TW202313194A - Copper-containing hydrogenation catalysts - Google Patents

Abstract

The present invention provides a method for the conversion of an aldehyde to the corresponding alcohol using a reduced catalyst, wherein the reduced catalyst is formed by reducing an oxidic catalyst, the oxidic catalyst comprising zinc and copper on an Al ₂O ₃support, wherein the oxidic catalyst comprises: 1-15 wt% ZnO; and 5-30 wt% CuO; in each case based on the total weight of the oxidic catalyst; wherein together, ZnO, CuO and Al ₂O ₃make up ≥ 95 wt% of the oxidic catalyst.

Description

Copper-containing hydrogenation catalyst

The present invention relates to copper-containing hydrogenation catalysts, which are especially suitable for the hydrogenation of aldehydes to alcohols.

Catalytic hydrogenation of aldehydes is of commercial importance. For example, hydroformylation of olefins followed by catalytic hydrogenation of the resulting aldehydes is the basis for a convenient and major industrial route to detergent alcohols. It is known to use copper-based catalysts for this hydrogenation step. Typically, these catalysts are formed by precipitation and have a relatively uniform distribution of the metal throughout the catalyst.

EP 0 424 069 A1 (Engelhard Company) describes catalysts in powdered form comprising major amounts of oxides of copper and zinc and small amounts of aluminum oxide, wherein at least 80% of the total pore volume is composed of pores with a diameter greater than 80 Å supply. The catalysts are prepared by precipitation.

US2015/0314273 A1 (Clariant International Ltd) describes a method of preparing a tablet-shaped catalyst by combining (i) an aqueous solution of at least one copper compound, aluminum compound and optionally a transition metal compound, and ( ii) combining at least one carbonate-containing aqueous solution to form a precipitate, isolating and drying the precipitate, and tableting the precipitate. In the examples, the precipitated catalyst was formed from copper nitrate, manganese nitrate and aluminum nitrate, with copper as the main element.

CN103506125A (China Petroleum and Chemical, etc.) describes a catalyst for gas-phase hydrogenation of propionaldehyde, wherein the catalyst components are mainly copper oxide, zinc oxide, aluminum oxide and additives. The catalyst has the formula CuZn _a Al _b M _c O _x , wherein a is 1 to 3, b is 0.005 to 0.1, c is 0.003 to 0.1 and M is K, Mg, Ca, Sr or Ba. The catalyst is produced by co-precipitation method.

CN105080549A (China Petroleum and Chemical etc.) describes a catalyst for the gas phase hydrogenation of octenal comprising 25 to 35% copper oxide, 45 to 60% zinc oxide, 2 to 10% aluminum oxide, 2.2 to 10% oxide Silicon and 0.01 to 1% additives. The catalyst is prepared by precipitation method.

CN106582660A (Wanhua Chemical Group Co Ltd) describes a method of preparing a catalyst for the hydrogenation of aldehydes. The method involves forming a mixed salt solution containing copper salt and zinc salt to an aqueous dispersion of nano-alumina, precipitating in a controlled pH and temperature range, followed by drying, ingot making and calcining to obtain a catalyst.

While many of the catalysts reported for aldehyde reduction are precipitated catalysts, the use of supported catalysts is also known. In these catalysts, the active metal (eg, copper) is distributed in a shell on the surface of the support rather than in the bulk. Supported catalysts offer the advantage that they generally require lower amounts of metals than precipitated catalysts.

WO99/51340 (Imperial Chemical Industries PLC) describes copper catalysts suitable for various reactions including hydrogenation. The catalysts are prepared by impregnating a porous transitional alumina support with an aqueous solution of copper amine carbonate complex, followed by drying and calcination.

WO2016/160921 (BASF Corporation) describes a method of forming a catalyst by impregnating a metal oxide support with an aqueous solution comprising a copper salt and a C3-C6 polyfunctional carboxylic acid, followed by drying and heat treatment of the impregnated support. The resulting catalyst comprises 5 to 50% by weight copper oxide.

