Strong Bronsted Acid Sites Research Articles

STUDY OF CATALYTIC BEHAVIOURS OF THE SPINEL STRUCTURE NdxMg1- xAl2O4 COMPOSITION WITH ZSM-5 ZEOLITE IN ETHYLBENZENE DISPROPORTIONATION

Nanosized (10–15 nm) powders of spinel structures NdxMg1–xAl2O4 were obtained by low-temperature combustion of aluminium, magnesium, neodymium nitrate solutions, diethylmalonate, and hydrazine monohydrate with further calcination of nanopowders at 1000 °C, which were used in the preparation of catalytic compositions with ZSM-5 zeolite. The obtained catalytic compositions were characterized by X-ray diffraction, pyridine adsorption, and low-temperature nitrogen adsorption. The acidic properties and porosity of the catalysts were altered by controlling the concentration of nanopowder (1.0–7.0 wt.%) in the catalytic composition. The interaction of the modifier with HZSM-5 zeolite leads to a decrease in specific surface area and pore volume, as well as reduse of strong Bronsted acid sites (B) and an increase in the concentration of medium Lewis acid sites (L), resulting in a change in the B/L ratio from 3.61 to 0.23. The ongoing variations contributed mainly to an enhancement of the para-selectivity of the catalytic composition in the ethylbenzene disproportionation reaction. The catalytic composition of 5% Nd0.1Mg0.9Al2O4 with a pore volume of 0.15 cm3/g and an acid site B/L ratio of 0.27 demonstrates a maximum selectivity to p-diethylbenzene of 75.6% with a conversion of ethylbenzene of 23.7%.

Continuous-flow reductive etherification of furfural over CuAlOx catalyst combined with HZSM-5-Al2O3 composite

Furfuryl alkyl ethers (FAEs) are considered attractive biofuels or gasoline additives. Reductive etherification of bio-based furfural (FF) is a promising method for production of these compounds. In present work, we study the catalytic behavior of Cu-Al mixed oxide in combination with HZSM-5-Al2O3 composites for the syntheses of FAEs in a flow reactor using H2 as a reducing agent. The Cu-based catalyst ensures the hydrogenation of FF to furfuryl alcohol, which then reacted with alcohol in the presence of the acid catalyst. It was found that the reaction of FF with 2-propanol over catalytic system including HZSM-5(Si/Al = 40)-Al2O3 leads to the formation of 2-(isopropoxymethyl)furan (IMF) in excellent yield due to the optimal concentration of strong Bronsted acid sites in the composite. Lower selectivity to IMF was observed in the presence of HZSM-5 with Si/Al ratio of 15, 25 and 140. In addition, the use of primary alcohols instead of 2-PrOH gives a significantly lower yield of FAEs.

Designing main-group catalysts for low-temperature methane combustion by ozone

The catalytic combustion of methane at a low temperature is becoming increasingly key to controlling unburned CH4 emissions from natural gas vehicles and power plants, although the low activity of benchmark platinum-group-metal catalysts hinders its broad application. Based on automated reaction route mapping, we explore main-group elements catalysts containing Si and Al for low-temperature CH4 combustion with ozone. Computational screening of the active site predicts that strong Brønsted acid sites are promising for methane combustion. We experimentally demonstrate that catalysts containing strong Bronsted acid sites exhibit improved CH4 conversion at 250 °C, correlating with the theoretical predictions. The main-group catalyst (proton-type beta zeolite) delivered a reaction rate that is 442 times higher than that of a benchmark catalyst (5 wt% Pd-loaded Al2O3) at 190 °C and exhibits higher tolerance to steam and SO2. Our strategy demonstrates the rational design of earth-abundant catalysts based on automated reaction route mapping.

