n-Heptane hydroconversion over nickel-loaded aluminum- and/or boron-containing BEA zeolites prepared by recrystallization of magadiite varieties

Abstract

Phase-pure [Al]BEA and [Al,B]BEA zeolites, prepared by solid-state recrystallization of synthetic aluminum-containing magadiites and conventionally synthesized [B]BEA, were tested, after ion exchange with nickel, as bifunctional catalysts for hydroconversion of n-heptane. The reducibility of nickel ions incorporated into BEA zeolites by ion exchange was investigated by temperature-programmed reduction (TPR). The acidity of the samples was characterized with strong (pyridine (Py), ammonia (NH 3 )) and weak (nitrogen) bases. The adsorbed bases were studied by transmission FT-IR (Py), diffuse reflectance infrared Fourier-transform (DRIFT) spectroscopy (N 2 ), and temperatureprogrammed ammonia evolution (TPAE, NH 3 ). Over Ni/H-[B]BEA the reactants were completely converted via fast hydrogenolysis, whereas this reaction pathway plays only a negligible role in the hydroconversion over Ni/H-[Al]BEA and Ni/H-[Al,B]BEA zeolites. Boron-containing BEA zeolites were less active catalysts than the boron-free catalyst in the principal unimolecular hydroconversion reactions. However, incorporation of boron into the framework of BEA zeolite results in a considerable selectivity shift towards isomerization. Results suggest that the acid strength of bridged hydroxyls, probed with weak (N 2 ) and strong basis (pyridine), was found to be similar in the boron-free and boroncontaining BEA samples. The decrease in the isomerization rate and the increase of the apparent activation energy upon incorporation of boron may be attributed to the decrease in the heat of n-heptane adsorption.

n-Heptane hydroconversion over sulfated-zirconia-supported molybdenum carbide catalysts

“…n-Heptane was selected due to the challenges in obtaining a catalyst which avoids excessive cracking [51]. One of the major issues related to the use of sulfated zirconia catalyst is that deactivation often occurs after a few minutes of reaction.…”

“…Working at very low temperature (\423 K) will increase the selectivity to iso-heptanes, because they are thermodynamically favourable and stable at such low temperature, but it has disadvantage of producing low yield. Mihályi et al [51] have suggested that hydrocracking is not negligible at high conversions level, but high conversion can only be achieved either at high temperature or at low WHSV. The observation is consistent with the data obtained in this research.…”

Reactivity and applications of layered silicates and layered double hydroxides

“…In fact, high-silica mordenite (Si/Al = 14-23) (MOR) has now been prepared by hydrothermal condensation of the RUB-18 using Al[OCH(CH 3 ) 2 ] 3 or Na 2 Al 2 O 4 as the aluminium sources. 71 Additionally, several known zeolites (MFI, 72 MEL, 72 FER, 73,74 Al-and B-BEA, 75,76 silicalite-1, 77 Mn-silicalite-1, 43 Co-silicalite-1, 78 Co-MFI and Co-BEA, 44 MOR, [79][80][81] OFF 82,83 ) have been synthesized using the layered silicate magadiite as the precursor and respective structure directing agents (Table 3). In recent years, zeolites such as MFI-type nanosheets 84 and omega (MAZ) 85 have been synthesized using magadiite as the precursor under hydrothermal and solvothermal conditions, respectively.…”

Transformation of ethylbenzene–m-xylene mixture on zeolites with different structures

“…The NH 4 + -ion exchange capacity (IEC) of the samples were characterized by TPAE (Temperature-Programmed Ammonia Evolution) measurements described elsewhere [26] and presented in Table 1. About 300 mg of samples were heated from 423 to 823 K at a rate of Spectra were normalized to wafer thickness of 5 mg/cm 2 .…”