Hydroisomerisation of n-hexane over bimetallic bifunctional silicoaluminophosphate based molecular sieves

Silicoaluminophosphate molecular sieves SAPO-5 and SAPO-11 were synthesised hydrothermally and their purity and structure were checked by X-ray diffraction (XRD). The calcined SAPOs were impregnated with 0.2 wt.% Pt and varying amount (0, 0.2,0.4 and 0.6 wt.%) of Ni and reduced in hydrogen atmosphere. The TEM analysis shows that the average particle size of the metal particles increases with increase of Ni loading. Acidity by TPD of ammonia and pyridine adsorbed FT-IR spectra studies show that the increasing addition of Ni decreases the total acidity of the catalysts. The Ni-Pt/SAPO-5 and Ni-Pt/SAPO-11 catalysts were subjected to n-hexane hydroisomerisation in hydrogen atmosphere and found that Ni addition up to 0.4 wt.% over 0.2 wt.% Pt loaded SAPO-5 and SAPO-11 increases the n-hexane conversion, isomerisation selectivity, dibranched isomers selectivity and sustainability of the catalyst. Further, Ni addition leads to a fall in activity of the catalysts. The activity of 0.2 wt.% Pt and 0.4 wt.% Ni/SAPOs in n-hexane hydroisomerisation was compared with 0.2 wt.% Pt and 0.4 wt.% Pd/SAPOs and found that Pt-Pd/SAPOs show higher activity and isomerisation selectivity than Pt-Ni/SAPOs. Further, SAPO-5 based catalysts always show higher activity with lesser isomerisation selectivity than SAPO-11 based catalysts. (C) 2002 Elsevier Science B.V. All rights reserved.