BLEACH CATALYST

Abstract

A bleach catalyst suitable for use in automatic dishwashing comprising a mixed metal oxide.

Claims

1. An automatic dishwashing composition comprising a heterogenous bleach catalyst comprising a mixed metal oxide.

2. The automatic dishwashing composition according to claim 1, wherein one or more of the metal oxide(s) of the heterogenous bleach catalyst is a transition metal.

3. The automatic dishwashing composition according to claim wherein the heterogenous bleach catalyst comprises a transition metal oxide, preferably copper, manganese, iron, and/or zinc, on a zirconium oxide carrier.

4. The automatic dishwashing composition according to claim 3, wherein the transition metal oxide of the heterogenous bleach catalyst is present in an amount from 1 to 50 mol %, preferably from 2 to 20 mol % relative to the metal oxide carrier.

5. The automatic dishwashing composition according to claim 1, wherein the heterogenous bleach catalyst comprises copper oxide on a zirconium oxide carrier.

6. The automatic dishwashing composition according to claim 5, wherein the copper surface area of the heterogenous bleach catalyst is less than 1 m.sup.2/g.

7. The automatic dishwashing composition according to claim 1, wherein the heterogenous bleach catalyst has been calcined.

8. The automatic dishwashing composition according to claim 1, wherein the heterogenous bleach catalyst has been acid treated.

9. A method of preparing a heterogenous mixed metal oxide catalyst suitable for use in automatic dishwashing, the method comprising: precipitating two or more metal salts; forming the mixed-metal oxalate from the precipitate; calcining the precipitate to form the mixed metal oxide; and treating the mixed metal oxide with acid, and wherein the heterogenous bleach catalyst comprises copper oxide on a zirconium oxide carrier.

10. The method according to claim 9, wherein the copper oxide of the heterogenous bleach catalyst is present in an amount from 1 to 50 mol % relative to the zirconium oxide carrier.

11. The method according to claim 9, wherein the copper surface area of the copper oxide of the heterogenous bleach catalyst is greater than zero, preferably greater than 0.01 m.sup.2/g and less than 4 m.sup.2/g.

Description

EXAMPLES

[0045] Precipitate Preparation

[0046] Cu(NO.sub.3).sub.2.3H.sub.2O (0.01 mol) and ZrO(NO.sub.3).sub.2 hydrate (0.01 mol) were dissolved separately in absolute ethanol (100 mL) at room temperature in air. After dissolution, the two solutions were combined in a 400 mL beaker and stirred at room temperature, in air. Oxalic acid dihydrate (3.03 g, 0.024 mol, solid) was subsequently added to this solution, resulting in the immediate precipitation of the metal oxalates. This precipitation is evidenced by a visual change in the appearance of the solution, with a light blue opaque mixture being formed instantaneously. The solution was stirred for an additional 2 hours at room temperature, in air. The oxalate gel was then collected via filtration. This cake was subsequently dried at 110° C. in a static air oven for 16 hours. After drying, the remaining solid is crushed into a blue fine powder using a mortar and pestle.

[0047] This procedure was successfully repeated for the synthesis of Cu—Zr, Mn—Zr, Fe—Zr and Zn—Zr oxalate precursors.

[0048] Calcination

[0049] The oxalate precursors were subsequently calcined under flowing air to produce the desired active material. For the preparation of a CuO.sub.x/ZrO.sub.v catalyst the Cu—Zr oxalate was added to a Coors™ high alumina combustion boat and calcined in a Carbolite™ tube furnace. The tube furnace was heated to 550° C. from ambient temperature at a heating rate of 10° C./min. Once at 550° C., the temperature of the furnace was maintained for 2 hours. During the treatment air was passed over the catalyst at a rate of 50 mL/min. Once the furnace was cooled to room temperature, the powdered catalyst was collected. The decomposition of the Cu—Zr oxalate precursor was evidenced by a change in colour to a darker green and mass loss.

[0050] Acid Treatment

[0051] The removal of surface metal was subsequently achieved through washing of the material with concentrated HNO.sub.3. The corresponding metal oxide (0.2 g) was stirred in HNO.sub.3 (70 wt %, 200 mL) for 2 hours at room temperature. The catalyst was collected and separated from the acid by centrifugation and decanting of the acidic solution. Deionised water was added and the catalyst resuspended by shaking, before being centrifuged again and decanted off.

[0052] This process was repeated 3 more times until the water post centrifugation had a pH of 7. The catalyst was dried in a static air furnace at 110° C. for 16 h. The catalyst was collected as a dry powder.

[0053] Analysis and Results

[0054] Bleaching Evaluation of Tea Stains

[0055] Sodium percarbonate (1.5 g), TAED (0.45 g) and MGDA (0.2 g) were added to tap water (1.8 L, 5° dH, 89 ppm CaCO.sub.3) at 50° C. under vigorous stirring. Tea cups are pre-stained and evaluated according to the IKW procedure (Recommendations for the Quality Assessment of the Cleaning Performance of Dishwasher Detergents (Part B, Update 2015) German Cosmetic, Toiletry, Perfumery and Detergent Association “Industrieverband Koerperpflege-and Waschmittel” IKW)—Working Group Automatic Dishwashing Detergents Sofw journal|142|06/16 33-48). A pre-stained tea cup is half submerged in the wash solution and the catalyst (3 mg) was added. After 8 minutes the cup was removed from the beaker and rinsed three times in fresh tap water to remove any bleaching solution residue and to stop bleaching continuing in the cup after the wash, the bleaching performance was visually evaluated using a 1-10 scale, with 1 being no visible bleaching activity and 10 being a completely bleached surface.