Despite the advantages offered by supported copper catalysts in terms of low copper content, there is still the disadvantage of gradual deactivation of these catalysts over time. Furthermore, in the specific case of butyraldehyde to butanol _conversion , _the supported copper catalyst showed an undesired level of trimer by-products ( _CH3CH2CH2CH ( ^OnBu ) ₂ ) (hereinafter referred to as "acetal trimer"). There is a need for alternative catalysts for the conversion of aldehydes to alcohols that have low active metal loading and are less prone to deactivation. The present invention addresses this need.

The present inventors have now found that doping copper supports on alumina catalysts with zinc provides catalysts with high activity in the conversion of aldehydes to alcohols with low deactivation rates and in the case of butyraldehyde to butanol conversion , producing a low content of acetal trimer by-products.

In a first aspect, the invention relates to an oxidation catalyst comprising zinc and copper on an alumina (Al ₂ O ₃ ) support, wherein the oxidation catalyst comprises: 1 to 15% by weight ZnO; and 5 to 30 % by weight CuO; in each case based on the total weight of the oxidation catalyst; wherein ZnO, CuO and Al ₂ O ₃ together constitute > 95% by weight of the oxidation catalyst.

As used herein, the term "oxidation catalyst" means a catalyst in which substantially all of Zn and Cu are present as oxides.

In a second aspect, the present invention relates to a method for producing an oxidation catalyst, comprising the following steps: (i) impregnating the alumina support with an impregnation solution comprising a copper salt; (ii) drying and optionally calcining the product of step (i); (iii) impregnating the product of step (ii) with an impregnation solution comprising a zinc salt; (iv) drying and calcining the product of step (iii); Wherein the oxidation catalyst produced after step (iv) is the catalyst according to the first aspect.

In a third aspect, the present invention relates to a method of manufacturing an oxidation catalyst, which includes the following steps: (i) impregnating the alumina support with an impregnation solution comprising a zinc salt; (ii) drying and optionally calcining the product of step (i); (iii) impregnating the product of step (ii) with an impregnation solution comprising a copper salt; (iv) drying and calcining the product of step (iii); Wherein the oxidation catalyst produced after step (iv) is the catalyst according to the first aspect.

In a fourth aspect, the present invention relates to a method of manufacturing an oxidation catalyst, which includes the following steps: (i) impregnating the alumina support with an impregnating solution comprising a copper salt and a zinc salt; (ii) drying and calcining the product of step (i); Wherein the oxidation catalyst produced after step (ii) is the catalyst according to the first aspect.

The methods according to the second, third and fourth aspects are each suitable for producing the catalyst according to the first aspect. In each case, it is preferred that one or both of the copper salt and the zinc salt are nitrates. If the calcination step is carried out at a temperature not exceeding 350° C., residual nitrates remain in the oxidation catalyst. The presence of nitrate is believed to have a beneficial effect on selectivity; catalysts with residual nitrate were shown to produce lower levels of acetal trimer in the butyraldehyde to butanol process.

Once installed in the reactor, the oxidation catalyst is typically activated in situ by reducing some or all of the CuO to Cu metal using a _H2- containing feed. During this step, some of the ZnO may be converted to Zn. However, alumina is not reduced. Activation can be performed in gas or liquid phase. The result is a catalyst in which some or all of the Cu exists as Cu(0) crystallites. This catalyst is referred to herein as a "reduction catalyst". Exemplary methods for liquid phase activation of catalysts are described in WO2020/053555 (Johnson Matthey Davy Technologies Limited).

In a fifth aspect, the present invention relates to a reduction catalyst formed by reducing an oxidation catalyst.

In a sixth aspect, the present invention relates to a method for converting an aldehyde into a corresponding alcohol using a catalyst, wherein the reduction catalyst according to the sixth aspect is used as the catalyst. The process is preferably carried out with a liquid feed. A particularly preferred aldehyde is butyraldehyde.

Any subheadings are included for convenience only and should not be construed as limiting the invention in any way.

