Sohair M. Abdel-Hamid

Catalytic para-xylene maximization II – alkylation of toluene with methanol on platinum loaded H-ZSM-5 zeolite catalysts prepared via different routes

Abstract Two series of catalysts, A and B, each containing 0.2%, 0.4%, and 0.6% Pt on H-ZSM-5 zeolite, were prepared via two different procedures; catalysts of series A were prepared via impregnating H-ZSM-5 with the Pt precursor (H 2 PtCl 6 ) solution, whereas those of series B were prepared via impregnating NH 4 -ZSM-5 zeolite with the Pt precursor solution followed by deammoniation to the Pt/H-ZSM-5 forms. The prepared catalysts were examined for toluene alkylation with methanol in a flow reactor under atmospheric conditions using H 2 gas carrier. The catalysts were characterized for acidity magnitude and strength via temperature programmed desorption of ammonia (TPD) and for Pt dispersion in the zeolite via H 2 chemisorption. Correlation of the catalysts characteristics with their reactivities for toluene conversion, xylenes production, trimethylbenzenes formation and xylene isomers in product relative to their thermodynamic equilibrium values were carried out.

Impregnation design for preparing bimetallic catalysts

Abstract The data show how two metal precursors, possessing equal rates of adsorptionon a λ-alumina support, be homogeously dispersed through adding a proper additive (HCl) for preparing bimetallic catalysts, whereas two metal precursors, possessing different adsorption rates, could not be homogeneously dispersed or distributed in the support while using this additive. Chloroplatinic and chloroiridic acids are examples of the first type whereby PtIr-containing catalysts are prepared. Chloroplatinic acid and ammonium paratungstate are examples of the second type whereby PtW-containing catalysts are prepared. For preparing PtIr-containing catalysts a single impregnation of the two precursors from one solution is thus possible, whereas for preparing PtW-containing catalysts, two impregnations from two separate precursor solutions are to be carried out.

Isomerization of xylene isomers on a PtRe-H-mordenite catalyst

Abstract The isomerization of three xylene isomers was carried out on a catalyst containing 0.35 wt.-% platinum plus 0.35 wt.-% rhenium on hydrogen mordenite in a pulse catalytic microreactor positioned at the inlet of a gas chromatograph. Reactant injections were carried out at temperatures between 300 and 400 °C with hydrogen gas flow at atmospheric pressure. High ratios of para-xylene in the product xylene isomers mixture relative to the corresponding thermodynamic equilibrium values (2.9–3.5) were obtained, whereas the ratios of meta-xylene (0.33–0.69 ) were low and those of ortho-xylene were very low (0.093–0.18). However, relatively high dealkylation products (toluene and benzene) were obtained at higher temperatures. Disproportionation products (trimethylbenzenes) were not detected in the reaction products.

Hydroisomerization of n-Hexane Using Unloaded and Low-Platinum-Loaded H-ZSM-5 and H-MOR Catalysts

Abstract The applicability for investing and comparing two zeolites (H-ZSM-5 and H-MOR) as supports for low-platinum (less expensive) catalysts used principally for hydroisomerization of n-paraffins in light petroleum naphtha is investigated using n-hexane as a model n-paraffin feed at temperatures of 250°C–500°C in a flow-type reactor with a hydrogen flow of 20 cm3 min−1 at atmospheric pressure. H-ZSM-5 zeolite acquires higher density of strong acid sites, which are still somewhat weaker than the respective sites in H-MOR. These milder sites in H-ZSM-5 zeolite enhanced hydroisomerization and dehydrocyclization but suppressed hydrocracking after incorporating 0.15% Pt. Hydrochlorination (HCl) and hydrofluorination (HF) of 0.15% Pt/H-ZSM-5 were carried out to modify its acidity and Pt dispersion with the goal of maximizing n-hexane hydroisomerization. The HCl treatment seems to have significantly approached the requirement for optimum catalytic bifunctionality, whereas HF treatment appears mostly deteriorative.

Direct Conversion of Natural Gas to Petrochemicals Using Monofunctional Mo/SiO2 and H-ZSM-5 Zeolite Catalysts and Bifunctional Mo/H-ZSM-5 Zeolite Catalyst

Abstract The components of the standard catalyst globally used for natural gas direct conversion (6% Mo/H-ZSM-5) have been separately prepared and examined to represent: (a) monofunctional metallic component (6% Mo/SiO2) and (b) acidic component (H-ZSM-5 zeolite) to numerically investigate the extent of activity of each catalytic component in comparison to the activity of the standard catalyst in a fixed-bed flow-type reactor. The temperature and gas hourly space velocity are 700°C and 1500 mLg−1 h −1, respectively, which are very close to those used in the industrial gas conversion reactions. Time on stream up to 240 min was examined. The gaseous products were ethylene, propylene, and hydrogen, whereas the liquid products were benzene, toluene, and naphthalene. Carbon was also produced as deposited particles on the catalyst.

Nanosized Platinum-Loaded H-ZSM-5 Zeolite Catalysts for n-Hexane Hydroconversion

Abstract A series of nanosized platinum-containing catalysts was successfully loaded on/in zeolite H-ZSM-5 via exchanging the zeolitic proton with platinum from Pt tetramine dichloride complex. Another series of Pt/H-ZSM-5 catalysts was prepared via wet impregnation of H2PtCl6 solution for comparison. The latter series was found to produce lower Pt dispersion. Pt dispersion was determined by H2 chemisorption. Catalyst characterization via ammonia temperature-programmed desorption (TPD), temperature-programmed reduction (TPR), and transmission electron microscopy (TEM) was examined for all catalysts and showed large differences in particle sizes. The data on n-hexane reactions of the catalysts of both series confirmed the formation of Pt nanoparticles in the exchanged catalysts. The relatively lower density and strength of acid sites acquired by Pt-exchanged catalysts contributed to this difference; stronger acid sites in the impregnated catalysts are in favor of hydrocracking reactions, which inhibit isomerization selectivity.