Synthesis and efficient use of low‐cost natural red clay catalyst for the production of upgraded fuel oil using pyrolysis of waste expanded polystyrene and in situ vapour phase hydrogenation

The waste expanded polystyrene (WEPS) was subjected to the pyrolysis and in situ hydrogenation process in a laboratory fabricated innovative reactor on a red clay catalyst in the temperature range of 400°C to 700°C. Five different catalysts were synthesized from the eco-friendly and non-toxic red clay, that is, red clay in natural form (RC), red clay calcined at 600°C (RC-600), red clay calcined at 700°C (RC-700), red clay calcined at 800°C (RC-800), and red clay calcined at 900°C (RC-900). The catalytic pyrolysis of WEPS, in situ hydrogenation, and aromatization were performed keeping the synthesized catalyst in different reactor arrangements, that is, liquid phase/X-type, vapour phase/Y-type, and multiphase/XY-type. The raw and calcined red clay catalysts were characterized by various characterization techniques such as SEM-EDX, BET, XRD, and FTIR. The calcination temperature greatly influenced the surface morphology and surface area of the red clay catalysts. The surface morphology of calcined red clay catalyst RC-800 shows nano cluster form of particles with very high porosity. The highest surface area of 29.25 m2/g and highest silica content of 56.82 wt% were found for the RC-800 catalyst. Furthermore, the XRD analysis ensured the presence of illite-micas, α-quartz, κ-kappa alumina, δ-delta alumina, and θ-theta alumina in the RC-800 catalyst only. The presence of strong Bronstedacid sites in RC-800 catalyst was confirmed by the FTIR analysis. The highest liquid yield of 94.37 wt% was obtained for the thermal pyrolysis of WEPS at the optimum temperature of 650°C and heating rate of 15°C/min. The maximum BTE content of 11.38 wt% was recorded for the pyrolysis oil obtained from the thermal pyrolysis of WEPS at the same optimum conditions. On the other side, the highest liquid yield of 88.82 wt% was obtained for the X-type pyrolysis at the optimum temperature of 600°C and heating rate of 15°C/min using red clay catalyst RC-800. The Y-type and XY-type pyrolysis produced maximum liquid yield of 80.81 wt% and 79.47 wt%, respectively, at the optimum temperature of 550°C and at heating rate of 15°C/min using the same red clay catalyst RC-800. However, the multiphase/XY-type pyrolysis produced the highest BTE content of 27.62 wt% and lowest styrene content (60.75 wt%) at a temperature of 550°C using RC-800 catalyst among all types of pyrolysis. The maximum styrene content of 84.74 wt% was found in pyrolysis oil obtained from thermal pyrolysis of WEPS at optimum conditions. The styrene content obtained reduced significantly from 68.83 wt% to 60.75 wt% when the reactor arrangement was changed from X-type to XY-type. The pyrolysis oil obtained from XY-type/multiphase pyrolysis was found suitable for the use in internal combustion (IC) engine.

Efficient Bifunctional Catalysts for Enhanced Carbon Conversions and Alky-Aromatics Production in Crude Bio-glycerol Methanol Processes

The present study reports the development of an alkali earth metal (Ba)-modified Zn/ZSM-5 catalyst for efficient carbon conversion of bio-derived crude glycerol toward aromatics production in a methanol (GMTA) co-process. The metal functionality caused considerable alteration in acidity to improve the dehydrogenation properties of the catalyst to produce more aromatics and to simultaneously control the undesired cracking reactions responsible for the gas product formation. The methanol concentration in the feed mixture was also observed to influence the carbon conversions toward liquid and gas products, especially aromatics. At optimized reaction conditions, the 0.1Ba-1Zn/ZSM-5 catalyst produced 69C% high-value gasoline blending stock possessing ∼57C% aromatics and ∼116 research octane number suitable for fuel applications. The aromatics formation was accompanied by 28 mol % of H2 as a valuable byproduct. XRD, FT-IR, and 27Al-NMR studies confirmed the structural integrity of ZSM-5 even after metal loading treatments. XPS and UV–Vis DRS spectra confirmed the presence of Zn in the form of (ZnOH)+ species. NH3-TPD and pyridine-IR studies revealed a decrease in the strong acidity of ZSM-5 along with a simultaneous increase in Lewis acidity. Thus, the enhanced carbon conversion and aromatics yield in the GMTA process observed on 0.1Ba-1Zn/ZSM-5 might be understood by two main factors, namely, (i) decreased strong Bronsted acid sites to suppress undesirable cracking reactions and (ii) increased Lewis acid sites to promote dehydrogenation reactions.