Catalysts In a first aspect, the invention relates to an oxidation catalyst comprising zinc and copper on an alumina support, wherein the oxidation catalyst comprises: 1 to 15% by weight ZnO; and 5 to 30% by weight CuO; In each case, based on the total weight of the oxidation catalyst; wherein ZnO, CuO and Al ₂ O ₃ together constitute ≥ 95% by weight of the oxidation catalyst.

The support is alumina (Al ₂ O ₃ ). The support preferably comprises at least 95% by weight alumina, preferably at least 98% by weight alumina. The support may contain low levels (less than 5% by weight) of impurities, such as silicon dioxide.

As will be appreciated by those skilled in the art, alumina takes various forms depending on the temperature at which it is calcined. Different forms of alumina include alpha-alumina, gamma-alumina, and theta-alumina. Alumina can be in a single form or a mixture of different forms. A preferred alumina is gamma alumina.

Preferably, ZnO, CuO and Al ₂ O ₃ together constitute ≧97 wt%, such as 98 wt%, of the oxidation catalyst. In some embodiments, ZnO, CuO, and Al ₂ O ₃ make up ≧99% by weight of the oxidation catalyst. _The ZnO, CuO, and _Al2O3 contents of the catalyst can be measured by inductively coupled plasma mass spectrometry (ICP) or by X-ray fluorescence (XRF), and then calculated The relative amounts of ZnO, CuO and Al ₂ O ₃ are determined, in each case, assuming that the elements are all present as oxides. This is a reasonable assumption since the catalyst fabrication route described in more detail later produces a catalyst by impregnating an alumina support with zinc and copper salts, followed by drying and calcination. Zinc and copper salts already contain the metal in the positively oxidized state (Zn(II) and Cu(I) or Cu(II)) and are calcined at elevated temperatures, usually in an atmosphere containing oxygen (e.g. air) , which will force any Cu(I) to become Cu(II). For this reason, it can be assumed that Zn, Cu and Al are present as ZnO, CuO and Al ₂ O ₃ .

Preferably, the oxidation catalyst comprises 1 to 15% by weight of ZnO and 15 to 25% by weight of CuO, in each case based on the total weight of the oxidation catalyst; wherein ZnO, CuO and _{Al2O3 together} constitute the oxidation catalyst Medium ≥ 95% by weight. Catalyst systems comprising 5 to 12.5% by weight ZnO and 15 to 25% by weight CuO are particularly preferred.

In preferred embodiments, the oxidation catalyst comprises residual nitrates. The presence of nitrate can be inferred by the presence of peaks related to NOx, i.e., 30 amu (NO ⁺ ), 44 amu (N ₂ O ⁺ ) and 46 amu (NO ₂ ⁺ ), as measured by TGA-MS Measurement. The total nitrogen content can be determined by CHN analysis. It was unexpectedly shown that the presence of nitrate provides a catalyst that is more selective and exhibits a lower content of acetal trimer when used for the conversion of butyraldehyde to butanol. Preferably, the oxidation catalyst contains >250 ppm nitrogen as measured by CHN analysis. In some embodiments, the oxidation catalyst comprises >500 ppm nitrogen, such as >1000 ppm nitrogen.

The catalysts described herein can be used as hydrogenation catalysts. It is particularly suitable for the conversion of aldehydes (including α,β-unsaturated aldehydes) to the corresponding alcohols. In the case of α,β-unsaturated aldehydes, hydrogenation of the carbon-carbon double bond can also take place, as for example in the conversion of 2-ethyl-3-propylacrolein to 2-ethylhexanol.

The catalysts described herein can be used in liquid phase or gas phase aldehyde hydrogenation, but are particularly useful in liquid phase aldehyde hydrogenation. Preferably, the catalyst is in the form of pellets, granules or extrudates (eg trilobal or quadrilobal). These catalysts can be prepared by impregnating an alumina support in the form of pellets, granules or extrudates with Cu and Zn salts. Preferably, the catalyst is in the form of an extrudate, most preferably a trilobal extrudate.

The catalysts described herein can also be used in the hydrogenolysis of polyols, especially in the conversion of glycerol to propylene glycol. Hydrogenolysis can be performed in liquid or vapor phase.

