Isomerization of n-hexane with Pt/Ni-based catalysts supported on Al-rich zeolite Beta and correlation with acidity and oxidation state of metal crystallites

• Published in: Applied catalysis. A, General General, 2015-04, Vol.495, p.173-183
• Main Authors: Oliveira, K D, Santana, R C, Avila-Neto, C N, Cardoso, D
• Format: Article
• Language: English
• Subjects: Aluminum; Catalysis; Catalysts; Isomerization; Nickel; Reduction; Silicon dioxide; Zeolites
• ISSN: 0926-860X; 1873-3875
• DOI: 10.1016/j.apcata.2015.02.016

A fractional factorial design 2 super(5-1) was used to evaluate the effect of temperature, time, and the ratios TEAOH/SiO sub(2), Si/Al, and H sub(2)O/SiO sub(2) in crystallization of Al-rich zeolite Beta. The main effect of TEAOH/SiO sub(2) ratio was not significant. However, the Al-rich BEA structure was formed when partially substituting the tetraethylammonium cations by Na+. The activity and selectivity to bi-branched isomers in isomerization of n-hexane is directly proportional to the amount to Al atoms in the crystal lattice of BEA structure. TPD-NH sub(3) analyses showed that the improvement of such properties may be a result of the increased amount of Bransted acid sites on the zeolite surface. XANES analyses with bimetallic Pt/Ni catalysts demonstrated that, at reduction temperatures higher than 673 K, the reduction degree of Ni does not influence the activity of isomerization of n-hexane. Instead, the metal particles become more agglomerated and the activity decreases considerably. It is supposed that the rate limiting step of isomerization is the protonation of n-hexane on the Bransted acid sites of zeolites.