Short review on heteropoly acid based catalyst for valorization of biomass waste into valueable chemicals

Depletion of fossil fuels resources has triggered more research on finding potential alternative sources that are more sustainable such as biomass waste. However, deconstruction of the complex biomass waste into desired products is too challenging and usually require a strong catalyst with a great hydrolysing property. Common acids such as sulphuric acid, hydrochloric acid and nitric acid were the most studies for biomass conversion. These liquid acids catalysts suffer low recovery and recyclability that can be overcome by a solid acid catalyst. Heteropoly acid (HPA) catalyst is the preferred choice to replace these common acid catalysts as it is known to have a strong Bronsted acid site with an oxidizing property that allows this catalyst to hydrolyse and oxidize in one-step reaction. Furthermore, heteropoly acid (HPA) catalyst can be modified into heterogenous type of catalyst by solidifying HPA to increase the surface area and recyclability. Future work of this research is necessary to improvise the previous method of the catalyst preparation and to suppress the by-products after the catalytic process. In this review, we summarize the use of HPA catalyst in the complex reaction process of biomass conversion to valuable chemical products.

Aromatization of n-pentane over Zn/ZSM-5 catalysts: effect of Si/Al ratio and reaction pathway

The metal modified ZSM-5 catalysts has been widely used in the aromatization of light alkanes. To investigate the effect of Si/Al ratio of ZSM-5 zeolites, a series of Zn/ZSM-5 catalysts with different Si/Al ratios have been prepared by wet impregnation and tested for n-pentane aromatization. The results indicated that, the introduced Zn species consumed the strong Bronsted acid sites and inhibited the undesired cracking reactions effectively. With the increase of Si/Al ratio of ZSM-5 zeolites, the n-pentane conversion decreased obviously due to the reduced acid content and strength, while the selectivity to BTX remained almost unchanged. Attributed to the weakened cracking and hydrogen-transfer reactions with increasing Si/Al ratio, the selectivity to light alkanes decreased, while that to olefins increased remarkably. Further, the possible reaction pathways have been proposed to better elucidate the changing product distribution with the Si/Al ratios.

Oxidative dehydrogenation of n-octane using Ba and Ga-modified faujasite type catalysts prepared by different methods

Ionic exchange and isomorphic substitution were used for the synthesis and modification of faujasite (zeolite and silicalite Y) catalysts. These two methods were used to synthesize 1 wt% extra-framework and framework gallium modified faujasite zeolites respectively, with a Si/M ratio of 2.6, where M = Al and/or Ga. For the silicalite catalyst, 3.5 wt% of Ga was used to maintain the Si/Ga ratio. A series of BaY, Ga-BaY(IS) and Ga-BaY(Sil) were prepared by isomorphic substitution, where (IS) and (Sil) represent Isomorphic Substitution and Silicalite respectively. Ga-BaY(IE) and BaGa-NaY(IE), were prepared by ionic exchange (IE) using the synthesised BaY and a commercial NaY for the latter. For all the prepared catalysts, barium was kept constant at about 4.2 wt% except for BaGa-NaY(IE), where Ba was 1.4 wt%. For the sodium containing catalysts, Na was 10.3 wt%. Pyridine IR and chemisorption techniques showed that the catalysts prepared had more Lewis acid sites compared to Bronsted acid sites. The Na containing zeolite had the highest total acidity compared to those containing only Ba. Aluminium free silicalite contained the least total acidity, which is consistent with previous studies. Catalytic data at iso-conversion (7 ± 1%) showed that the Ba incorporated by ionic exchange zeolites and the silicalite were more selective to octenes (36 and 33% respectively) and less selective to COx (35 and 33% respectively) compared to the isomorphically substituted Ba catalysts. Selectivity to cracked products was reduced when aluminium, responsible for the strong Bronsted acid sites, was eliminated from the synthesis.