[0056] A range of copper catalysts with molar ratios from 50% to 1% copper were tested for bleaching performance on tea stains on a cup surface before acid treatment.

[0057] The ZrO.sub.2 support material, together with the 50 mol %, and 10 mol % copper catalysts were re-tested for bleaching performance after acid treatment.

[0058] The results are shown in Table 1.

TABLE-US-00001 TABLE 1 Bleaching Catalyst Composition Performance Score No catalyst 2 Mn(TACN) 6 ZrO.sub.2 2 50 mol % Cu.sub.x/ZrO.sub.y 2 30 mol % Cu.sub.x/ZrO.sub.y 2 10 mol % Cu.sub.x/ZrO.sub.y 3 5 mol % Cu.sub.x/ZrO.sub.y 4 2.5 mol % Cu.sub.x/ZrO.sub.y 3 1 mol % Cu.sub.x/ZrO.sub.y 2 ZrO.sub.2 AT 2 50 mol % Cu.sub.x/ZrO.sub.y AT 4 10 mol % Cu.sub.x/ZrO.sub.y AT 5

[0059] Bleaching activity decreases at low copper concentrations. This is expected to be due to the reduced number of active sites on the catalyst which promote bleaching.

[0060] Copper Surface Area Analysis

[0061] Copper surface area analysis was carried out using ChemBET Pulsar Quantachrome. The catalyst (ca. 100 mg) was loaded into glass tube plugged either side with quartz wool. Temperature programmed reduction was then carried out to reduce copper oxide to copper metal. Hydrogen (150 mL/min) was flowed over the catalyst while it was heated to 140° C. at 10° C./min. Analysis of the sample was then started as it was further heated to 280° C. at 1° C./min. When the temperature reached the desired temperature, it was maintained for 10 mins before cooling. Low temperatures and slow ramp rates were chosen to reduce sintering of the copper particles on the surface.

[0062] After cooling the gas was switched to helium (150 mL/min) and the sample heated to 65° C. Analysis was started and regular pulses of N.sub.2O (113 μL) was introduced into the gas stream. As copper reduces N.sub.2O to N.sub.2, the amount of N.sub.2 produced was recorded. When the N.sub.2 peaks stayed a consistent size, the N.sub.2O was switched to N.sub.2, and 4 regular pulses of N.sub.2 (113 μL) were then used to calibrate against. The total volume of N.sub.2 produced during the experiment was used to calculate the copper surface area.

TABLE-US-00002 TABLE 2 Copper Surface Catalyst Composition Area (m.sup.2/g) 10 mol % Cu.sub.x/ZrO.sub.y 4.6 10 mol % Cu.sub.x/ZrO.sub.y AT 0.2 50 mol % Cu.sub.x/ZrO.sub.y 6.4 50 mol % Cu.sub.x/ZrO.sub.y AT 0.4

[0063] X-Ray Powder Diffraction (XRPD) Analysis

[0064] X-ray powder diffraction was used to identify bulk phases present in the catalyst both pre- and post-acid treatment. The diffraction patterns are set out in FIG. 1.

[0065] Peaks denoted with a diamond match the ICDD database 00-027-0997 for cubic zirconia, peaks denoted with a circle match the ICDD database 01-089-5895 for monoclinic Cu(II)O, which were only present in the 50 mol % CuO.sub.x/ZrO.sub.2 pre-acid treated catalyst. This is indicative that large CuO particles, which could be responsible for the decomposition of H.sub.2O.sub.2 to H.sub.2O and O.sub.2, are present in this material.

[0066] Evidentially, these species are no longer present after acid treatment and peaks denoted with a triangle are now present in 50 mol % CuO.sub.x post-acid treatment sample. These peaks match the ICDD database 00-043-0953 for orthorhombic CuZrO.sub.3 and indicates that the acid treatment also leads to the formation of more intimately mixed Cu—Zr phases in the catalyst.

[0067] X-Ray Photoelectron Spectroscopy (XPS) Analysis

[0068] X-ray photoelectron spectroscopy was used to identify the surface species of the catalyst for: (a) 50 mol % CuO.sub.x/ZrO.sub.2 and (b) 10 mol % CuO.sub.x/ZrO.sub.2. The analysis is shown in FIG. 2.

[0069] Post-acid treatment the intensity of the copper peaks decrease as the acid treatment successfully removes copper from the surface of the catalyst. The main peak observed at binding energy (BE)=934 eV is indicative of CuO, while for the 50 mol % CuO.sub.x/ZrO.sub.2 pre acid treatment there are 2 peaks at BE 944 and 941 eV, which indicates the presence of Cu(II)O. The same peak now is more diffuse for 10 mol % CuO.sub.x/ZrO.sub.2, which suggests the presence of Cu(II)(OH).sub.2.

[0070] Overall, the characterisation of the copper catalyst has identified CuO and Cu(OH).sub.2 species on the surface. The acid treatment appears to remove larger CuO particles and increase the presence of OH species giving the more active bleach catalyst. This suggests that Cu(OH).sub.2 may be the active species for bleaching and/or the removal of CuO could decrease the competing reaction which leads to the decomposition of H.sub.2O.sub.2.

[0071] Summary of Results

[0072] The results show that mixed metal oxides are an active bleach catalyst for removal of tea stains from a solid surface and that treatment of these catalysts with a concentrated acid increases the bleach activity of both high and low copper concentration catalysts further.

[0073] A new heterogeneous bleaching catalyst has therefore been developed using abundant transition metals and that demonstrates technical performance close to that of MnTACN and homogeneous catalysts used currently in ADW formulations.

[0074] The invention is defined by the claims.