A ZEOLITE COMPOSITE AND APPLICATIONS THEREOF
FIELD OF THE INVENTION
The invention relates to a zeolite composite, such as a titanium chabazite (CHA) or a titanium AEI. The invention further relates to a catalyst article comprising the composite and a method for the treatment of an exhaust gas which comprises contacting an exhaust gas with a catalyst article comprising the composite.
BACKGROUND OF THE INVENTION
Zeolites are crystalline or quasi-crystalline aluminosilicates constructed of repeating TO4 tetrahedral units with T being most commonly Si, Al or P (or combinations of tetrahedral units). These units are linked together to form frameworks having regular cavities and/or channels of molecular dimensions within the crystal. Numerous types of synthetic zeolites have been synthesized and each has a unique framework based on the specific arrangement its tetrahedral units. By convention, each topological type is assigned a unique three-letter code (e.g., “CHA” or “AEI”) by the International Zeolite Association (IZA).
NH3-SCR is the most effective technique for NOx abatement in lean-burning engine exhaust after-treatment. In this regard, Cu-SSZ-13 has been commercialized as an NH3-SCR catalyst for its significant advantages of excellent catalytic performance and hydrothermal stability. SSZ-13 (framework type code CHA) is a high-silica aluminosilicate zeolite and Cu- SSZ-13 refers to the copper loaded zeolite, commonly prepared by incipient wetness or ionexchange.
Wang et al. (Ind. Eng. Chem. Res. 2022, 61, 15066-15075) describe the doping effect of transition metals (Fe, Ti, Mn and Ce) on the structure and catalytic performance of Cu-SSZ- 13 zeolite catalysts for the NH3-SCR reaction. Transition metal doping by ion exchange was found to lead to substitution of the Cu species by dopants at ion-exchange sites, aggravating the possibility of zeolite framework structure collapse, thus leading to relatively poor hydrothermal stability along with lower low temperature performance and inferior tolerance against sulfur poisoning.
Zhang et al. (Microporous and Mesoporous Materials 255 (2018) 61-68) describe enhanced photocatalytic activity of a TiCE/zeolite composite for abatement of pollutants. The characterization results illustrated that anatase TiCE nanoparticles were stabilized on the surface of the zeolite support. Yue Ma et al., (React. Chem. Eng., 2022, 7, 2121) describes the combination of Cu- SSZ-13 and TiCh nanoparticles by a simple impregnation method.
Wan, J., Chen, J., Shi, Y. et al. (Catal Surv Asia 26, 346-357 (2022)) describe a series of Ti/Cu-SSZ-13 zeolite catalysts. The catalysts have variable Ti contents and are prepared via an in-situ one-pot synthesizing strategy.
US9,889,437 describes an SCR catalyst comprising a zeolite with a framework material of silicon and aluminum atoms, wherein a fraction of the silicon atoms are isomorphously substituted with Ti.
There remains a need in the art of for alternative methods for the treatment of exhaust gas and new catalytic articles, especially those which exhibit improved NOX conversion and selectivity (e.g., at low temperature, either fresh or aged) for use in NOX abatement catalysts in the selective catalytic reduction of NOX.
SUMMARY OF THE INVENTION
One aspect of the invention is directed to a composite for treating a NOx-containing exhaust gas, the composite comprising a copper-substituted zeolite and one or more of Ti, Zr, Y, Ce, Er and Nd.
Another aspect of the invention is a catalyst article for the treatment of an exhaust gas, the catalyst article comprising the composite as described herein.
Another aspect of the invention is directed to a method for the treatment of an exhaust gas, the method comprising contacting an exhaust gas with the catalyst article described herein.
Another aspect of the invention is directed to a method for the manufacture of a composite comprising a zeolite and one or more of Ti, Zr, Y, Ce, Er and Nd, the method comprising:
(i) providing a composition comprising a zeolite and an inorganic compound of one or more of Ti, Zr, Y, Ce, Er and Nd, the composition having a pH of less than 7; and
(ii) adding a base to the composition, thereby increasing the pH of the composition and yielding the composite; wherein the zeolite has a CHA or an AEI framework. Another aspect of the invention relates to a composite producible by the method above, the composite comprising a (bare) zeolite and one or more of Ti, Zr, Y, Ce, Er and Nd (preferably titanium), wherein the zeolite has a CHA or AEI framework.