Method of Manufacture The catalysts described herein can be prepared according to the second aspect (sequential impregnation; Cu salt followed by Zn salt), the third aspect (sequential impregnation; Zn salt followed by Cu salt), or the fourth aspect (Zn salt followed by Cu salt). and Cu salt co-impregnation) method of preparation.

Impregnation techniques will be familiar to those skilled in the art. Generally, impregnation involves preparing an impregnation solution comprising the salt(s) to be impregnated and adding a volume of the impregnation solution to the support, wherein the volume of the impregnation solution is approximately equal to the absorption volume of the support.

The choice of copper salt is not particularly limited. A preferred copper salt is copper carbonate, which can be provided for impregnation as a solution of copper carbonate in ammonium hydroxide.

The choice of zinc salt is not particularly limited. A preferred zinc salt is zinc carbonate, which may be provided for impregnation as a solution of zinc carbonate in ammonium hydroxide.

Preferably, one or both of the copper salt and/or the zinc salt are nitrates.

A drying step is performed between impregnations. Typical drying conditions are 120°C ± 20°C for 4 h ± 2 h. A skilled person will readily be able to determine drying conditions, which may vary depending on the scale and equipment used.

Once all of the desired metal(s) are impregnated onto the support, the calcination step proceeds. Typical calcination conditions are 200 to 800 °C for 2 h ± 1 h. The skilled person will readily be able to determine the calcination conditions, which may vary depending on the scale and equipment used. In the case of sequential impregnations of different metal salts (second and third aspects), the drying step is carried out between the impregnation steps. A calcination step can also be performed between impregnation steps, but is not required.

Where nitrates are used, preferably any calcination step after impregnation with nitrates is carried out at a temperature not exceeding 350°C. For example, calcination may be performed at 300°C (eg, 300°C ± 50°C) for 2 h ± 1 h, such as at 300°C ± 25°C for 2 h ± 1 h. Under these relatively mild calcination conditions, residual nitrate remains after calcination and unexpectedly provides a selectivity benefit.

Hydrogenation Process The catalysts described herein are particularly suitable for the conversion of aldehydes to the corresponding alcohols, particularly in the liquid phase. Preferred aldehyde substrates include _C2 - _C20 aldehydes, which may be linear, branched or cyclic. In a preferred embodiment, the aldehyde is a C4-C20 linear, branched or cyclic aldehyde, such as a C1-C10 linear, branched or cyclic aldehyde. Exemplary substrates are: butyraldehyde (product butanol), 2-ethyl-3-propylacrolein (product 2-ethyl-hexan-1-ol), 2-propyl-3-butylacrolein (product 2-propyl-heptan-1-ol) and isononanal (product isononanol). A particularly preferred substrate is butyraldehyde.

EXAMPLES The invention will now be illustrated by the following non-limiting examples.

Comparative catalyst 1 (C1) is a commercially available catalyst sold for the conversion of butyraldehyde to butanol. It comprised approximately 20 wt% CuO on a 2.5 mm gamma-alumina trilobal support. The content of other metal oxides except CuO and Al ₂ O ₃ is <1% by weight.

C1 had a nitrogen content of 208 ppm as measured by CHN analysis.

General Procedure for CHN Analysis Catalyst samples were injected into a high temperature (900°C) pyrolysis tube with argon carrier gas. After the nitrogen compounds in the sample are pyrolyzed, they are combusted, oxidized and converted into nitrogen oxides (NO). After removing moisture from the combustion gas by a dehumidifier (tubular dryer), the following oxidation reaction occurs by the reaction of NO and ozone. NO + O ₃ → NO ₂ + O ₂ + hv

By this reaction, light with a wavelength of 590 to 2,500 nm is generated. The optical intensity of this light is proportional to the NO concentration over a broad frequency range. After detection of the emitted light by photomultiplier tubes and signal processing, area values are obtained. Using the area versus concentration relationship (calibration curve) obtained from the standard solutions, the total nitrogen concentration in the sample was calculated.