Alkylation of Toluene with Isopropanol on Lantanum Modified ZSM-5 Zeolite

The effect of lanthanum concentration on the physicochemical and catalytic properties of HZSM-5 zeolite in a reaction of toluene alkylation with isopropanol was studied in a temperature range of 250–350°C. Based on the data obtained by X-ray diffraction analysis, low-temperature nitrogen adsorption (BET method), and IR spectroscopy, it was shown that an increase in lanthanum concentration in HZSM-5 from 1.0 wt % to 7.0 wt % reduces both the specific surface area and the pore volume of the zeolite despite the retention of its crystalline structure. This also results in redistribution of acid sites, specifically decreases the concentration of strong Bronsted acid sites (B) and increases that of moderate Lewis acid sites (L), thus decreasing the B/L ratio from 3.53 to 0.20. All these occurrences have a crucial effect on the selectivity of reaction products and, in particular, on the p-isopropyl toluene (4-IPT) selectivity. Maximum selectivity, making up 72.4%, is achieved by a zeolite containing 5.0 wt % lanthanum at a B/L ratio of 0.25.

Mesopore-selective incorporation of strong Brønsted acid catalytic sites via aluminium grafting on hierarchically porous siliceous MFI zeolite

Abstract Post-synthetic Al grafting onto the surface silanols in mesoporous MFI zeolite has been investigated in an attempt to obtain a model catalytic material that possesses strong Bronsted acid sites at mesopore surfaces of the zeolite, but not inside the microporous framework. To this end, a siliceous MFI zeolite with a mesopore/micropore hierarchy was synthesized using a meso-micro dual structure-directing diammonium surfactant. The hierarchically porous zeolite was treated with anhydrous AlCl3 for the formation of Si–O–Al bonding with silanols on the mesopore surfaces. According to solid-state 31P NMR spectroscopy of the surface-adsorbed phosphine oxides and catalytic activity for decalin cracking, the Al-grafting treatment performed in the conventional manner resulted in the formation of weak Bronsted acid sites, similar to Al grafting on SBA-15 mesoporous silica. To obtain strong Bronsted acid sites, we have developed a method of heating the AlCl3-grafted zeolite in a controlled-humidity chamber before calcination. The resultant zeolite was catalytically active for cracking of hydrocarbons requiring strong acid sites, but not for methanol-to-hydrocarbon conversion. The results support that the moisture treatment caused a local reconstruction of the initially grafted Al–O–Si framework portion to a strong Bronsted acid site. In addition, our model catalytic zeolite material unveiled the catalytic activity of Bronsted acid sites at the mesopore surfaces in hierarchically porous zeolite in n-octane cracking. Furthermore, we confirmed that this method was effective for other mesoporous MFI zeolites obtained through a post-synthetic desilication route.

Untangling the role of the organosilane functional groups in the synthesis of hierarchical ZSM-5 zeolite by crystallization of silanized protozeolitic units

Abstract Crystallization of hierarchical ZSM-5 zeolite has been performed under hydrothermal conditions from silanized protozeolitic units. The role of amine and phenyl groups present in the organosilanes, as well as the use of dipodal silanization agents, on the creation of mesoporosity in the zeolite samples has been investigated. The presence of amine groups and dipodal moieties in the organosilane increases their interactions with the protozeolitic nanounits in the gel, which results in hierarchical zeolites showing enhanced secondary porosity and a higher degree of modification of the textural properties. Nevertheless, dipodal organosilanes hinder strongly the aggregation of the nanounits, leading to non-completely crystalline materials. In contrast, the combination of phenyl and amine groups into a single organosilane has shown to be effective for the generation of more uniform mesopores. Thus, N-(2-N-Benzylaminoethyl)-3-aminopropyltrimethoxysilane (Ph-2A) has been found as the best silanization agent, affording a hierarchical zeolite with a narrow mesopore size distribution and a high concentration of strong Bronsted acid sites. Moreover, during LDPE catalytic cracking in TGA tests, the latter material allowed the conversion of the polymer to occur in a narrow temperature range as a consequence of its more uniform acid and textural properties. Likewise, this sample exhibited a high activity in LDPE cracking at 340 °C using a laboratory scale reaction system to produce mainly gasoline-range hydrocarbons and light olefins.