Another aspect of the invention is directed to intermediates produced during the methods of the invention.
Another aspect of the invention is directed to the use of titanium to improve selectivity (lower N2O make) of a copper chabazite SCR catalyst.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig- 1 shows NOx conversion and N2O selectivity for a Ti Cu zeolite in accordance with an embodiment of the invention together with a comparative Cu zeolite without Ti.
Fig- 2 shows NH3, NO and N2O over time for a Ti Cu zeolite in accordance with an embodiment of the invention together with a comparative Cu zeolite without Ti.
Fig. 3 shows H2-TPR (hydrogen temperature-programmed reduction) for a Ti Cu zeolite in accordance with an embodiment of the invention together with a comparative Cu zeolite without Ti.
Fig- 4 shows TEM images of a Ti zeolite (without Cu) in accordance with embodiments of the invention (from ICP, Ti content -1.5%). Scale is 50nm.
Fig. 5 shows TEM images of a Ti Cu zeolite in accordance with embodiments of the invention (from ICP, Ti content -1.5% and Cu - 3.5%). Scale is 50nm.
Fig. 6 shows NOx conversion (A) and N2O production (B) at 200°C for a Ti Cu zeolite in accordance with an embodiment of the invention together with a comparative Cu zeolite without Ti.
DETAILED DESCRIPTION OF THE INVENTION
One aspect of the invention is directed to a composite for treating a NOx-containing exhaust gas, the composite comprising (e.g., consisting essentially of or consisting of) a coppersubstituted zeolite and one or more of Ti, Zr, Y, Ce, Er and Nd.
N2O is an undesired by-product of the SCR process for the removal of NOx (also known as a deNOx process). High deNOx performance is required at high temperature (T > 450°C) without the onset of the undesired ammonia oxidation reaction. The composite of the invention shows improved selectivity and NOx performance compared to a reference copper zeolite that does not comprise one or more of Ti, Zr, T, Ce or Nd.
The composites of the invention show improved selectivity across a wide temperature range (150-550°C) as well as improved high temperature deNOx performance both for a fresh and hydrothermally aged catalyst.
Preferably, the composite has a low N2O selectivity. N2O selectivity is defined as the moles N2O formed divided by the moles of NOx (NOX defined as NO and NO2) converted. Lower N2O selectivity is improved N2O selectivity and desired because of the need to reduce N2O formation, a greenhouse gas. Fig. 1 shows improved N2O selectivity (lower N2O make) for the titanium copper zeolite, relative to the reference copper zeolite without titanium.
The invention encompasses the manufacture of a composite comprising (e.g., consisting essentially of or consisting of) a copper-substituted zeolite and one or more of Ti, Zr, Y, Ce, Er and Nd. The invention is not concerned with copper-substituted zeolites having framework Ti, Zr, Y, Ce, Er and/or Nd. In particular, the composite of the invention does not comprise framework titanium (also known as a titanated zeolite), i.e., where the Ti is part of the zeolite framework structure. The copper-substituted zeolite of the present invention has repeating TO4 tetrahedral units with T being Si and Al, i.e. an aluminosilicate zeolite. The inventors propose that the Ti, Zr, Y, Ce, Er and/or Nd (preferably titanium) is present on the surface of the zeolite (e.g. as TiCE nanoparticles) and/or in ion-exchange sites within the zeolite. The composite may comprise an aluminosilicate particle having a porous TiCE coating, e.g. a titania encapsulated zeolite particle, as illustrated in figures 4 and 5. The TiCE coating is understood to be porous since it does not prevent copper loading. The present disclosure will now be described further. In the following passages, different aspects/embodiments of the disclosure are defined in more detail. Each aspect/embodiment so defined may be combined with any other aspect/embodiment or aspects/embodiments unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.
One aspect of the invention is directed to a method for the manufacture of a composite comprising (e.g., consisting essentially of or consisting of) a (bare) zeolite and one or more of Ti, Zr, Y, Ce, Er and Nd (preferably titanium), the method comprising: (ii) providing a composition comprising an inorganic compound of one or more of Ti, Zr, Y, Ce, Er and Nd (preferably an inorganic titanium compound), a zeolite, and water, the composition having a pH of less than 7; and
(ii) adding a base to the composition, thereby increasing the pH of the composition and yielding the composite; wherein the zeolite has a CHA or an AEI framework.
