Artificial zeolites
Zeolites are industrially important materials possessing high Bronsted acidity and shape-selectivity. However, their inherently small pores restrict application for catalytic conversion of bulky molecules. A method of synthesis of ‘artificial’ zeolites. The artificial zeolites have well-tailored Bronsted and Lewis acid sites prepared on mesostructured silica to circumvent this limitation. This novel approach utilizes atomic layer deposition to tailor both porosity and acid speciation, providing exquisite control over catalytic behavior and enabling systematic studies.
1. A method of increasing Bronsted acidity creating an artificial zeolite, comprising:
depositing aluminum on a silica substrate by atomic layer deposition (ALD), forming amorphous silica-alumina on a porous amorphous silica substrate, thereby forming a plurality of Lewis acid sites;
depositing, on the porous amorphous silica substrate, a single atomic layer of a material having a silicon-oxygen species by atomic layer deposition comprising a trimethylsilanol (TMSiOH) exposure followed by an ozone exposure, wherein the depositing is repeated 0-7 times to form 1-8 atomic layers of the silicon-oxygen species; and
forming a plurality of silanol functional groups on the porous amorphous silica substrate, thereby converting a portion of the Lewis acid sites into exposed surface Bronsted acid site.
2. The method of claim 1 , wherein for a portion of the plurality of silanol functional groups, further comprising forming a bridge with an adjacent aluminum atom.
3. The method of claim 1 , wherein the deposition of the aluminum-containing material comprises a single exposure to trimethyl aluminum (TMA).
4. The method of claim 3 , wherein the deposition of the aluminum-containing material further comprises a water exposure following the single TMA exposure, followed by a purge and then the TMSiOH exposure.
5. The method of claim 4 , wherein the deposition of the silicon-oxygen material comprises between 3 and 30 TMSiOH ALD cycles.
6. The method of claim 5 , wherein after forming the plurality of Bronsted acid sites, the ratio of Lewis acid sites to Bronsted acid sites is 40:60.
7. The method of claim 1 , wherein a plurality of Bronsted acid sites are added to the amorphous silica-alumina.
8. A method of creating an artificial zeolite, comprising:
a first ALD deposition forming a silica-alumina layer on a substrate, the first ALD deposition comprising:
an exposure to TMA; and
an exposure to an oxiding precursor; and
a second ALD deposition forming a Bronsted Acid site, the second ALD deposition comprising:
an exposure to a silanol precursor consisting of trimethyl silanol; and
an exposure to ozone;
wherein the second ALD deposition comprises reacting the silanol precursor with either a trimethyl aluminum group or an aluminum hydroxide group of the silica alumina layer.
9. A method of increasing Bronsted acidity creating an artificial zeolite, comprising:
depositing aluminum on a silica substrate by atomic layer deposition, forming amorphous silica-alumina on a porous amorphous silica substrate thereby forming a plurality of Lewis acid sites;
depositing, on the porous amorphous silica, a single atomic layer of a material having a silicon-oxygen species by atomic layer deposition comprising a trimethylsilanol (TMSiOH) exposure followed by an ozone exposure; wherein the depositing is repeated 0-7 times to form 1-8 atomic layers of the silicon-oxygen species; and
forming, by removal of methyl groups, a plurality of silanol functional groups on the porous amorphous silica substrate, thereby converting a portion of the Lewis acid sites into exposed surface Bronsted acid site.