General procedure for the manufacture of doped catalysts The impregnation solution of the dopant is obtained by dissolving the necessary salt (cerium nitrate hexahydrate, iron nitrate nonahydrate or zinc nitrate hexahydrate) in an amount equal to the support to be impregnated Prepared with a quantity of demineralized water equal to the pore volume. The amount of metal nitrate added was that required to achieve a metal loading of 5% by weight, assuming complete absorption of the impregnating solution by the support.

The impregnation solution of ammonium cupric carbonate was prepared by dissolving ammonium carbonate and copper carbonate at about 1:1 w/w in ammonium hydroxide solution. The concentration of Cu in the impregnation solution was about 150 g/L.

Catalysts E2 to E4 were prepared by a sequential impregnation route. First, 2.5 mm trilobal gamma alumina was impregnated with a solution containing a dopant (Ce, Fe or Zn). The impregnated samples were dried using a muffle furnace. The sample was heated to 120°C and held at this temperature for 4 hours, then heated to the calcination temperature (300°C) and held at this temperature for 2 hours. A ramp rate of 5°C/min was used throughout. The samples were then allowed to cool to room temperature.

To achieve the target 20 wt% CuO in the final catalyst, impregnation with ammonium cupric carbonate solution via two sequential additions was necessary. The doped material prepared from the first step is impregnated with an impregnation solution comprising ammonium cupric carbonate. The impregnating solution was gradually added to the support until the appearance was tacky, consistent with 100% absorption. The material was then dried at 120°C for 4 hours and then allowed to cool to room temperature. This material is then impregnated with the remaining impregnation solution. The resulting material was dried in a muffle furnace by heating to 120°C at a ramp rate of 5°C/min and holding at this temperature for 2 hours, followed by heating to calcination temperature (300°C) and holding at this temperature 2 hours. A ramp rate of 5°C/min was used throughout. The samples were then allowed to cool to room temperature. Dopant loading (wt% oxide) CuO loading (wt%) Rest (wt%) Calcination temperature E2 _4.10 ( _Ce2O3 ) 21.45 74.45 300℃ E3 _5.50 ( _Fe2O3 ) 20.84 73.66 300℃ E4 4.62 (ZnO) 21.13 74.25 300℃

E2, E3, and E4 each had a total nitrogen content of 1326 ppm, 1416 ppm, and 2018 ppm, as measured by CHN analysis.

General Procedure for Catalyst Testing Glass wool was added to the bottom of the reactor followed by a portion of glass beads. Add more glass wool to the above, followed by about 20 ml of coarse SiC (0.5 to 1.1 mm) and then fine enough SiC (0.1 to 0.3 mm) to reach the bottom of the oil jacket. The catalyst bed was then loaded on top of fine SiC in five individual alternating aliquots of catalyst and SiC (cat/SiC/cat/SiC/cat/SiC/cat/SiC/cat/SiC). The total amount of SiC used was 45 g and the total amount of catalyst used was 15 g. An additional 60 ml of fine SiC was added on top of the catalyst bed, followed by a subsequent layer of 60 ml of coarse SiC, after which glass beads were added to fill the reactor tube.

The reactor was pressure tested to 25 barg with reducing gas and then hydrogen with no leaks detected (a leak exists if >1% of pressure is lost over a 30 minute period after isolation of the reactor). The flow rate of 5% hydrogen in nitrogen was then set at 0.5 L/min at a pressure of 0.6 barg.

The catalyst was heated to 240° C. at a rate of 1° C./min in 0.5 L/min flow rate of 0.5 L/min in nitrogen containing 5% hydrogen at 0.6 barg and maintained at these conditions for 4 hours, after which the reactor was lowered to to 140°C and start the catalyst test procedure to activate. The temperature is controlled by the oil jacket temperature and the catalyst in the reactor is assumed to be isothermal.