It will be appreciated that copper can be added to the direct product of this method to yield the composite of the first aspect of the invention. This can be via incipient wetness or ion exchange, for example.
The inorganic compound of one or more Ti, Zr, Y, Ce, Er and Nd is preferably not an oxide. The inorganic compound may be a sulfate, an acetate or a nitrate and may form an oxide within the composition. Without being bound by theory, the inventors propose that the formation of the oxide in situ provides a more catalytically active composite.
In this embodiment, the composite is prepared by first combining the (bare, i.e. without Cu) zeolite and an inorganic compound under acidic conditions. Preferably the zeolite is the H-form zeolite, where H+ (protons) occupy ion-exchange sites within the zeolite, and not a copper loaded zeolite for example. A copper loaded composite may be obtained by a subsequent processing of the Ti zeolite composite, e.g. by an ion exchange step. We submit that the order of addition the copper has an effect on the structure of the resulting composite, e.g. Cu speciation. Hence the copper loaded composite of the invention is distinguishable from prior art composites where titanium is employed after copper.
In one embodiment the starting composition (before the base is added) comprises an inorganic titanium compound (e.g. titanyl sulfate, a zeolite (e.g. a CHA or AEI zeolite), optionally an acid (e.g. sulfuric acid), and water and has a pH of less than 7. The pH can be adjusted by modifying the concentration of the acid. The pH may be 6 or less, 5.5 or less, 5 or less, 4 or less, 3 or less or 2 or less.
In one embodiment the starting composition (before the base is added) comprises an inorganic zirconium compound (e.g. zirconium(IV) acetate), a zeolite (e.g. a CHA or AEI zeolite), optionally an acid (e.g. acetic acid), and water and has a pH of less than 7. The pH can be adjusted by modifying the concentration of the acid. The pH may be 6 or less, 5.5 or less, 5 or less, 4 or less, 3 or less or 2 or less.
In one embodiment the starting composition (before the base is added) comprises an inorganic yttrium compound (e.g. yttrium acetate), a zeolite (e.g. a CHA or AEI zeolite), optionally an acid (e.g. acetic acid), and water and has a pH of less than 7. The pH can be adjusted by modifying the concentration of the acid. The pH may be 6 or less, 5.5 or less, 5 or less, 4 or less, 3 or less or 2 or less.
In one embodiment the starting composition (before the base is added) comprises an inorganic cerium compound (e.g. cerium nitrate), a zeolite (e.g. a CHA or AEI zeolite), optionally an acid (e.g. nitric acid), and water and has a pH of less than 7. The pH can be adjusted by modifying the concentration of the acid. The pH may be 6 or less, 5.5 or less, 5 or less, 4 or less, 3 or less or 2 or less.
In one embodiment the starting composition (before the base is added) comprises an inorganic erbium compound (e.g. erbium acetate), a zeolite (e.g. a CHA or AEI zeolite), optionally an acid (e.g. acetic acid), and water and has a pH of less than 7. The pH can be adjusted by modifying the concentration of the acid. The pH may be 6 or less, 5.5 or less, 5 or less, 4 or less, 3 or less or 2 or less.
In one embodiment the starting composition (before the base is added) comprises an inorganic neodymium compound (e.g. neodymium acetate or nitrate), a zeolite (e.g. a CHA or AEI zeolite), optionally an acid (e.g. acetic acid or nitric acid), and water and has a pH of less than 7. The pH can be adjusted by modifying the concentration of the acid. The pH may be 6 or less, 5.5 or less, 5 or less, 4 or less, 3 or less or 2 or less.
The acid may be an inorganic acid such as sulfuric acid (H2SO4), hydrochloric acid (HC1), or nitric acid (HNO3). Since the composition comprises water, the acid is an aqueous acid.
The zeolite is typically an aluminosilicate zeolite, having a framework that consists essentially of aluminium, silicon and oxygen. The zeolite may have a molar silica to alumina ratio (SAR) of 5 or more, 10 or more or 15 or more, and/or the zeolite may have a molar silica to alumina ratio (SAR) of 40 or less, 30 or less or 20 or less. The zeolite may have a SAR of 15 to 25, such as 18 to 23, such as 19, 20, 21 or 22. The zeolite may comprise a chabazite (CHA) and/or an AEI zeolite. In a preferred embodiment, the zeolite has a molar silica to alumina ratio (SAR) of 10 to 30, preferably from 12-28 and more preferably from 14-25. In a further embodiment, the SAR is from 12-16, e.g., 14, from 18-22, e.g., 20, or from 22-27, e.g., 25. In a particularly preferred embodiment, the SAR is from 10-25, preferably from 12-22, even more preferably from 13-21.
