resumo
MCM-48 aluminosilicates with different aluminium contents were synthesised by a room temperature procedure using tetraethoxy-silane and aluminium sulfate, isopropoxide or tert-butoxide as metal sources. The samples were characterised by X-ray diffraction, nitrogen adsorption at 77 K, and (27)Al MAS NMR and the catalytic activity tested in the reaction of l-butene double bond position isomerisation. The influence of the synthesis time and calcination conditions, such as heating rate and time at final temperature, on the structural and catalytic properties of the materials was also evaluated. Aluminium isopropoxide and sulfate allowed the preparation of well structured Al-MCM-48 materials, with high specific pore volume and uniform pore size, and with the majority of the aluminium incorporated in tetracoordinated environment after calcination, at least down to Si/Al of 15. The highest initial conversions were found for samples with Si/Al = 20 and 30 prepared With aluminium isopropoxide and calcined using a heating rate of 3 K min(-1) with those of samples prepared with aluminium sulfate being slightly lower. Al-MCM-48 materials with high specific pore volume and uniform size were also synthesised using aluminium tert-butoxide, but the materials were less well ordered, presented a higher proportion of hexa-and pentacoordinated Al species and exhibited lower initial conversions, independently of the synthesis time or calcination conditions tested. It is concluded that aluminium isopropoxide and sulfate are more adequate metal Sources than aluminium tert-butoxide to prepare Al-MCM-48 catalysts by this room temperature method and a calcination heating rate of 3 K min(-1) instead of I K min-1 produces more effectively active catalysts. (C) 2008 Elsevier Inc. All rights reserved.
palavras-chave
MESOPOROUS MOLECULAR-SIEVES; ETHYLENIC HYDROCARBONS; MCM-48 MATERIALS; ACIDITY; ISOMERIZATION; STABILITY; ALKYLATION; BEHAVIOR; SITES; WATER
categoria
Chemistry; Science & Technology - Other Topics; Materials Science
autores
Russo, PA; Carrott, MMLR; Carrott, PJM; Lopes, JM; Ribeiro, FR; Rocha, J
nossos autores
João Rocha
Prof. Catedrático
Patrícia Alexandra Ferreira Russo
Bolseiro de pós-Doutoramentoagradecimentos
This work was financially supported by the Fundacao para a Ciencia e a Tecnologia (FCT, Portugal) and the Fundo Europeu para o Dcsenvolvimento Regional (FEDER) (Project No. POCTI/CTM/45859/2002). P.A.R. thanks FCT for PhD Grant No. SFRH/BD/17713/2004.