acid and mechanical properties of supports and catalysts, as well as dispersity of the active phase. The type of pseudoboehmite affects the amount of tetrahedral cobalt in catalysts that changes surface activity per 1 g of the catalyst. The linear dependence between the ratio of the medium and weak acid sites and catalyst selectivity was found. It is established that isomerizing activity is higher than the hydrogenating one, when medium/weak acid sites ratio in the catalyst is lower than 1.85.

Shaping Y-Zeolites using in situ formation of alumina and AlPO binders: Coke-resistant catalysts for the cracking of methylcyclohexane

Endothermic catalytic cracking of hydrocarbon fuels over solid acid catalysts has been considered a potential heat sink to offset the thermal loads on high-speed flight vehicles, thus maintaining their catalyst stability and activity. Which is essential as an effective heat sink and produce fuels for sustained flight. The present work demonstrates a novel approach of dispersing zeolite in a catalyst matrix containing inorganic binders such as alumina and aluminum phosphate (ALPO) to improve the thermal, mechanical stability as well as the coke-resistance of Y-zeolites during catalytic cracking of endothermic fuels. Synthesis of such binders modified zeolite was achieved by adding Y-zeolite to pseudo boehmite, an alumina precursor followed by its hydrolysis in the presence of either nitric acid or phosphoric acid, which led to the formation of Alumina or ALPO modified zeolites. During this process, partial removal of alumina from the zeolite framework functions as seed for the growth of alumina and AlPO binders which together form a catalyst matrix consisting of zeolite and binder. Three different Y-Zeolites of varying Si/Al ratios were modified with alumina and ALPO binders using the afore-mentioned process. N2 sorption isotherms, Ammonia TPD, Solid state NMR and SEM imaging showed that these two binders modified the textural, structural, and acidic sites of the zeolites. Catalytic cracking of methylcyclohexane (model endothermic fuel) over these binder modified zeolites was carried out to study their performance and determine the conversion of methylcyclohexane, catalyst stability, product selectivity and coke deposition. Alumina and AlPO binders were observed to have differential binding with the zeolite acid sites, therefore the resultant catalyst activity, product activity and coking behavior were also found to be different. The alumina modified zeolites showed a slight decrease in the catalytic activity but promoted the formation of coke which can be easily oxidized and the selectivity towards cracked products than their isomers. In contrast, AlPO modified zeolites exhibited decreased catalytic activity but also decreased the coking considerably. Spent catalysts characterization clearly demonstrated that the binder modification of zeolites improved the catalyst stability, products selectivity, coke deposition, nature of coke and the amount of coke deposition.

Diels-Alder conversion of biomass-derived furans and ethylene to renewable aromatics over mesoporous titanium phosphate

Metal phosphates such as P-Beta, Zr-P and Sn-P have drawn lots of attention as emerging catalysts for biomass conversion due to its mild acidity which results in high selectivity to the targeted products while minimizing the unwanted side reactions such as coking that are prevalent in reactive biomass-derived compounds. In this study, we have investigated the production of sustainable aromatics such as p-xylene (PX) and toluene (TOL) via Diels-Alder cycloaddition (DAC) of biomass-derived 2,5-dimethylfuran (DMF) and 2-methylfuran (MF) with ethylene over titanium phosphate catalysts. Specifically, the effects of synthesis method (e.g., sol-gel vs hydrothermal), activation method and P/Ti molar ratio on the structural and acid properties of titanium phosphate catalysts were systematically studied to understand the catalytic consequences of the titanium phosphate materials for the DAC of furans. In addition, amphiphilic surfactant was applied to all catalysts for the formation of mesoporous structure. The characterization studies of the prepared catalysts using XRD, BET, FT-IR, XPS, NMR spectroscopy and TPD of ammonia indicated that the degree of Ti-O-P bond formation, catalysts surface area and surface acidity are largely affected by the catalysts synthesis conditions. Overall, the mesoporous titanium phosphate catalyst, synthesized by hydrothermal method at 180 ℃ for 12 h followed by ethanol refluxing at 60 ℃ for 24 h at a molar P/Ti ratio of 1 showed the highest surface area and the highest acid site density which arise from its distinct ordered Ti-O-P bonding structure as evidenced by XPS and NMR. The catalyst demonstrated the remarkably high PX selectivity of > 90 % at the high DMF conversion of > 90 % and the reusability after two successive reaction-regeneration cycles, showing high phosphorus leaching tolerance.