The inorganic titanium compound may be titanyl sulfate (TiOSC ). Titanyl sulfate hydrolyzes to a gel of hydrated titanium dioxide. The method may comprise an initial step of forming the composition by combining titanyl sulfate with the zeolite, optionally acid and water.
The (starting) composition may be described with reference to the (sum) total dry weights of the inorganic titanium compound and the zeolite. The inorganic titanium compound may constitute at least 3wt%, at least 5wt%, at least 7wt% or at least 10wt% of the total dry weights of inorganic titanium compound and the zeolite. The inorganic titanium compound may constitute 50wt% or less, 40wt% or less, 30wt% or less, 20wt% or less or 10wt% or less of the total dry weight of the inorganic titanium compound and the zeolite.
Similarly, the composition may be described with reference to the ratio dry weight of the inorganic titanium compound: dry weight of zeolite, e.g. from 1 : 20 to 1 : 1 such as 1 : 15 to 1 : 5, such as 1 : 10.
Addition of the base increases the pH of the composition yielding the composite, e.g. a white residue of zeolite and titanium. The base may comprise ammonia, e.g. aqueous ammonia. The addition of the base may increase the pH of the composition to pH 3.5 or more, pH 4 or more or pH 4.5 or more, such as pH 3 to 7 or pH 4 to 6.
The composite may be isolated, that is separated from the rest of the composition, e.g. by filtration. The composite may be dried, e.g. at a temperature of from 100 to 200°C for a period of from 1 hour to 10 hours. The composite may be calcined, e.g. at a temperature of from 500 to 1000°C for a period of from 1 to 5 hours.
In one embodiment the method comprises:
(i) providing a composition comprising aqueous sulfuric acid (H2SO4) and the zeolite, the composition having a pH of less than 7 and the zeolite comprising zeolite particles having an outer surface; and (ii) adding titanyl sulfate (TiOSC ) and a base to the composition, thereby increasing the pH of the composition and depositing titanium dioxide (TiCh) on the outer surface of the zeolite particles, wherein the zeolite has a CHA or AEI framework.
In some preferred embodiments, the method further comprises a step of adding iron and/or copper to the composite by ion exchange. As described herein, iron and/or copper exchanged zeolites are particularly preferred as NH3-SCR catalysts.
In a further embodiment, the invention relates to a method of preparing a composite (e.g. a composite as herein described), said method comprising:
(i) firstly, exchanging one or more of Ti, Zr, Y, Ce, Er and Nd (preferably Ti) into a molecular sieve, and then
(ii) secondly, incorporating copper into the molecular sieve.
Exchanging one or more of Ti, Zr, Y, Ce, Er and Nd (preferably Ti) can be performed any known technique such as ion exchange, impregnation, isomorphous substitution, etc. Preferably exchanging one or more of Ti, Zr, Y, Ce, Er and Nd (preferably Ti) is performed through ion exchange.
The invention also resides in a composite producible by the methods above. The composite is an intermediate in the preparation of copper substituted product and comprises a (bare) zeolite and one or more of titanium, zirconium, yttrium, cerium, erbium and neodymium, wherein the zeolite has a CHA or AEI framework.
In some embodiments, the composite comprises a CHA zeolite having a SAR of from 10 to 30, 15 to 25, 18 to 20, preferably from 12-28 and more preferably from 14-25. In a further embodiment, the SAR is from 12-16, e.g., 14, from 18-22, e.g., 20, or from 22-27, e.g., 25. In a particularly preferred embodiment, the SAR is from 10-25, preferably from 12-22, even more preferably from 13-21. In other embodiments described herein, the composite comprises an AEI zeolite having a SAR of from 10 to 30, 15 to 25, 18 to 20, preferably from 12-28 and more preferably from 14-25. In a further embodiment, the SAR is from 12-16, e.g., 14, from 18-22, e.g., 20, or from 22-27, e.g., 25. In a particularly preferred embodiment, the SAR is from 10- 25, preferably from 12-22, even more preferably from 13-21. The composite may comprise one or more of Ti, Zr, Y, Ce, Er and Nd at a total loading of at least 0.5wt% based on oxide, preferably at least lwt% based on oxide, such as from 0.5 to 10wt% based on oxide. In one embodiment, the composite comprises one or more of Ti, Zr, Y, Ce, Er and Nd at a total loading of between 0.5wt% to 15 wt% based on oxide, preferably from 1 to 10 wt% based on oxide, most preferably from 2 to 7 wt% based on oxide.
