Alkane conversion over Pd/SAPO molecular sieves: influence of acidity, metal concentration and structure

• Published in: Catalysis today Vol. 65; no. 2; pp. 171 - 177
• Main Authors: Höchtl, M, Jentys, A, Vinek, H
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Amsterdam Elsevier B.V 20.02.2001; Elsevier Science
• Subjects: Acid site concentration; Alkane isomerization; Catalysis; Catalytic reactions; Chemistry; Exact sciences and technology; General and physical chemistry; Metal loading; SAPO-11; SAPO-5; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Acid site concentration; Metal loading; SAPO-11; SAPO-5; Alkane isomerization; Catalytic reaction; Hydrocarbon; Isomerization; Acidic site; Transition metal; Palladium; Experimental study; Heptane; Supported catalyst; Molecular sieve; Heterogeneous catalysis; Preparation; Alkane; Concentration effect; Platinoid; Catalyst activity
• ISSN: 0920-5861; 1873-4308
• DOI: 10.1016/S0920-5861(00)00581-2

The activity and selectivity for the isomerization of heptanes over Pd-loaded SAPO molecular sieves with AEL and AFI structure were investigated. By synthesis of the AEL molecular sieves from Al-isopropoxide, the acid site concentration could be controlled by the amount of silicon in the synthesis gel. The resulting concentration of SiAl–OH groups ranged from 0.07 to 0.3 mmol/g, exhibiting the same acid strength, independent from the acid site concentration. Catalysts were impregnated with 0.1–2 wt.% Pd. The activity increased with increasing Pd content up to a Pd to acid site ratio of 0.02–0.03. Above this value, the metal loading did not influence the activity. A further enhancement of the activity was possible by increasing the number of SiAl–OH acid sites. The selectivity to isomerization was constant for the catalysts with an acid site concentration >0.19 mmol/g. The catalysts synthesized from Al-isopropoxide showed a lower activity compared to the catalysts synthesized from aluminum oxide, probably due to diffusional restrictions caused by the formation of polycrystalline agglomerates.