Catalyst support comprising homogeneously distributed titanium dioxide and method for production

Abstract

The present invention relates a method of making a catalyst support comprising at least homogeneously distributed titanium dioxide and alumina and to a catalyst support obtained according to this method.

Claims

1. A method of preparing a catalyst support, the method comprising the following steps: i) preparing an alumina suspension, the alumina suspension having a pH of between 6 and 8, wherein the alumina suspension comprises an alumina selected from the group consisting of transition alumina, boehmite and mixtures thereof; ii) preparing a titanium compound solution; iii) adding an acid to the alumina suspension until the pH of the alumina suspension is between 4 and 5 to form an acid modified alumina suspension; iv) adding the titanium compound solution to the acid modified alumina suspension to form an alumina/titanium compound suspension; and v) drying and calcining the alumina/titanium compound suspension to form the catalyst support.

2. The method according to claim 1 comprising the further step of adding an acid to the alumina/titanium compound suspension.

3. The method according to claim 2 comprising the further step of heating the alumina/titanium compound suspension.

4. The method according to claim 1 comprising the further step of drying the acid modified alumina suspension before adding the titanium compound solution.

5. The method according to claim 4, wherein the acid added is a carboxylic acid selected from the group consisting of formic acid, lactic acid, citric acid, and mixtures thereof.

6. The method according to claim 1, wherein the acid added to the alumina suspension is formic acid, lactic acid, citric acid, or mixtures thereof.

7. The method of claim 1, wherein the alumina/titanium compound suspension comprises 99 to 95 wt. % alumina, calculated as Al.sub.2O.sub.3, and 1 to 5 wt. % titanium compounds, calculated as TiO.sub.2, relative to sum of alumina, calculated as Al.sub.2O.sub.3, and titanium compounds, calculated as TiO.sub.2.

8. The method of claim 1, wherein the percentage of acid added to the alumina suspension is between 5 to 30 wt % of the acid modified alumina suspension.

9. The method according to claim 1, wherein the transition alumina is γ-alumina, δ-alumina, θ-alumina or mixtures thereof.

10. The method according to claim 1, wherein the titanium compound solution is made by dissolving a titanium precursor in at least water.

11. The method according to claim 10, wherein the titanium precursor is a water-soluble titanium precursor selected from the group consisting of potassium titanium oxalates, ammonium titanium oxalates, ammonium titanium lactates, and mixtures thereof.

12. A method of preparing a promoted catalyst support, the method comprising: i) preparing a catalyst support according to claim 1, and ii) introducing a promoter onto and/or into the catalyst support thereby to obtain a promoted catalyst support.

13. The method according to claim 1 comprising the further step of heating the alumina/titanium compound suspension.

14. A calcined catalyst support comprising an alumina support coated with between 1 and 5 wt. % TiO.sub.2 in relation to the alumina support (Al.sub.2O.sub.3), the TiO2 being homogeneously dispersed on the alumina support.

Description

(1) The invention will now be described in more detail with reference to the accompanying drawings and the following non-limiting examples where:

(2) FIG. 1 is a cross-sectional SEM image of Comparative Example 3 wherein white spots represent TiO.sub.2 enrichment; and

(3) FIG. 2 is a cross-sectional SEM of Example 3.

EXPERIMENTAL

(4) The titanium(IV) bis(ammonium lactato) dihydroxide (TALH) used is a 1 wt % aqueous solution of TALH known in the trade as Tyzor® LA (calculated as TiO.sub.2).

(5) In the examples below the wt % of Ti calculated as TiO.sub.2 in the catalyst support is expressed in terms of the total weight of the catalyst support.

(6) X-ray photoelectron spectroscopy (XPS) was used in the examples below to determine the TiO.sub.2 distribution on the alumina surface. XPS is a surface-sensitive quantitative spectroscopic technique that measures the elemental composition at the parts per thousand parts range. Since XPS is only surface sensitive, the samples were analysed by XPS both as received (particle as is) and after being ground (crushed) using a pestle and mortar and the ratios of elements were reported. Approximately the same amount of sample was used for the grinding step (compared to the samples where the particles as is were measured) using a pestle and mortar with only just enough force being applied to break down the particles.

(7) The XPS spectra were recorded on the KRATOS Axis Ultra DLD, with the analyser operating at the fixed pass energy of 160 eV for the survey spectrum and 20 eV for the individual regions. The measurements were carried out using the Al Kα monochromated source. Due to the nature of the materials, neutralisation was necessary during the acquisition. All the spectra were corrected in energy using the C 1s at 284.6 eV. All the samples were mounted as loose powders in a molybdenum sample holder. The peak area ratios as determined by XPS for all the support samples in the Examples are provided in Tables 1, 2, and 3 together with the calculated difference between the particle as is and the crushed sample. The larger this difference the less homogeneous is the sample. Homogeneous samples show very small or even negative values.