Preferably, the composite comprises titanium at a loading of at least 0.5wt% based on oxide, preferably at least lwt% based on oxide, such as from 1 to 10wt% based on oxide. The Ti composite may comprise at least 0.5wt% TiCE, preferably at least lwt% TiCE, such as from 1 to 10wt% TiCE. The Ti composite may comprise 10wt% TiCE or less, such as 5wt% TiCE, or less, such as 3wt% TiCE or less. The examples demonstrate composites having 1.3 and 2.6wt% TiO2.
The composite of the invention may comprise copper at a loading of 2wt% or more, 3wt% or more, 4wt% or more or 5wt% or more, such as from 2 to 5wt% Cu. In particular, the composite may comprise a CHA zeolite (e.g. SAR 10-30, 12-28, 14-25 or 18-20) having a titanium loading of from l-3wt% and a copper loading of from 3-5wt%.
In one aspect, the composite of the invention as described herein does not comprise Mn, preferably does not comprise Mn or Fe, more preferably does not comprise Mn, Fe or Si, even more preferably does not comprise Mn, Fe, Si, Ce, or Sn, and most preferably does not comprise Mn, Zr, Fe, Si, Ce, or Sn.
In a further aspect of the present invention, there is provided a catalyst article for the treatment of an exhaust gas, the catalyst article comprising the composite as described herein.
In yet a further aspect, there is provided a method for the treatment of an exhaust gas, the method comprising contacting an exhaust gas with the catalyst article described herein.
In a further aspect of the present invention, there is provided a method for reducing N2O formation in the catalytic treatment of an exhaust gas (e.g., an exhaust gas comprising NOX and ammonia), wherein the exhaust gas is contacted with a composite described herein, a catalyst article described herein (e.g., a catalyst article comprising the composite as described herein) or a composite produced by the method as described herein.
The method may comprise contacting an exhaust gas containing NOX and optionally NH3 with the catalyst article described herein to selectively reduce at least a portion of the NOX into N2 and H2O and to oxidize at least a portion of the NH3 (when present). Thus, in one embodiment, the catalyst article can be formulated to favour the reduction of nitrogen oxides with a reductant (i.e., an SCR catalyst). Examples of such reductants include hydrocarbons (e.g., C3-C6 hydrocarbons) and nitrogenous reductants such as ammonia and ammonia hydrazine or any suitable ammonia precursor, such as urea ((NEE^CO), ammonium carbonate, ammonium carbamate, ammonium hydrogen carbonate or ammonium formate).
In yet a further embodiment of the present invention, the exhaust gas may be generated by an internal combustion engine powdered by a fuel mixture containing air; and hydrogen and/or ammonia, also known as a hydrogen internal combustion engine or an ammonia internal combustion engine.
The invention also finds application in NOX abatement of exhaust gases produced by internal combustion engines powdered by hydrogen and/or ammonia fuel.
A hydrogen internal combustion engine is well-known to those skilled in the art and may be considered to be a modified version of a conventional gasoline (petrol) or diesel powered internal combustion engines. The fuel of the mixture of air and fuel is a gaseous fuel comprising a majority fuel mass of hydrogen (H2). Preferably an internal combustion engine configured to run on a majority fuel mass of hydrogen (H2) is configured to run on a fuel comprising >70 vol% H2, such as >90 vol% H2, >95 vol% H2, >99 vol% H2, and more preferably a fuel consisting essentially of H2. The balance of the fuel mass may consist of hydrocarbons such as methane, diesel and/or gasoline.
