Abstract
NiO(8 %)/Ni,H-ZSM-5 + Al2O3 (1:1) catalysts differing in metal-support interactions, which influenced the metal-to-acid ratios, were examined. The interactions were changed by modifying the method of zeolite and aluminium hydroxide combining and the method of Ni incorporation. The catalysts were characterised by ICP, XRD, N2 sorption, SEM, TEM, NH3-TPD, Py-IR, TPR, H2 chemisorption and XPS. The effect of metal-support interactions was determined during n-C6 conversion in a continuous system at H2:CH = 7:1 Nm3/m3, 0.1 MPa and LHSV = 1 h−1. It was found that over the catalysts with weaker Ni–alumina interactions (n Ni_a/n, 3.2 × 10−2 and 4.8 × 10−2), selectivity to isomerisation products was by 10–35 % higher, and selectivity to high boiling hydrocarbons by 10–30 % lower than over the catalysts with stronger Ni-support interactions (n Ni_a/n, 1.2 × 10−2 and 1.8 × 10−2).
Highlights
Interactions between metal and oxide support affect such physicochemical properties of the catalyst as dispersion, size and metal crystallite distribution or acidity
It was found that over the catalysts with weaker Ni–alumina interactions, selectivity to isomerisation products was by 10–35 % higher, and selectivity to high boiling hydrocarbons by 10–30 % lower than over the catalysts with stronger Ni-support interactions
Regardless of the method used for combining zeolite and alumina or nickel incorporation, metal-support interactions in NiO(8 %)/ZSM-5 ? Al2O3(1:1) catalysts are strong
Summary
Interactions between metal and oxide support affect such physicochemical properties of the catalyst as dispersion, size and metal crystallite distribution or acidity. When preparing catalysts with an active metal content higher than 10–20 wt%, preference is given to the precipitation method [5]. When catalysts of a lower active metal content are prepared, it is conventional to use the impregnation method. Since impregnation is concomitant with the adsorption of the metal precursor, knowledge of the pH value at which the support surface is neutral point of zero charge (PZC) becomes indispensable. When the pH of the solution is higher than the PZC of the support, the surface of the support is negatively charged and has the ability to adsorb cations. With a pH value lower than that of PZC, the support surface has a positive charge and adsorbs anions [8,9,10,11]
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