Synthesis and characterization of Al-magadiite and its catalytic behavior in 1,4-pentanediol dehydration

Abstract

Two layered aluminosilicate samples having magadiite structure and different Al-contents were prepared by conventional hydrothermal synthesis method. The samples were characterized by XRD, N2 adsorption isotherms, temperature-programmed ammonia evolution (TPAE), and 27Al MAS NMR spectroscopy. The acidity of the samples was characterized by the FT-IR spectra of adsorbed pyridine (Py). The specific surface area (SSA) of the crystalline samples was found to depend on the Al-content of the synthesis gel. The sample of low and high Si to Al ratio (Si/Al = 19 and 35) had SSA of 61 and 260 m2/g, respectively. 27Al MAS NMR spectra of the samples indicated tetra-coordinated Al, incorporated into Q3 and/or Q4 framework sites of the aluminosilicate layer. Aluminum in Q4 sites generates bridged hydroxyls (Si–OH–Al). These hydroxyls are strong Bronsted acid sites. Bases, like Py and ammonia, are bound to these sites strongly in protonated form. There are three-coordinated Al atoms in the Q3 sites. In dehydrated samples, these sites have Lewis-acidity. These acid sites, however, are only partially accessible to Py. Acid sites were also characterized in the reaction of 1,4-pentanediol (1,4-PD) dehydration. The acidity and catalytic behavior of the magadiite samples were compared to the corresponding properties of zeolite H-ZSM-5 (Si/Al = 20) and commercial γ-Al2O3.