Examples—Options 1 and 2 of the First Aspect of the Invention

(8) As described hereinbefore options 1 and 2 of the first aspect of the invention do not include the step of drying the acid modified alumina suspension before addition of the titanium compound solution (known as Equilibrium Deposition Filtration (hereinafter “EDF”)).

Comparative Example 1: TALH Equilibrium Deposition Filtration (Hereinafter “EDF”) with No Acid Addition

(9) 38.8 g Puralox SCCa-150 was suspended in 46.5 g water to obtain a 45.5 wt % Al.sub.2O.sub.3 in water suspension. 164 g of a TALH aqueous solution (1 wt-% TiO.sub.2) was added to the alumina suspension and heated for 3 hours at 50° C., filtered, dried and calcined at 550° C. The resulting modified support included 1.1 wt % TiO.sub.2 (based on the total weight of the modified support).

Comparative Example 2—Same Process as Described in WO 2013/114098 A1: 1 Step TALH EDF with Citric Acid—Premix

(10) 38.6 g Puralox SCCa-150 was suspended in 46 g water (45.5 wt % suspension). 160 g of a mixed solution of TALH and citric acid was added to the suspension (1 wt % TiO.sub.2=11 g TALH, 20 wt % citric acid related to the amount of TALH used=2.2 g). The mixture was heated, stirred at 50° C. for 3 h, filtered, dried and calcined at 550° C. The resulting modified support included 1.7 wt % TiO.sub.2 (based on the total weight of the modified support).

Example 1: TALH EDF with Citric Acid (AP15-171)

(11) 38.8 g Puralox SCCa-150 was suspended in 46.5 g water to obtain a 45.5 wt % Al.sub.2O.sub.3 in water suspension. 11.2 g of 40 wt-% citric acid solution was added to the suspension to adjust the pH of the suspension to a pH of 4 producing an acid modified alumina suspension. 164 g of a 1 wt-% TiO.sub.2 aqueous TALH solution was then added to the acid modified alumina suspension and the alumina/titanium compound suspension was heated for 3 h at 50° C. under a pH control of 4 using citric acid, filtered, dried and calcined at 550° C. The resulting catalyst support included 2.2 wt % TiO.sub.2 (based on the total weight of the modified support).

(12) The Examples show that the addition of an acid to the alumina suspension before the addition of the Ti compound results in a much higher TiO.sub.2 adsorption on the alumina when compared to no acid treatment or to premixing of the acid with the Titania (TiO.sub.2) as per Comparative Examples 1 and 2.

(13) The Ti:Al ratios for the particle as is and the ground (crushed) sample of the catalyst support as prepared in Example 1 are found to be nearly the same and therefore the titania surface distribution is considered to be homogeneous across the inner and outer surface of the support particle. Functionalising the alumina support with an acid, in this case citric acid prior to TALH EDF impregnation as in Example 1 resulted in a homogenous Ti distribution (see Table 1, Example 1 XPS Ti:Al peak ratios) compared to Comparative Example 2 where the titanium compound and carboxylic acid were contacted with the catalyst support at the same time without prior treatment of the catalyst support material with an acid where an inhomogeneous Ti distribution was obtained.

(14) The support modification results demonstrate that the improvement in adsorption is a function of pH as well as the fact that the surface of the alumina is functionalised by the acid.

(15) The results are included in Table 1 hereunder:

(16) TABLE-US-00001 TABLE 1 XPS and ICP analysis of TALH EDF impregnation XPS peak area TiO.sub.2 ratio of Ti:Al* Difference between (wt.-%), Target particle crushed particle as is and Distribution Example TiO.sub.2 = 4.1 as is sample crushed sample XPS Comparative 1.1 0.2365 0.0184 0.2181 inhomogeneous Example 1 Comparative 1.7 0.0502 0.0165 0.0337 Inhomogeneous Example 2 Example 1 2.2 0.0264 0.0197 0.0067 homogeneous

Examples—Options 3 and 4 of the First Aspect of the Invention

(17) As described hereinbefore options 3 and 4 of the first aspect of the invention include the step of drying the acid modified alumina suspension before addition of the titanium compound solution (known as Incipient Wetness hereinafter “IW”)).

Comparative Example 3: TALH, IW with No Acid Addition

(18) 13.7 g TALH was dissolved in water to obtain a resultant 21 mL aqueous TALH solution. The TALH solution was then added dropwise to a 54.4 g Puralox SCCa-2/150 suspension during intensive mixing. The water was removed under atmospheric pressure at 80° C. and calcined at 550° C. for 3 hours. The resulting catalyst support included 4.1 wt % TiO.sub.2, but the TiO.sub.2 distribution was inhomogeneous (see Table 2 and FIG. 1).