Although a hydrogen internal combustion engine can operate essentially free of carbonbased emissions in its exhaust gas (e.g. CO or CO2) or unburned hydrocarbons (HCs), some trace emissions may still exist due to combustion of engine additives, such as lubricating oil. Unburned hydrogen in its exhaust gas is nevertheless a problem for hydrogen internal combustion engines, as are NOX which arise from the combustion of the fuel in air (which is approximately 78 vol% nitrogen) as is known in respect of conventional internal combustion engines. At the same time, exhaust gases of hydrogen internal combustion engines are typically cooler than gasoline or diesel-powered engines. This can impact on the efficiency of catalytic aftertreatment of H2 and NOx in exhaust gas, as well as on remedial processes such as selective catalytic reduction (SCR) catalyst de-sulphation adopted in diesel exhaust systems that require relatively high temperatures and sometimes also a reducing atmosphere to desulphate. Additionally, a hydrogen internal combustion engine produces a relatively large amount of water as a by-product of combustion. Typically, a hydrogen internal combustion engine exhaust gas may comprise from about 20-30 vol% water as steam.
Similarly, ammonia (NH3) is also considered as a fuel for direct use in a combustion system, or as an efficient hydrogen carrier. Emissions from ammonia combustion are likely to contain N2O, NOx, and unburned ammonia. In addition, the water content in the exhaust gas produced from ammonia combustion will also be significantly higher than that emitted by conventional gasoline (petrol) or diesel powered internal combustion engines.
Known SCR catalysts may be used for NOX abatement in the exhaust of a hydrogen and/or ammonia internal combustion engines. However, the relatively high water content of the exhaust of a hydrogen or ammonia internal combustion engine negatively impacts the activity of conventional SCR catalysts resulting in reduced catalyst activity and performance. The presence of water inhibits the NOX conversion rate due to water being adsorbed on the active sites of the catalyst. The adsorbed water on catalysts surface hinders adsorption of reactants and the hydroxyl (OH) groups derived from dissociative adsorption of water could lower reactivity of active sites, thereby reducing catalytic activity. Surprisingly, the inventors of the present invention have found that the catalyst article according to the present invention exhibits improved catalytic activity and therefore improved NOX conversion rates when treating an exhaust gas having a relatively high water content. Without wishing to be bound by any theory, it is believed that the presence of one or more of Ti, Zr, Y, Ce, Er and Nd (preferably titanium), reduces the catalyst deactivation resulting in improved NOX conversion rates and improved selectivity (lower N2O make) when treating an exhaust gas in the presence of water.
Accordingly, in a further aspect of the present invention, there is provided a system for treating an exhaust gas produced by a hydrogen or ammonia internal combustion engine, wherein the exhaust gas comprises NOx, and wherein the system comprises: a hydrogen internal combustion engine or an ammonia internal combustion engine; a a catalyst article as described herein; and a source of reductant, wherein the reductant source is upstream of the catalyst article.
A further benefit of the catalyst article in this aspect of the invention is that the coppersubstituted zeolite SCR catalyst is more sulphur tolerant, i.e. it either is less readily sulphated or, if sulphated, remains relatively more active than alternative SCR catalysts. For this reason, the catalyst article may require less frequent desulphation events to maintain its activity, thus improving the overall fuel economy of the system, i.e. energy is less frequently required to increase the catalyst temperature and optionally increased hydrogen reductant enrichment in the exhaust gas is less frequently needed to desulphate the catalyst.
In yet a further aspect of the invention, there is provided a method for reducing N2O formation in the catalytic treatment of an exhaust gas of a hydrogen or ammonia internal combustion engine, wherein the exhaust gas is contacted with a composite described herein, a catalyst article described herein (e.g., a catalyst article comprising the composite as described herein) or a composite produced by the method as described herein.
As illustrated in the Examples, the inventors have found that the method as described above is unexpectedly effective at mitigating formation of nitrous oxide (N2O) during treatment of exhaust gas obtained from a hydrogen engine.
EXAMPLES
General Method
A bare composite (without copper) was prepared following a preparation adapted from Zhang et al. (Microporous and Mesoporous Materials 255 (2018) 61-68). Zeolite (AZM16 = CHA having an SAR of 19) was mixed with titanium(IV) oxy sulfate solution (equivalent to deionized water and sulfuric acid) followed by addition of ammonia solution to adjust the pH to pH 4.5. A white residue formed and was washed with distilled water, followed by drying at 105°C for 8 hours and calcination at 650°C for 2 hours. The titanium(IV) oxysulfate was employed to generate the equivalent of 5 or 10wt% TiCh in situ. ICP (inductively coupled plasma) spectroscopy using TiCh as base give 1.3 and 2.6 % Ti respectively for the resulting composites.
The calcined composite was loaded with copper by ion-exchange (3 or 4wt%).
