Hydroxyl Groups of Exceptionally High Acidity in Desilicated Zeolites Y.

The desilication of dealuminated zeolite Y in NaOH/tetrabutylammonium hydroxide mixtures produces hierarchical zeolite Y containing a micropore system as well as mesopores of significant volume and surface. IR studies evidenced that a new kind of hydroxyls was formed if desilication was realized above 318 K. This new kind of acidic hydroxyls is characterized by IR band at 3600 cm-1 . IR studies showed, that these new hydroxyls showed extremely high acidity. This was evidenced by very high frequency shifts of IR bands of OH interacting with probe molecules: CO and N2 : <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mrow><mml:mi>Δ</mml:mi> <mml:mi>ν</mml:mi></mml:mrow> <mml:mrow><mml:mi>O</mml:mi> <mml:mi>H</mml:mi> <mml:mo>·</mml:mo> <mml:mo>·</mml:mo> <mml:mo>·</mml:mo> <mml:mi>C</mml:mi> <mml:mi>O</mml:mi></mml:mrow> </mml:msub> </mml:math> =411 cm-1 and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mrow><mml:mi>Δ</mml:mi> <mml:mi>ν</mml:mi></mml:mrow> <mml:mrow><mml:mi>O</mml:mi> <mml:mi>H</mml:mi> <mml:mo>·</mml:mo> <mml:mo>·</mml:mo> <mml:mo>·</mml:mo> <mml:msub><mml:mi>N</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:mrow> </mml:msub> </mml:math> =164 cm-1 , resp. These frequency shift are the highest in all the chemistry of zeolites including very strongly acidic dealuminated mazzite and steamed zeolite USY ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mrow><mml:mi>Δ</mml:mi> <mml:mi>ν</mml:mi></mml:mrow> <mml:mrow><mml:mi>O</mml:mi> <mml:mi>H</mml:mi> <mml:mo>·</mml:mo> <mml:mo>·</mml:mo> <mml:mo>·</mml:mo> <mml:mi>C</mml:mi> <mml:mi>O</mml:mi></mml:mrow> </mml:msub> </mml:math> =ca. 380 cm-1 ) indicating that 3600 cm-1 hydroxyls are the most acidic in all the zeolites.