Zeolites mesoporosity evaluation using the cracking of 1,3,5-triisopropylbenzene; a critical assessment

The standard faujasite Y series of Zeolyst International was tested in the catalytic cracking of 1,3,5-Triisopropylbenzene (TIPB) in a continuous-flow fixed-bed catalytic reactor. Textural properties, true density, XRD, TEM, ammonia TPD, and Brønsted acidity by the isopropylamine decomposition reaction were used to characterize the zeolites. TIPB conversion responds to the acidity available to the molecule rather than only mesoporosity. Deactivation behavior gives valuable information about accessibility. Criteria like the initial conversion or at another time are not enough for correctly ranking the catalysts; neither is the selectivity to benzene. TOF and TON are better criteria for classifying the catalysts than selectivity to a specific product like di-isomers. Zeolite CBV780 shows the highest TOF of the series, but zeolite CBV720 gives the highest TON. A good balance between acidity and mesoporosity provides the catalyst with increased activity in the TIPB cracking reaction.

Phosphotungstic acid immobilized over SnO2 mesoporous material as a heterogeneous catalyst for fructose to 5-hydroxymethylfurfural conversion

5-Hydroxymethylfurfural (HMF) is regarded as an essential platform chemical due to its flexible nature that could be converted into a variety of value-added compounds including production of liquid fuels and fine chemicals. We have developed a phosphotungstic acid (PTA) immobilized over SnO2 mesoporous material by hydrothermally employing Pluronic P123 as a structure directing agent (SDA) to obtain a heterogeneous catalyst for fructose to HMF conversion, and the catalyst is designated as MSnPTA. The powder X-ray diffraction patterns in low angle region, type IV isotherm and fringes of the catalyst confirmed the mesoporosity of the material. The catalyst is comprised of BET surface area of 85.86 m2/g and average pore diameter of 7.9 nm. Spherical shape through worm like structure formed small particles facilitated the large surface area of the MSnPTA catalyst that prefer to occur the catalytic reaction. The uniform elemental distribution of PTA over SnO2 ascribed more active sites, resulting in high acidity of the catalyst as measured by TPD of ammonia, which increased the conversion of fructose to high yield of HMF in a short reaction time. The yield of the HMF increased as increasing the amount of catalyst and temperature as expected.

Synthesis and catalytic behavior of FCC catalysts obtained from kaolin by the in-situ method

In-situ zeolites NaY and Na[B]Y were synthesized on microspherical matrices of kaolin to obtain FCC catalysts. An alkaline pretreatment of the matrix was investigated in order to evaluate its effect on matrix properties and crystallization of the in-situ synthetized zeolites. Catalysts were characterized by SEM, TEM, Ar adsorption, XRD and NH3-TPD. It was observed an increase in the surface area and mesoporosity of the alkaline treated catalysts either synthetized with the presence of boron or with no boron in the hydrothermal reaction mixture. Ammonia TPD analyses have shown an increase in the amount and strength of the acidity of the catalysis with the zeolites crystallized on the pretreated matrices and exchanged with lanthanum ions. Thus, a combination between higher concentration of stronger acid sites and higher proportion of mesoporous generated in the matrices treated with alkaline solution had resulted in more active catalyst as shown by the triisopropylbenzene cracking experiments conducted here.Graphical abstract

SBA-15 and carbon supported nickel, heteropoly acid catalysts for the hydrodeoxygenation of lignin derived trans-anethole to sustainable aviation fuel

Catalyst is the key for the hydrodeoxygenation (HDO) of lignin derivatives to produce alkyl aromatics and alkyl cycloalkanes, key components of 100% sustainable aviation fuels (SAF). Mono and bi-functional catalysts of nickel (Ni) and heterophosphotungstic acid (HPW) supported on SBA-15 and carbons were prepared, characterized and evaluated for the HDO of lignin derived trans-anethole. The SBA-15 structure was intact but its surface area and pore volume decreased with the incorporation of Ni and HPW. UV–Visible DRS and XPS confirmed the presence of Nio and Ni2+ in the bi-functional catalysts. FTIR spectra of pyridine adsorbed Ni(10)-HPW(10)/SBA-15 catalyst showed the presence of both Brønsted and Lewis acid (Ni2+) sites and hence its acidity was higher than mono functional HPW/SBA-15 catalyst as indicated by the ammonia TPD studies. The synergy between them might be the possible reason for the higher and stable conversion, higher HDO selectivity, and more importantly higher selectivity for propyl benzene and propyl cyclohexane over bi-functional catalysts. Among the bi-functional catalysts, the highest conversion and HDO selectivity were observed over Ni(10)-HPW(10)/SBA-15. Its highest selectivity for propyl cyclohexane was due to its mean Ni particle size of 31.02 nm, large enough for the co-adsorption of hydrogen and benzene ring of propyl benzene, thus led to its saturation. Optimum temperature for the maximum conversion and HDO selectivity was found to be 400 °C for the bi-functional catalysts. Comparing carbon and SBA-15 supported Ni-HPW catalysts, later have shown higher HDO selectivity owing to strong metal-support interaction.

