Transalkylation of Toluene with 1,2,4-Trimethylbenzene over Large Pore Zeolites

Using industrially relevant operating parameters, the transalkylation of 1,2,4-trimethylbenzene (TMB) with toluene was studied. The effect of acidity and structure, increased reaction pressure, and very low levels of Pt impregnation have been investigated over both H-form and Pt-loaded zeolites: Beta, MOR, and Y. A fixed bed reactor was used at WHSV of 5 h–1, 400 °C, and a 50:50 wt % toluene:TMB ratio with the order of activity after 50 h TOS of Y > Beta ≫ MOR at 1 bar. At elevated pressure (10 bar), all catalysts showed better performance with significant improvement in MOR as pore blockage reduced and the order of activity was Beta > MOR > Y. Incorporation of Pt (0.08 wt %) further improved the activity of all catalysts with the highest conversion after 50 h TOS over Beta (62 wt %) where Beta and MOR yielded similar levels of xylenes (40 wt %). All catalysts were further optimized for activity while maintaining the desired stability and highest xylenes yield

Low-field 2D NMR relaxation and DRIFTS studies of glucose isomerization in zeolite Y: New insights into adsorption effects on catalytic performance

Sn and Ga doped zeolite Y catalysts were tested for the isomerization of glucose to fructose carried out in different solvents (water, methanol and ethanol). Therein, ethanol favoured a Lewis acid site catalyzed pathway that promotes glucose isomerization to fructose, whereas methanol resulted in an equal distribution of products (mannose, fructose and alkyl fructoside). In contrast, the catalysts were totally inactive in water solvent. NMR relaxation measurements, including solvent displacement experiments, suggested that the lack of catalytic activity in water is due to the strong adsorption of this solvent within the zeolite pores blocking reactants from the Lewis acid sites active for the sugar isomerization. In comparison, ethanol adsorbs relatively more strongly than methanol, hence is retained in the pores where solvated fructose is preferentially prevented from the further reaction on Bronsted acid sites situated outside of the pore space. NMR relaxation measurements using pyridine and tetrahydrofuran (THF) and pyridine-DRIFTS measurements suggest metal doping had little effect on the overall relative acid strength of the zeolites but resulted in zeolites with increased Lewis acid strength relative to the non-doped zeolites. The results reported provide direct experimental evidence on the importance of adsorption properties of solvents within zeolites used for glucose to fructose isomerization and may serve as a starting point for a new approach towards designing and optimizing such catalytic systems. & COPY; 2023 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

Assessing the surface modifications following the mechanochemical preparation of a Ag/Al2O3 selective catalytic reduction catalyst

The surface modification of a mechanochemically prepared Ag/Al2O3 catalyst compared with catalysts prepared by standard wet impregnated methods has been probed using two-dimensional T1–T2 NMR correlations, H2O temperature programmed desorption (TPD) and DRIFTS. The catalysts were examined for the selective catalytic reduction of NOx using n-octane in the presence and absence of H2. Higher activities were observed for the ball milled catalysts irrespective of whether H2 was added. This higher activity is thought to be related to the increased affinity of the catalyst surface towards the hydrocarbon relative to water, following mechanochemical preparation, resulting in higher concentrations of the hydrocarbon and lower concentrations of water at the surface. DRIFTS experiments demonstrated that surface isocyanate was formed significantly quicker and had a higher surface concentration in the case of the ball milled catalyst which has been correlated with the stronger interaction of the n-octane with the surface. This increased interaction may also be the cause of the reduced activation barrier measured for this catalyst compared with the wet impregnated system. The decreased interaction of water with the surface on ball milling is thought to reduce the effect of site blocking whilst still providing a sufficiently high surface concentration of water to enable effective hydrolysis of the isocyanate to form ammonia and, thereafter, N2

Pt Nanoparticles on Beta zeolites for Catalytic Toluene Oxidation: Effect of the Hydroxyl Groups of Beta Zeolite**