Example 1 - Accelerated Aging The gas was changed to 100% hydrogen and metered into the device at 0.33 L/min. The liquid feed (butyraldehyde >98% from Alfa Aesar) was gradually brought online in increments of 0.25 ml/min to achieve a rate of 1 ml/min. After each increment, the catalyst bed temperature was allowed to stabilize before increasing the liquid flow rate. The ratio of 0.33 L/min hydrogen and 1.0 ml/min pure butyraldehyde equals a 1.32:1 molar ratio of H ₂ :butyraldehyde and an LHSV of 4.0 hr ⁻¹ . The reactor jacket temperature was maintained at 140°C. These conditions were maintained for 3 days, during which on-line sampling was done.

The results are shown in Figure 1. Doped samples E2 to E4 each exhibited slower deactivation rates when compared to comparative (undoped) catalyst C1.

The LHSV used in these examples is much higher than that used in the commercial butyraldehyde to butanol process. The purpose of this test is to accelerate the catalyst priming cycle and determine the deactivation characteristics of the catalyst.

Example 2 - Effect of Reaction Temperature A commercial butyraldehyde to butanol process is typically operated adiabatically, with sections of the bed reaching temperatures of up to 170°C. The activity/selectivity of catalysts C1 and E2 to E4 was measured by varying the temperature of the reactor jacket across the relevant temperature range. Reducing the flow rates of hydrogen and butyraldehyde to 0.12 L/min and 0.375 ml/min, respectively, resulted in an LHSV of 1.5 hr ⁻¹ , but retained the H ₂ :butyraldehyde ratio of 1.32:1. The jacket temperature was increased and allowed to stabilize for about 4 hours at the following temperatures, where on-line analysis of the product was done at each temperature: 140, 150, 160 and 170°C.

The results are shown in Figure 2. Doped samples E2 to E4 each showed higher activity across the temperature range when compared to the comparative (undoped) catalyst C1. The catalyst doped with Zn had the lowest deactivation rate and the highest activity and was taken for further study.

Example 3 - Effect of Calcination Temperature A catalyst was prepared following the same method used to produce E4, except that the calcination temperature was 700°C instead of 300°C. ZnO loading weight % CuO loading weight% remaining weight% Calcination temperature Acetal in the product at 160°C (wt%) E4 4.62 21.13 74.25 300°C 0.4 E5 4.62 21.13 74.25 700°C 3

Catalyst E5 was tested against E4 under comparable conditions. The feed was >98% butyraldehyde, the LHSV was 1.5 hr ⁻¹ , the reactor temperature was 160° C. and the H ₂ :butyraldehyde ratio was 1.32:1. The acetal content of the product of E5 was significantly higher.

Example 4 - Effect of Calcination Conditions and Presence of Nitrate Note that the presence of residual nitrate was detectable by TGA-MS in catalyst E4 but not in E5 calcined at higher temperature. The presence of nitrate is thought to be the reason for the difference seen in selectivity.

To test this, a series of nitrate-free catalysts (E6 to E10) were prepared. These were prepared by a common impregnation approach using an impregnation solution prepared by dissolving copper carbonate and zinc carbonate in ammonium hydroxide solution. The choice of salt means that the solution does not contain any nitrates. The total CuO+ZnO content was kept constant at about 20% by weight, but with variations in CuO and ZnO content. The calcination temperature was also varied. These catalysts were tested for butyraldehyde to butanol conversion under the same conditions as Examples 2 and 3 (LHSV 1.5 hr ⁻¹ ). ZnO loading weight% CuO loading weight% remaining weight % Calcination temperature Acetal in the product at 160°C (wt%) E4* 4.62 21.13 74.25 300°C 0.4 E5 4.62 21.13 74.25 700°C 3 E6 10.41 10.34 79.25 300°C 1.2 E7 10.64 10.56 78.80 700°C 2.1 E8 7.14 14.46 78.40 478°C 1.7 E9 2.15 18.90 78.95 300°C 0.8 E10 2.23 18.41 79.36 566°C 1.5 *residual nitrates present

In general, lower calcination temperatures yielded lower % acetal by-products. E4 achieves the lowest content of acetal by-products, the only instance where nitrates can be detected in the calcined catalyst.