Ordered mesoporous zirconium silicates as a catalyst for biofuel precursors synthesis

Zirconium incorporated three-dimensional ordered mesoporous silica (FDU-5) catalysts with different Si/Zr (100, 50 and 25) ratios were synthesized using an Evaporation Induced Self Assembly (EISA) method to maximize the incorporation of zirconium sites in the silica framework. The physicochemical properties of the synthesized materials were characterized by several techniques such as XRD, N2 sorption, diffuse reflectance UV–Vis, TEM, ammonia TPD, ICP-OES and pyridine adsorbed FT-IR. The catalytic activity was evaluated in acid-catalyzed esterification of glycerol with acetic acid. The effects of different reaction parameters were studied to optimize the maximum yields, such as reaction temperature, catalyst loading, acid/alcohol molar ratio, and reaction time. Esterification of glycerol with levulinic acid and levulinic acid with ethanol was also performed to synthesize fuel precursors. Reaction results showed that the prepared Zr-FDU-5(25) material was a very high catalytic activity, which depended mostly on the zirconium species' availability on the surfaces and framework. This zirconium containing FDU-5 material was very active in the esterification reaction and selective product formation at certain reaction conditions. The selected catalyst was recycled five times without significant loss in its activity.

Catalytic activity of hierarchical beta zeolites in the Prins cyclization of (−)-isopulegol with acetone

Several hierarchical beta zeolites prepared via hydrothermal treatment of a concentrated zeolite gel-precursor were investigated in Prins cyclisation between (–)-isopulegol and acetone acting as a reactant and a solvent for production of a chromenol compound exhibiting antiviral activity. The catalysts were characterized by SEM, TEM, nitrogen physisorption, ammonia TPD, adsorption-desorption of pyridine and 2,4,6-tri-tert-butylpyridine with FTIR spectroscopy. For the Prins cyclization performed at 30 °C, the highest yield of the desired product was obtained over a zeolite catalyst containing a developed mesoporosity with a uniform mesopore size and an optimum ratio of Brønsted to Lewis acid sites.

Evaluation of nickel-containing zeolites in the catalytic transformation of glucose in an aqueous medium

The transformations of carbohydrates into the platform substances such as furfural, hydroxymethylfurfural (5-HMF), lactic acid, etc. are actual environment-friendly processes. Herein, glucose transformation in an aqueous medium (10 wt.%) at 160 °C over synthesized nickel modified zeolites Y, M and ZSM-5 has been studied. The catalysts have been characterized by using FTIR spectroscopy, pyridine adsorption with IR-spectroscopic control, ammonia TPD, low-temperature nitrogen adsorption/desorption, and TEM. Utilizing HPLC, GC and 13C NMR the reaction products were identified. The 5-HMF molar yields over 5NiHY, 5NiHZSM-5, and 5NiHM were 8.5, 14, and 16%, respectively. Glucose conversion was practically quantitative. To investigate deactivated samples, FTIR and DTA/TG techniques have been used. The 5NiHM and 5NiHZSM-5 catalysts have showed a twice-lower weight of deposits (10 wt.%) than 5NiHY with the biggest total acidity. Bifunctional Lewis/Bronsted acid zeolite catalysts with Lewis acidity predominance demonstrate better performance in glucose transformation. The balance between acidity of the catalyst and textural properties is stated to play a key role in the transformation of glucose into 5-HMF. Nickel-containing zeolite ZSM-5 and M can be considered as promising catalysts for glucose conversion. Perspective trends in related research are provided.

Platinum catalysts supported on ZSM5 zeolites with a hierarchical pore structure: characterization and performance in n-hexadecane hydroconversion

HZSM5 zeolites with a hierarchical pore structure were prepared from a microporous one using the top-down methodology by treatment with a sodium hydroxide solution in optimal conditions of time, alkali concentration and temperature. These materials were used as supports for platinum to produce bifunctional hydroconversion catalysts. The activity in n-hexadecane hydroconversion was one order of magnitude larger on Pt supported on the mesoporous than on the untreated zeolite and one order of magnitude larger than that of the supports. All Pt catalysts and supports were more selective to hydrocracking than to hydroisomerization, but the initial selectivity for hydroisomerization of the Pt catalysts supported on the mesoporous supports was considerably smaller than that of all other materials, including the supports. This was attributed to a smaller mass transfer limitation with the Pt catalysts supported on the mesoporous zeolites. All supports and catalysts were extensively characterized by techniques such as X-ray diffraction, hydrogen chemisorption, TPD of ammonia, IR spectroscopy of adsorbed pyridine, MAS 29Si and 27Al solid state NMR and transmission electron microscopy.