Preparation of mesoporous Beta zeolite by fluoride treatment in liquid phase. Textural, acid and catalytic properties

Abstract Beta zeolite (nominal Si/Al = 19) has been treated with HF/NH4F solutions under different HF concentration, temperature and reaction time. It has been found that the crystallinity of the resulting materials is >80% for HF concentration up to 0.5 M, but it drops below this value for the most severe condition (HF = 1 M and 40 °C). The treatment dissolves selectively aluminum, in such a way that the Si/Al increases to 34 for the most attacked material. As a consequence of these treatments, the mesopore volume increases by up to 80% respect to the parent Beta for samples retaining high crystallinity, corresponding to newly created mesopores in the range of 5–20 nm. Detailed STEM-HAADF studies reveal that the chemical attack of the Beta crystals by the acidic fluoride solution progresses slowly along the crystals, leaving behind highly corroded and porous “sponge-like” crystals where the structure of the zeolite is nevertheless retained. Pyridine adsorption/desorption experiments show that a fraction of the extraframework Al present in the starting Beta is reinserted in framework sites, a process that would be mediated by aluminum-fluoride soluble species. As a consequence of this process, the Bronsted/Lewis ratio of the strong acid sites increases from 1 in the starting Beta to close to 3. The concentration of total and strong Bronsted acid sites associated to framework Al increases with the treatment. However, the activity of the samples in the isomerization/disproportionation of m-xylene is lower than that of the parent Beta zeolite, a result that could be due to the higher B/L ratio.

ZSM-5 surface modification by plasma for catalytic activity improvement in the gas phase methanol-to-dimethylether reaction

Abstract Dimethylether (DME) is nowadays considered as one of the most promising alternative fuels for the future. It has a very low climate impact, and can be produced in a renewable way, namely from the gas phase condensation of methanol over common acid catalysts such as γ-Al2O3 or zeolites. The challenge today is to switch from high reaction temperatures (300–350 °C) to lower ones (ideally 100–150 °C) in order to operate more energy-efficiently and with 100% selectivity to DMEThe methanol conversion needs to be increased below 300 °C in order to get high yields of DME even in that low temperature range. In the present paper, we show a way to achieve this in the case of the widely studied ZSM-5 zeolite. We show that submitting the zeolite to a cold plasma treatment before using it as a catalyst allows significantly increasing the yield of DME up to 300 °C. Indeed, the plasma treatment leads to a partial dealumination of the zeolite and thereby to an increase of the number of strong Bronsted acid sites which play a key role in the methanol-to-DME reaction mechanism.

A Comparative Study of n-Butane Isomerization over H-Beta and H-ZSM-5 Zeolites at Low Temperatures: Effects of Acid Properties and Pore Structures

The influences of acidic properties and pore structures of H-Beta and H-ZSM-5 zeolites on the reaction properties of n-butane isomerization at low temperatures were investigated. The results showed that bimolecular pathway of n-butane conversion predominates over H-ZSM-5 zeolites, while the monomolecular and bimolecular pathways occur simultaneously over H-Beta zeolites. The conversion rate of n-butane strongly relies on the amount of strong Bronsted acid sites regardless of zeolite topology. However, the topology of zeolites crucially determines the products distribution, and the density of strong Bronsted acid sites plays a secondary role. The cavities of zeolites, formed in the intersections of channels, provide the places for the bimolecular reaction. The formation of trimethyl C8 intermediates is spatially restricted in the narrow channel intersections of H-ZSM-5 zeolites, resulting in higher contribution of n-butane disproportionation reaction. In addition, the narrow pore channels of H-ZSM-5 zeolite limit the monomolecular isomerization of n-butane molecules and affect the diffusion of heavier products (pentane) produced from bimolecular reaction, leading to the severe secondary reaction and high selectivity to propane. In contrast, the pore channels of H-Beta zeolite allow the monomolecular isomerization of n-butane and the deposition of coke. The topology of zeolites crucially determines the products distribution.