Hydrohalogenation of Platinum–Palladium/H-ZSM-5 Catalysts for n-Hexane Hydroconversion

Catalysts containing 0.3%Pt-, 0.3%Pd-, and 0.3%Pt-0.3%Pd-/H-ZSM-5 were prepared and modified via hydrochlorination or hydrofluorination and tested for n-hexane hydroconversion throughout a reaction temperature range of 250–500°C. Bifunctionality parameters of the current catalysts were characterized via acid site strength distribution by NH3-temperature programmed desorption, metal(s) component dispersion by H2 chemisorption, and temperature programmed reduction. Hydrochlorination was found to leach less structural zeolitic Al in the catalyst than hydrofluorination. HCl modification improved n-hexane hydroisomerization activity, whereas HF treatment was deteriorative via causing pore diffusion restriction by excessively formed debris. Acid sites density and strength were higher on hydrofluorination than on hydrochlorination. Surface area and metals dispersion were higher for hydrochlorinated catalyst but lower for the hydrofluorinated one. Maximum isohexanes production (70%) was realized on hydrochlorinated catalyst at 350°C with 100% selectivity. Crystal unit cell d-spacing, obtained by XRD, was smaller by hydrofluorination than by hydrochlorination, whereas such d-spacing was increased through incorporating Pt and increased more via Pd addition during preparation.

Comparative Evaluation of Catalysts Containing 0.35% Pt Supported on H-BEA Zeolite Dealuminated via EDTA, HCl Leaching, or Hydrothermally With Steam

Abstract H-BEA was steamed at 500°C for 2 hr and then loaded with Pt to produce 0.35% Pt/St-H-BEA catalyst. Also, H-BEA was dealuminated with ethylenediamine tetraacetic acid (EDTA) and then loaded with Pt to produce 0.35% Pt/EDTA-H-BEA catalyst. Finally, H-BEA was dealuminated via HCl leaching followed by Pt loading to produce 0.35%Pt/HCl-H-BEA catalyst. These catalysts were reduced under H2 flow at 500°C to give Pt metal. All catalysts were tested at 250°C–450°C for n-hexane hydroconversion. Maximum hydroisomerization of n-hexane was attained (75.1%) on 0.35% Pt/EDTA-H-BEA and 0.35% Pt/HCl-H-BEA catalysts but at 275°C on the former catalyst and at 300°C on the latter. At this temperature, n-hexane hydrocracking is only 1.2%. The hexane isomers selectivity on both catalysts was >99%. For the 0.35% Pt/St H-BEA catalyst, isohexanes yield and selectivity were lower than the above-mentioned catalysts. The catalyst of choice is 0.35% Pt/EDTA-H-BEA for its economic application at 275°C.

High Yields of LPG Via n-Hexane Hydrocracking Using Unloaded Acidic Zeolite Catalysts

This work includes investigating the hydrocracking of n-hexane, as a low-octane naphtha component to high-octane gaseous motor fuel (LPG) in a pulse flow atmospheric microreactor using untreated and steam-treated H-MOR, H-BEA, or H-ZSM-5 zeolite catalysts. All zeolites were metal-free and their bifunctionality depended only on the Brønsted zeolitic acid sites. The temperature programmed desorption analysis was performed to compare the weak and strong acid sites in the current catalysts. The catalytic activities of the catalysts were found to correlate well with their acid strengths. The most active catalyst was St-H-MOR, which acquired the strongest acid sites and highest densities. On this catalyst, 92.1% LPG was produced at 350°C, whereas on the un-steamed one (H-MOR), the LPG yield amounted to 88.0% at the same temperature. Maximum LPG production on H-BEA acquired 84.6% at 400°C, whereas on St-H-BEA, it acquired a close yield (85.7%). Zeolites H-ZSM-5 and St-H-ZSM-5 acquire very low catalytic activities mainly due to their narrow pore structure, as well as due to their partial pore filling by Al debris in case of St-H-ZSM-5.

Reactions of Cyclohexane on Platinum, Palladium, or Iridium-loaded H-ZSM-5 Zeolite Hydrohalogenated Catalysts

Abstract The catalytic hydroconversion of cyclohexane using catalysts containing H-ZSM-5 zeolite loaded with 0.35 wt% platinum, palladium, or iridium was studied in a pulse-type microreactor/GC system at atmospheric pressure. These catalysts were also either doped with 3.0% of HCl or HF. The activities of these catalysts and the distribution of the products formed were found to depend on the dispersion of the metallic component as well as on the acidity, acid sites number, and strength in the catalysts. TPD of ammonia and hydrogen chemisorption were applied to evaluate acid site strength distribution and metals dispersion, respectively, in the catalysts. In case of the Pt- and Pd-containing catalysts, hydrochlorination enhanced the isomerization and dehydrogenation activities and selectivities of cyclohexane, but decreased its hydrocracking activity. However, catalyst hydrofluorination resulted in the reverse effects. Nevertheless, for the Ir-loaded catalyst, both hydrohalogenation treatments decreased the isomerization and dehydrogenation of cyclohexane. The Ir/H-ZSM-5 catalyst exhibited higher hydrogenolysis activities than did those acquired by the Pt- and Pd-containing catalysts.