A novel approach of methane dehydroaromatization using group VIB metals (Cr, Mo, W) supported on sulfated zirconia

AbstractMethane dehydroaromatization (MDHA) is a direct activation approach to covert methane to value-added chemicals in a single step. This requires no intermediate step, making it a commercially economic approach. Mo supported on HZSM-5/MCM-22 is a well-studied catalyst for this reaction, where Mo sites are responsible for activating methane to C2Hy dimers, which can oligomerize on HZSM-5 Bronsted acid sites to produce aromatics. Challenges for these bifunctional catalysts involve rapid coking and low product yield. In this study, a novel catalytic approach is introduced using group VIB metals (Cr, Mo, W) supported on sulfated zirconia (SZ) solid acid. It is believed that the Bronsted acidity of SZ should help to convert the dimers generated from metal sites to ethylene and aromatics like benzene.Here, fresh Mo, W and Cr were doped into SZ and characterized using pyridine DRIFTS, ammonia TPD, BET and SEM-EDS.. Catalytic activity for MDHA was ranked as Mo&gt;W&gt;Cr. Mo/SZ showed greater selectivity towards ethylene and benzene, followed by W/SZ, which was selective primarily towards ethylene. Cr/SZ showed the least activity under similar reaction conditions, producing only a small amount of ethylene. Higher catalytic activity for Mo/SZ was possibly due to reduced Mo oxide sites, found from XANES analysis, as well as higher acidity, observed from TPD. Deactivation was mainly due to coking, observed from subsequent TPO analysis. Further investigation is necessary to enhance the activity of this novel catalytic approach before considering for potential industrial applications.

Direct conversion of methane to C2 hydrocarbons using W supported on sulfated zirconia solid acid catalyst

One of the most challenging aspects of modern day catalysis is the activation of methane. Conventionally, methane is activated with oxidizing agents to produce syngas, which then reacts to produce high value hydrocarbons. This process is energy inefficient. A more economic process is the direct one-step activation of methane to form value-added chemicals. This report focuses on direct conversion of methane to ethylene and ethane. Ethylene and ethane are the most important feedstocks in modern day chemical industries. Conventional process for ethylene production is via steam cracking of hydrocarbons, which is not an energy efficient approach. A direct conversion route from methane to C2 hydrocarbons would be a significant advance and has been widely studied. Mo supported on solid acids have been previously reported to be promising for direct conversion of methane to higher hydrocarbons. Here, a novel catalytic approach is introduced with W, a strong oxidizing agent, doped on sulfated zirconia solid acid and studied for the activation of methane at 650–750 °C. BET, DRIFTS, ammonia TPD, XPS, XRD and SEM–EDX were used to characterize the fresh catalyst. Reaction products are primarily ethylene and ethane, along with trace aromatics. Methane activation along with production of C2 hydrocarbons increased noticeably at higher temperature but deactivated due to carbon deposition as confirmed by TPO.

Zeolite-based catalysts for the removal of trace olefins from aromatic streams

Removal of trace olefins from aromatic liquids was investigated on UZM-8 and MCM-22, which are the family of MWW zeolites. Both these zeolites were synthesized with similar Si/Al ratio and characterized by various techniques such as XRD, SEM, ICP, N2 adsorption, Ammonia TPD and solid-state MAS-NMR. Olefin conversion activity over UZM-8 was found to be significantly higher than that of MCM-22. In addition to this, deactivation of UZM-8 was slower than the MCM-22. UZM-8 with irregular stacking of MWW layers possess high external surface area and exposes more number of active sites to the reactant molecules. Mesopores generated due to the disordered layers of UZM-8 allows the fast diffusion of the substrate molecules in which pore clogging does not occur, thus making it more active and slow deactivation than that of MCM-22.Graphic abstract

Isoprene Synthesis from Formaldehyde and Isobutylene in the Presence of Aluminum- and Niobium-Containing BEA Catalysts

A single-stage gas-phase synthesis of isoprene from formaldehyde and isobutylene in the presence of Al–BEA and Nb–BEA zeolite catalysts containing different amounts of aluminum and niobium has been studied. The physicochemical properties of the catalysts have been studied by low-temperature nitrogen adsorption, infrared spectroscopy of adsorbed CO, X-ray fluorescence analysis, and ammonia TPD methods. Catalytic tests have shown that, at similar formaldehyde conversion values, the isoprene selectivity is higher in the presence of the Al-containing BEA catalysts. It has been found that Al–BEA with Si/Al = 12 exhibits the highest activity in isoprene synthesis.