Rhodium–Chitosan Composites Supported on Magnesium–HZSM-5 in the Conversion of Dimethyl Ether to Lower Olefins

The catalytic properties of composite catalyst systems based on zeolite HZSM-5 modified with magnesium, rhodium, and chitosan have been studied. The introduction of a rhodium–chitosan composite has a significant effect on the catalytic properties of the zeolite catalyst providing a significant increase in the activity and stability of the catalyst. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) has revealed that the use of chitosan leads to a decrease in the total acidity of the zeolite catalyst mostly owing to a decrease in the number of strong Bronsted acid sites. It has been shown that the pretreatment of Mg–Rh*chitosan–HZSM-5 with synthesis gas leads to an increase in the time-on-stream stability of the catalyst.

Effect of acidity and porosity of hierarchical HBEA zeolite on catalytic stability of α-methylnaphthalene isomerization

Hierarchical HBEA catalysts were fabricated through alkaline treatment and evaluated in a fixed-bed reactor. The relative crystallinity, pore property, Si/Al molar ratio, coke formation and structure of catalysts were investigated by the methods including X-ray diffraction, N2 physisorption, X-ray fluorescence, thermogravimetric analysis and transmission electron microscope, respectively. The acidity of catalysts was studied by Fourier transform infrared spectrometry using pyridine as the probe molecule. These results demonstrated that pure NaOH treatment improved the mesoporosity of catalyst, while decreased the β-methylnaphthalene selectivity and catalyst stability due to the partially destroyed framework and an increase in the concentration of Lewis acid sites. The Lewis acid sites are responsible for the hydride transfer and subsequent reaction that form coke. In contrast, the presence of tetra-propyl-ammonium hydroxide in the mixed-alkali treatment resulted in regular mesopores development, preserved intrinsic zeolite properties and Lewis sites proportion, leading to the maintained β-MN selectivity and coke deposition rate. The increased mesoporosity and strong Bronsted acid sites amount per number of coke were responsible for the improved coke tolerance of mixed-alkali treated HBEA, and thus its deactivation rate was 41.7% lower than that of HBEA catalyst.

Novel ionic liquid-templated ordered mesoporous aluminosilicates: Synthesis, characterization and catalytic properties

Abstract Highly crystalline ordered mesoporous aluminosilicates with hexagonal AlIITM-41 and cubic AlIITM-48 pore symmetries with varying silicon-to-aluminium ratios were hydrothermally synthesized, for the first time, using long-chain ionic-liquid (IL) such as 1-hexadecyl-3-methylimidazolium chloride (HDMIC), as structure directing agent. The prepared materials were systematically characterized by various analytical, spectroscopic and imaging techniques, viz., XRD, BET, TEM and XRF. In addition, the extent of aluminium incorporation and the nature of acid sites were deduced from 27 Al MAS-NMR and NH 3 -TPD measurements. The structural and physico-chemical properties of both AlIITM-41 and AlIITM-48 were compared with analogous AlMCM-41 and AlMCM-48, respectively prepared using hexadecyltrimethylammonium bromide (CTAB). It was found that all the ionic liquid-templated materials, viz., AlIITM-41 and AlIITM-48, and exhibited large surface area, high crystallinity and thicker pore walls. The observed superior orderness of AlIITM-41 and AlIITM-48 could attribute to a well distributed positive charge and π-π stacking of aromatic imidazolium head group of ionic-liquid. In addition, it also assisted in the incorporation of all the aluminium species exclusively in the tetrahedral silicate framework even after the calcination as confirmed by 27 Al MAS NMR. AlIITM-41 and AlIITM-48 possess more medium and strong Bronsted acid sites due to their thicker walls, high crystallinity and presence of tetrahedral aluminium in the framework, due to which they exhibited higher catalytic activity towards tertiary butylation of phenol with a good Para tertiary butyl phenol selectivity compared to commonly used aluminosilicates, H-AlMCM-41 and H-AlMCM-48.