Example 5 - Use of Feedstock with Lower Butyraldehyde Content The feedstock used in Examples 1 to 4 was >98% butyraldehyde. Trials were performed on a feedstock more representative of a commercial process (butanol containing about 15% butyraldehyde). The LHSV was 1.5 hr ⁻¹ , the reactor temperature was 140° C. and the H ₂ :butyraldehyde ratio was 1.32:1.

The results are shown in Figure 3a. E4 showed higher butyraldehyde conversion and slower deactivation rate compared to C1. "Feed Change" shows that the content of butyraldehyde in the feed decreased from 18.5% to 14.5%.

The main by-products of the reaction under the conditions of Example 5 were acetal trimer "acetal", n-butyl butyrate and other unknown substances. Figure 3b shows that E4 produces significantly less acetal by-products than C1. Figures 3c and 3d show that the amounts of n-butyl butyrate and unknowns are similar between E4 and C1.

In conclusion, about 20% by weight CuO and about 5% by weight ZnO on an alumina catalyst provides a catalyst that is more active after reduction than a comparable catalyst without ZnO doping, less prone to deactivation, and Produces fewer by-products.

Aspects of the present invention 1. An oxidation catalyst comprising zinc and copper on an Al ₂ O ₃ support, wherein the oxidation catalyst comprises: 1 to 15% by weight ZnO; and 5 to 30% by weight CuO; in each case The following is based on the total weight of the oxidation catalyst; wherein ZnO, CuO and Al ₂ O ₃ together constitute ≥ 95% by weight of the oxidation catalyst.

2. The oxidation catalyst of aspect 1, wherein the oxidation catalyst comprises >250 ppm nitrogen, as measured by CHN analysis.

3. The oxidation catalyst of aspect 1 or aspect 2, wherein ZnO, CuO and Al ₂ O ₃ together constitute ≥ 98% by weight of the oxidation catalyst.

4. The oxidation catalyst of any one of aspects 1 to 3, wherein the oxidation catalyst is in the form of granules, pellets or extrudates.

5. The oxidation catalyst of any one of aspects 1 to 3, wherein the oxidation catalyst is in the form of a trilobal extrudate.

6. The oxidation catalyst of aspect 1, wherein the oxidation catalyst comprises: 5 to 12.5% by weight ZnO; 15 to 25% by weight CuO; in each case based on the total weight of the oxidation catalyst; wherein ZnO, CuO and Al ₂ O ₃ together constitute ≥ 95% by weight of the oxidation catalyst.

7. The oxidation catalyst of aspect 6, wherein the oxidation catalyst is in the form of a trilobal extrudate.

8. A method for producing an oxidation catalyst, comprising the following steps: (i) impregnating the alumina support with an impregnation solution comprising a copper salt; (ii) drying and optionally calcining the product of step (i); (iii) impregnating the product of step (ii) with an impregnation solution comprising a zinc salt; (iv) drying and calcining the product of step (iii); Wherein the oxidation catalyst produced after step (iv) is the catalyst according to any one of aspects 1 to 7.

9. A method for producing an oxidation catalyst, comprising the following steps: (i) impregnating the alumina support with an impregnation solution comprising a zinc salt; (ii) drying and optionally calcining the product of step (i); (iii) impregnating the product of step (ii) with an impregnation solution comprising a copper salt; (iv) drying and calcining the product of step (iii); Wherein the oxidation catalyst produced after step (iv) is the catalyst according to any one of aspects 1 to 7.

10. A method for producing an oxidation catalyst, comprising the following steps: (i) impregnating the alumina support with an impregnating solution comprising a copper salt and a zinc salt; (ii) drying and calcining the product of step (i); Wherein the oxidation catalyst produced after step (ii) is the catalyst according to any one of aspects 1 to 7.

11. The method of any one of aspects 8 to 10, wherein the temperature during any calcining step does not exceed 350°C.

12. The method of any one of aspects 8 to 11, wherein the alumina support is in the form of granules, pellets or extrudates.

13. The method of any one of aspects 8 to 12, wherein the alumina support is in the form of a trilobal extrudate.

14. The method of any one of aspects 8 to 13, comprising the additional step of reducing the oxidation catalyst to produce a reduction catalyst.