Stabilisation of metal species using hydroxyl-rich dealuminated zeolites is a promising method for catalysis. However, insights into the interactions between the hydroxyl groups in zeolite and noble metals and their effects on catalysis are not yet fully understood. Herein, comparative studies were conducted using Pt catalysts supported on hydroxyl-rich dealuminated Beta (deAl-Beta) and the pristine proton-form Beta (H-Beta) for catalytic oxidation of toluene. The findings suggest that during impregnation the Pt precursor (i. e., Pt(NH3)4(NO3)2) interacted with different sites on deAl-Beta and H-Beta, leading to the formation of supported Pt nanoparticles with different physicochemical properties. In detail, for H-Beta, the Pt precursor interacted with Al-OH and isolated external Si-OH sites, yielding Pt NPs with a higher Pt0 proportion of ~71 % compared to ~57 % Pt0 on deAl-Beta. Comparatively, abundant hydroxyl groups on deAl-Beta such as silanol nest and isolated internal Si-OH stabilised highly active Pt-O species. The resulting Pt/deAl-Beta exhibited improved activity and anti-coking ability than Pt/H-Beta in catalytic toluene oxidation. For example, the temperature for 50 % toluene conversion was 193 °C for Pt/deAl-Beta vs. 232 °C for Pt/H-Beta, and the coke deposition was 1.7 % vs. 6.7 % (after the 24-h longevity test), respectively. According to the toluene-temperature programmed desorption (toluene-TPD), 1H nuclear magnetic resonance (1H NMR) relaxation and in situ diffuse reflection Fourier transform spectroscopy (in situ DRIFTS) characterisation, the enhanced performance of Pt/deAl-Beta could be ascribed to (i) the active Pt-O sites stabilised by hydroxyl groups, which interact with toluene easily for conversion, and (ii) the acid-free feature of the deAl-Beta support, which avoids the formation of coke precursors (such as benzoate species) on the catalyst surface. Findings of the work can serve as the design guidelines for making effective supported metal catalysts using zeolitic carriers

Low-field 2D NMR relaxation and DRIFTS studies of glucose isomerization in zeolite Y: new insights into adsorption effects on catalytic performance

Sn and Ga doped zeolite Y catalysts were tested for the isomerization of glucose to fructose carried out in different solvents (water, methanol and ethanol). Therein, ethanol favoured a Lewis acid site catalyzed pathway that promotes glucose isomerization to fructose, whereas methanol resulted in an equal distribution of products (mannose, fructose and alkyl fructoside). In contrast, the catalysts were totally inactive in water solvent. NMR relaxation measurements, including solvent displacement experiments, suggested that the lack of catalytic activity in water is due to the strong adsorption of this solvent within the zeolite pores blocking reactants from the Lewis acid sites active for the sugar isomerization. In comparison, ethanol adsorbs relatively more strongly than methanol, hence is retained in the pores where solvated fructose is preferentially prevented from the further reaction on Brønsted acid sites situated outside of the pore space. NMR relaxation measurements using pyridine and tetrahydrofuran (THF) and pyridine-DRIFTS measurements suggest metal doping had little effect on the overall relative acid strength of the zeolites but resulted in zeolites with increased Lewis acid strength relative to the non-doped zeolites. The results reported provide direct experimental evidence on the importance of adsorption properties of solvents within zeolites used for glucose to fructose isomerization and may serve as a starting point for a new approach towards designing and optimizing such catalytic systems

Unraveling the H-2 Promotional Effect on Palladium-Catalyzed CO Oxidation Using a Combination of Temporally and Spatially Resolved Investigations

The promotional effect of H2 on the oxidation of CO is of topical interest, and there is debate over whether this promotion is due to either thermal or chemical effects. As yet there is no definitive consensus in the literature. Combining spatially resolved mass spectrometry and X-ray absorption spectroscopy (XAS), we observe a specific environment of the active catalyst during CO oxidation, having the same specific local coordination of the Pd in both the absence and presence of H2. In combination with Temporal Analysis of Products (TAP), performed under isothermal conditions, a mechanistic insight into the promotional effect of H2 was found, providing clear evidence of nonthermal effects in the hydrogen-promoted oxidation of carbon monoxide. We have identified that H2 promotes the Langmuir–Hinshelwood mechanism, and we propose this is linked to the increased interaction of O with the Pd surface in the presence of H2. This combination of spatially resolved MS and XAS and TAP studies has provided previously unobserved insights into the nature of this promotional effect

An Investigation of the Preparation and Properties of Ag Catalysts for NOx Reduction

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