Alteration of fine fraction of bentonite from Kopernica (Slovakia) under acid treatment: A combined XRD, FTIR, MAS NMR and AES study

Abstract Acid activation of clay minerals is one of the most effective methods proposed to produce materials with increased acidity and adsorption properties. In this work fine fraction of bentonite from deposit Kopernica (Slovakia) was treated with 6 mol/L HCl. Variety of methods were employed in order to investigate the structural changes occurring as a result of the acid activation. Quantitative XRD analysis and FTIR revealed a dominant presence of montmorillonite, with K-feldspars, quartz, volcanic glass, opal C, ferrihydrite, biotite and kaolinite admixtures in acid untreated sample. 29Si MAS NMR spectra also confirmed accessory siliceous phases. 27Al MAS NMR showed that approximately 10% of Al was bound in the tetrahedral sites of montmorillonite. Gradual decrease of the Al, Fe and Mg content, an upward shift of the complex Si O stretching band and the appearance of Q4(0Al), Q3(1OH) signals in the 29Si MAS NMR spectra of the extensively reacted materials indicated a substantial modification of the montmorillonite layers and formation of an amorphous silica product. The accessory minerals quartz, K-feldspars and kaolinite were dissolved more slowly. The presence of kaolinite and quartz/K-feldspars in solid product was confirmed even after treatment for 36 h. The acid treatment affected also the surface and acidity characteristics of the samples. The total specific surface area (EGME SSA) gradually decreased with decreasing montmorillonite content in the reaction product. In contrast, the changes in the N2BET SSA showed that reaction with an acid first increased it to a maximum after treatment for 6 h, but more extensive treatments had a negative effect. After pyridine adsorption the IR spectra of the samples treated for 1 up to 6 h showed, in addition to the bands related to the H-bonded and physisorbed pyridine, also the diagnostic band of pyridinium cation near 1540 cm−1 confirming the presence of strong Bronsted acid sites.

Improving activity of ZSM-5 zeolite catalyst for the production of monomeric aromatics/phenolics from hydrolysis lignin via catalytic fast pyrolysis

This work aimed to further enhance the activity of ZSM-5 zeolite catalyst for the production of monomeric aromatics/phenolics from hydrolysis lignin via catalytic fast pyrolysis. To this end, various treatment approaches including acidification with H2SO4 and H3PO4 and metal (Ni) loading were performed on the ZSM-5 zeolite. Catalytic fast pyrolysis (CFP) of hydrolysis lignin (HL) was conducted at 450 ᵒC using ZSM-5 zeolites with various strengths of acidity (ZSM-5 and Ni-ZSM-5 with moderate Lewis and Bronsted sites, H2SO4-ZSM-5 and H3PO4-ZSM-5 with more Bronsted sites). The results show that the yield of monomeric aromatic compounds increased considerably by increasing the Bronsted acid site and total acidity of the catalyst. With the best catalyst, H2SO4-ZSM-5, the total monomeric aromatics/phenolics yield increased to 151 mg/g-HL, compared to 68 mg/g-HL without catalyst, 84 mg/g-HL with ZSM-5, 96 mg/g-HL with H3PO4-ZSM-5, and 85 mg/g-HL with Ni-ZSM-5. The H2SO4-ZSM-5 demonstrated to be thermally stable and has superb resistance to carbon/coke deposition, owing to its microporous structure, relative large BET surface area and presence of strong Bronsted acid sites.

Propan-2-Ol (Isopropanol) Conversion to Propene and Acetone Over V<sub>2</sub>O<sub>5</sub> Catalysts Supported on Activated Carbon (AC)

The study of the reaction of the conversion of isopropanol at atmospheric pressure and under inert gas was carried out on a series of vanadium catalysts and on a porous support activated carbon prepared from vegetable waste (dates). This reaction competitively produces acetone and propene; it is widely used as a test reaction to study acidic and basic sites. The decomposition of isopropanol occurs by two parallel reactions, the dehydration requires strong Bronsted acid sites giving olefin (propene) and the dehydrogenation is done either in basic sites or in a basic acid pair, either in a redox couple. All samples were characterized by different techniques: FT-IR, DRX, SEM-EDX, and SBET.