Boron-containing molecular sieve CHA
A boron-containing molecular sieve having the CHA crystal structure and comprising (1) silicon oxide and (2) boron oxide or a combination of boron oxide and aluminum oxide, iron oxide, titanium oxide, gallium oxide and mixtures thereof is prepared using a quaternary ammonium cation derived from 1-adamantamine, 3-quinuclidinol or 2-exo-aminonorbornane as structure directing agent. The molecular sieve can be used for gas separation or in catalysts to prepare methylamine or dimethylamine, to convert oxygenates (e.g., methanol) to light olefins, or for the reduction of oxides of nitrogen n a gas stream (e.g., automotive exhaust).
1. A method for preparing a boron-containing molecular sieve having the CHA crystal structure and comprising (1) silicon oxide and (2) boron oxide or a combination of boron oxide and aluminum oxide, iron oxide, titanium oxide, gallium oxide and mixtures thereof, said method comprising:
A. forming an aqueous reaction mixture comprising a composition in terms of mole ratios falling within the following ranges:
YO 2 /W a O b
>2–2,000
OH—/YO 2
0.2–0.45
Q/YO 2
0.2–0.45
M 2/n O/YO 2
0–0.25
H 2 O/YO 2
22–80
wherein Y is silicon, W is boron or a combination of boron and aluminum iron, titanium, gallium and mixtures thereof; a is 1 or 2 and b is 2 when a is 1 or b is 3 when a is 2; M is an alkali metal or alkaline earth metal, n is the valence of M, Q is a quaternary ammonium cation delved from 1-adamantamine, 3-quinuclidinol or 2-exo-aminonorbornane and wherein the aqueous reaction mixture does not contain fluorine; and
B. maintaining said aqueous mixture under sufficient crystallization conditions until crystals are formed.
2. The method of claim 1 wherein oxide (2) is more than 50% boron oxide on a molar basis.
3. The method of claim 1 wherein Y is silicon and W is boron.
4. A boron-containing molecular sieve having the CHA crystal structure and having a composition, as-synthesized and in the anhydrous state, in terms of mole ratios of oxides as follows:
YO 2 /W c O d
20–2,000
M 2/n O/YO 2
0–0.03
Q/YO 2
0.02–0.05
wherein Y is silicon, , W is boron or a combination of boron and aluminum, iron, titanium, gallium and mixtures thereof; c is 1 or 2; d is 2 when c is 1 or d is 3 or 5 when c is 2; M is an alkali metal cation, alkaline earth metal cation or mixtures thereof; n is the valence of M (i.e., 1 or 2); Q is a quaternary ammonium cation derived from 1-adamantamine, 3-quinuclidinol or 2-exo-aminonorbornane and wherein the as-synthesized molecular sieve does not contain fluorine.
5. The molecular sieve of claim 4 wherein oxide (2) is more than 50% boron oxide on a molar basis.
6. The as-synthesized molecular sieve of claim 4 wherein Y is silicon and W is boron.