The catalytic stability of some selected bifunctional nanoporous-based catalysts in the hydroisomerisation of n-C7 and the effect of post-synthesis modification techniques

Abstract

In this work, some commercial and in-house nanoporous-based catalysts, such as USY, beta and mordenite zeolites, and mesoporous aluminosilicate molecular sieves such as MCM-48 and SBA-15, loaded with metals and acting as mono-and bimetallic bifunctional catalysts, were used for hydroisomerisation experiments in a fixedbed reactor at pressures between 1 and 15 bar and at feed space time ranging from 2.57 to 10.26 h-1 (35.14-140.6 kg s mol-1) to hydroisomerise n-heptane over a temperature range of 210-270°C. The effect of post-synthesis treatments of micro-and mesoporous catalysts was examined, regarding their activity, selectivity and stability, such as acid and steam dealumination techniques, acid leaching via a chelating agent, bimetal loading techniques, different platinum loading methods, and composite or hybrid catalyst generation. Results show that pore architecture is the most important factor affecting coke formation and deactivation in zeolite catalysts. It was found that those catalysts with high Si/Al ratios and those which had been acid-leached or steamed showed better activity, higher selectivity towards isomeric products and better time stability. Moreover, the balance between the number of metal sites and the number of acid sites played an important role in determining the activity, selectivity and stability of the bifunctional catalysts. Higher metal loading improves catalytic stability, due to a better balance and closeness of the catalytic functions. Moreover, the bimetallic catalyst improves the formation of smaller metal particles and better dispersion, which may affect selectivity and stability.

Unified kinetics of n-heptane hydroisomerisation over various Pt/zeolite catalysts

“…In the present work, n-heptane (an important constituent of heavy naphtha) was selected as a model n-alkane for studying the hydroisomerisation reaction over a zeolite-based catalyst. Various studies have been reported describing the development of a zeolite catalyst and its effect on n-heptane hydroisomerisation [1][2][3]6,[8][9][10][11][12][13][14][15][16][17][20][21][22][23][24][25][26]28,29,31,32,34,35,[40][41][42][43]. However, the kinetics of the hydroisomerisation of n-heptane over a zeolite-based catalyst have been studied by only a few [12,26,32].…”

“…Various characterisation techniques, such as inductively coupled plasma-optical emission spectroscopy (ICP-OES), X-ray diffraction (XRD), 27 Al and 29 Si MAS-solid-state nuclear magnetic resonance (NMR), pyridine adsorption-FTIR spectroscopy, ammonia-temperature programmed desorption (NH 3 -TPD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDXA) analysis, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), hydrogen chemisorption of platinum and N 2 -BET surface area analysis, were used to characterise the catalysts. A few results of catalyst characterisation are given in Table 2 while www.prkm.co.uk details regarding catalyst preparation and the results of characterisation may be found in Alotaibi et al [42] and Alotaibi et al [43]. Figure 1 illustrates the experimental setup of the pressure rig used for the n-heptane hydroisomerisation.…”

“…For each catalyst, all the experiments were carried out in the stable region of the catalyst activity and selectivity and, when not in use, the catalyst was kept under a constant flow of hydrogen. Further details of experimental setup and procedure are given in Alotaibi et al [42] and Alotaibi et al [43]. Figure 2 shows the conversion of n-heptane as a function of W/F A0 and temperature at 1 bar total pressure for the six different types of catalysts (see Table 1).…”