The composite was tested in the form of powder as fresh (F500C/2h) and after HDD ageing conditions (LHA650C/50h) under the following conditions: i) NO and NH3 (ANR 1.1) in O2 (10%) + H2O (8%). T= 150- 500°C, heating rate= 5°C/min, SV = 60kh-l; ii) NO (500ppm), CO (350ppm), CO2 (8%), O2 (10%), H2O (8%). at 175°C, NH3 injection (700ppm) after 5 min with a total SV of 60kh-l.
Referring to figures 1 and 2, NOX conversion is similar until ~400°C for the copper-substituted chabazites (3wt% Cu) with and without Ti. The composite of the invention maintains high NOx conversion above ~400°C. Moreover, the titanium containing composite has lower N2O over the whole temperature range. Hence, the composite of the invention shows significant improvements in selectivity (lower N2O make) across the whole temperature region of the experiments (150-500°C). This surprising benefit is not due to minor differences in Cu loadings as shown in figure 3. H2-TPR confirmed Cu loadings and minimal differences in speciation. In fact, copper loading was estimated via NO and NH3 reduction and found to be 2.9% for the Ti containing product and 3. lwt% for the reference (without Ti)
The same Ti-doped CHA SAR 19 material was exchanged with 4% Cu and formulated into a washcoat and then coated (2.4g/in3) into a honeycomb cordierite substrate for activity testing in the form of a monolith. The same benefits in terms of selectivity and high temperature deNOx performance were observed after LHA650C/50h. The benefits are retained after hydrothermal ageing.
TEM images of the Ti containing zeolite (without Cu) showed the presence of Ti on the surface of the zeolite particles (figures 4A to 4C). TEM images of the Ti containing copper-substituted zeolite showed the presence of Ti on the surface of the zeolite particles and copper within the particles (figures 5A to 4D).
H2-ICE testing
The composite was also tested under H2-ICE conditions. For this type of application, treatment of exhaust gas has to occur under more demanding conditions, i.e. higher water content in the exhaust feed, which can affect both NOx reduction performance and selectivity. Therefore, Improved NOx conversion and selectivity are still desired features for alternative methods to treat exhaust gas and new catalytic articles.
The composite was tested in the form of powder as fresh (F500C/2h) under the following conditions: i) NO and NH3 (ANR 1.1) in O2 (10%) + H2O (20 vol% H2O). T= 150- 500°C, heating rate= 5°C/min, SV = 60kh-l. The results of this testing are compared to those obtained in the presence of 10 vol% H2O.
Referring to Figures 6A and B, NOX conversion is similar at 200°C for the copper-substituted chabazites (3wt% Cu) with and without Ti for both set of conditions (10 vol% H2O and 20 vol% H2O). For both catalysts, the NOx conversion is mildly affected by the increased water content in the feed. However, the titanium containing composite has lower N2O production. Hence, the composite of the invention maintains significant improvements in selectivity (lower N2O make) even under more demanding conditions such as those expected for H2-ICE applications.
As used herein, the singular form of “a”, “an” and “the” include plural references unless the context clearly dictates otherwise. The use of the term “comprising” is intended to be interpreted as including such features but not excluding other features and is also intended to include the option of the features necessarily being limited to those described. In other words, the term also includes the limitations of “consisting essentially of’ (intended to mean that specific further components can be present provided they do not materially affect the essential characteristic of the described feature) and “consisting of’ (intended to mean that no other feature may be included such that if the components were expressed as percentages by their proportions, these would add up to 100%, whilst accounting for any unavoidable impurities), unless the context clearly dictates otherwise.
By ‘consisting essentially of, the basic and novel characteristics of the invention are a composite comprising a copper-substituted zeolite and one or more of Ti, Zr, Y, Ce, Er and Nd. Addition of other metals to the copper-substituted zeolite can affect the NOX conversion and selectivity of the resulting catalyst and thus do not form part of the basic and novel characteristics of the invention. For example, in one aspect, the composite of the invention as described herein does not comprise Mn, preferably does not comprise Mn or Fe, more preferably does not comprise Mn, Fe or Si, even more preferably does not comprise Mn, Fe, Si, Ce, or Sn, and most preferably does not comprise Mn, Zr, Fe, Si, Ce, or Sn.
The foregoing detailed description has been provided by way of explanation and illustration and is not intended to limit the scope of the appended claims. Many variations of the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art and remain within the scope of the appended claims and their equivalents.