AFX Zeolite (Johnson Matthey)

CATEGORY: ZEOLITES 
AFX Zeolite (Johnson Matthey)
United States Patent Application 20160137518
RIVAS-CARDONA; Alejandra ;   et al.   May 19, 2016
Applicant: Johnson Matthey Public Limited Company
Abstract

Provided is a novel form of AFX zeolite, a novel synthesis technique for producing pure phase AFX zeolite, a catalyst comprising the AFX zeolite in combination with a metal, and methods of using the same.
BACKGROUND
[0001] 1. Field of Invention
[0002] The present invention relates to method for synthesizing a zeolite and to the use of such zeolites as catalysts for treating combustion exhaust gas.
[0003] 2. Description of Related Art
[0004] Zeolites are molecular sieves having unique lattice frameworks constructed of alumina and silica cages. The Internal Zeolite Association (IZA) assigns each unique framework type a three-letter code, such as MOR, CHA, or BEA.
[0005] Synthesis of zeolite crystals typically involves reacting alumina and silica in the presence of an organic template (also referred to as a structure directing agent or SDA) at elevated temperatures for several days. During crystallization, the alumina and silica co-join to form a crystalline structure around the SDA. The reactants, reaction conditions, and the species of SDA all impact which type or types of framework that are synthesized. When sufficient crystallization has occurred, the crystals are removed from the mother liquor and dried. After the crystals are separated from the mother liquor, the organic SDA is thermally degraded and removed from the crystalline structure, thus leaving a porous molecular sieve.
[0006] Zeolites are useful as catalyst for various industrial processes, such as selectively reducing NO.sub.x in combustion exhaust gases. Several zeolites, such as zeolite Beta and ZSM-5, have been identified as being particularly useful for these types of applications. A zeolite having an AFX framework (referred to herein as AFX zeolites) has been identified as being useful for hydrocarbon cracking and reforming.
[0007] Conventional AFX zeolite synthesis techniques yield mixed phase products--that is, zeolites having two or more framework types. Mixed phase zeolites are often less desirable than pure phase zeolites for catalytic reactions.
SUMMARY OF THE INVENTION
[0008] Applicants have discovered a novel zeolite synthesis technique and a novel form of AFX zeolite. In particular, the AFX zeolite has a silica-to-alumina ratio and crystalline size that is particularly useful as a catalyst for selective catalytic reduction (SCR) of NO.sub.x in exhaust gas from lean burn engines.
[0009] Accordingly, provided is an aluminosilicate zeolite comprising at least about 90% phase pure AFX framework, a silica-to-alumina ratio of about 12-32, and preferably a mean crystal size of about 0.5-7 .mu.m.
[0010] Also provided is a method for making an aluminosilicate zeolite having an AFX framework comprising the step of reacting a synthesis gel comprising a silica source, an alumina source selected from ammonium-form zeolites and/or hydrogen-form zeolites, and a structured directing agent at a temperature of at least 100.degree. C. until crystals of AFX zeolite form.
[0011] In addition, provided is a catalyst for treating an exhaust gas comprising a pure-phase aluminosilicate AFX zeolite loaded with a metal selected from V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Rh, Pd, Ag, W, Re, Os, Ir, Pt, and Au.
[0012] Also provided is a method for using such a catalyst to treat an exhaust gas, for example by selectively reducing NO.sub.x, by storing NO.sub.x, or by oxidizing one or more of CO, hydrocarbons, and NH.sub.3. Such catalyst are preferably supported on a wall-flow filter or a honeycomb flow-through support.
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