15. A reducing catalyst obtained or obtainable by the method of aspect 14.

16. A method for converting aldehydes into corresponding alcohols using a catalyst, wherein the catalyst according to aspect 15 is used as the catalyst.

17. The method of aspect 16, wherein the aldehyde is a C4-20 aldehyde.

18. The method of aspect 16, wherein the aldehyde is a C4-10 aldehyde.

19. The method of any one of aspects 16 to 18, wherein the aldehyde is an α,β-unsaturated aldehyde.

20. The method of aspect 16, wherein the aldehyde is butyraldehyde.

21. The method of aspect 16, wherein the aldehyde is 2-ethyl-3-propylacrolein.

22. The method of aspect 16, wherein the aldehyde is 2-propyl-3-butylacrolein.

23. The method of aspect 16, wherein the aldehyde is isononanal.

24. The method of any one of aspects 16 to 23, wherein the method is carried out in the liquid phase.

Figure 1 shows the conversion of butyraldehyde as a function of on-line time under the conditions of WHSV = 4.0 h ^-1 and T = 140°C.

Figure 2 shows the conversion of butyraldehyde as a function of jacket temperature at WHSV = 1.5 h ⁻¹ .

Figure 3a shows the conversion of butyraldehyde as a function of on-line time at WHSV = 1.5 h ^-1 and T = 140°C with a feed of butanol containing about 15% butyraldehyde.

Figure 3b shows the fraction of acetal by-product as a function of online time with a feed of butanol containing about 15% butyraldehyde at WHSV = 1.5 h ^-1 and T = 140°C.

Figure 3c shows the proportion of 2-butyl butyrate as a function of online time at WHSV = 1.5 h ^-1 and T = 140°C with a feed of butanol containing about 15% butyraldehyde.

Figure 3d shows the proportion of unknowns as a function of on-line time at WHSV = 1.5 h ^-1 and T = 140°C with a feed of butanol containing about 15% butyraldehyde.

Claims (15)

A method for converting aldehydes into corresponding alcohols using a reduction catalyst, wherein the reduction catalyst is formed by reducing _an oxidation catalyst comprising zinc and copper on an _Al2O3 support, wherein the oxidation catalyst The medium comprises: 1 to 15% by weight ZnO; and 5 to 30% _by weight CuO; in each case based on the total weight of the oxidation catalyst; wherein ZnO, CuO and _Al2O3 together constitute ≥ 95% of the oxidation catalyst weight%. The method of claim 1, wherein the oxidation catalyst comprises >250 ppm nitrogen, as measured by CHN analysis. The method of claim 1 or claim 2, wherein ZnO, CuO and Al ₂ O ₃ together form ≥ 98% by weight of the oxidation catalyst. The method according to any one of claims 1 to 3, wherein the oxidation catalyst is in the form of granules, pellets or extrudates. A method according to any one of claims 1 to 3, wherein the oxidation catalyst is in the form of a trilobal extrudate. The method of claim 1, wherein the oxidation catalyst comprises: 5 to 12.5% by weight ZnO; 15 to 25% by weight CuO; in each case based on the total weight of the oxidation catalyst; wherein ZnO, CuO and Al ₂ O ₃ together constitute ≥ 95% by weight of the oxidation catalyst. The method of claim 6, wherein the oxidation catalyst is in the form of a trilobal extrudate. The method according to any one of claims 1 to 7, wherein the aldehyde is a C4-20 aldehyde. The method of claim 8, wherein the aldehyde is a C4-10 aldehyde. The method according to any one of the above claims, wherein the aldehyde is an α,β-unsaturated aldehyde. The method of claim 8 or claim 9, wherein the aldehyde is butyraldehyde. The method according to claim 10, wherein the aldehyde is 2-ethyl-3-propylacrolein. The method according to claim 10, wherein the aldehyde is 2-propyl-3-butylacrolein. The method according to claim 8 or claim 9, wherein the aldehyde is isononyl aldehyde. The method according to any one of the above claims, wherein the method is carried out in liquid phase.

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