Comparative Example 4: 1-Step TALH IW with 20 wt-% Citric Acid (Expressed in Relation to TALH) (Premixing)

(19) 11.3 g TALH was dissolved in water to obtain a resultant 18 mL aqueous TALH solution. 2.3 g citric acid was added to the TALH solution as a solid. This solution was added to a 38.8 g Puralox SCCa-2/150 suspension under intensive mixing. The water was removed under atmospheric pressure at 80° C. and calcined at 550° C. for 3 hours. The resulting catalyst support had an inhomogeneous distribution of TiO.sub.2.

Example 2: 2-Step: 20 wt-% Citric Acid, Drying, TALH IW

(20) 18 mL of a 20 wt.-% citric acid solution was added to 38.8 g Puralox SCCa-2/150 suspension and allowed to mix. The mixture was dried at 80° C. under atmospheric pressure. 11.3 g TALH was dissolved in water to obtain an 18 mL aqueous TALH solution. This solution was added to the dried acid-modified Puralox mixture to form an alumina/titanium compound suspension. This alumina/titania compound suspension is then dried at 80° C. to remove the water and calcined at 550° C. for 3 hours to obtain a catalyst support including 4.1 wt % TiO.sub.2 with a homogeneous TiO.sub.2 dispersion.

Example 3—2-Step: 5 wt-% Citric Acid, Drying, TALH IW

(21) A modified alumina support with 4.1 wt % TiO.sub.2 was prepared as described in Example 2, however, the Puralox was treated with a 5 wt.-% citric acid solution. The homogeneity of the dispersed TiO.sub.2 on the modified support was good as per Table 2 and FIG. 2.

Example 4: 2-Step: 10 wt-% Lactic Acid, Drying, TALH IW

(22) To 29.2 g Puralox SCCa-150 suspension, 14 mL of a 10 wt.-% lactic acid solution was added and allowed to mix. The mixture was dried at 80° C. under atmospheric pressure. 8.5 g TALH was dissolved in water to obtain a 14 mL aqueous TALH solution. This was added to the dried acid-treated Puralox mixture to form an alumina/titanium compound suspension. The alumina/titanium compound suspension was then dried at 80° C. to remove the water and calcined at 550° C. for 3 hours to obtain a catalyst support of 4.1 wt % TiO.sub.2 with a homogeneous Ti compound dispersion.

Example 5—2-Step: 5 wt-% Lactic Acid, Drying, TALH IW

(23) To 29.1 g Puralox SCCa-150 suspension, 13 mL of a 5 wt.-% lactic acid solution was added and allowed to mix. The mixture was dried at 80° C. under atmospheric pressure. 8.5 g TALH was dissolved in water to obtain a 13 mL aqueous TALH solution. This was added to the dried acid-treated Puralox mixture as prepared in the 1st step to form an alumina/titanium compound suspension. The alumina/titanium compound suspension was dried at 80° C. to remove the water and calcined at 550° C. for 3 hours. The homogeneity of the dispersed TiO.sub.2 on the catalyst support was good.

(24) As per the examples and as outlined in Table 2 adding an acid to the alumina suspension prior to contacting the alumina suspension or mixture with the titanium compound (TALH), that is, a 2 step treatment process showed that the TiO.sub.2 adsorption can be significantly improved and the titania is uniformly distributed on the inner and outer surfaces of the alumina support.

(25) TABLE-US-00002 TABLE 2 XPS and ICP analysis of TALH IW impregnation: Difference XPS peak area between ratio of Ti:Al* particle as is TiO.sub.2 Particle crushed and crushed Distribution Example (wt.-%) as is sample sample XPS Comparative 4.1 0.3515 0.0321 0.3194 Inhomogeneous Example 3 Comparative 4.1 0.0596 0.0302 0.0294 Inhomogeneous Example 4 Example 2 4.1 0.0119 0.0294 −0.0175 Homogeneous Example 3 4.1 0.0192 0.0305 −0.0113 Homogeneous Example 4 4.1 0.0245 0.0300 −0.0055 Homogeneous Example 5 4.1 0.0392 0.0309 −0.0083 Homogeneous

Examples for the Fourth Aspect of the Invention

Mn Impregnation Examples

Comparative Example 5: TALH IW with No Acid Addition Pretreatment, MnAc IW

(26) A catalyst support was prepared as described in Comparative Example 3 but manganese acetate (MnAc) was added by incipient wetness after calcination.

(27) 26.9 g TALH was dissolved in water to obtain a resultant 42 mL aqueous TALH solution. This was added dropwise to 91, 8 g Puralox SCCa-150 and allowed to mix with a Krups stirrer. The water was removed under atmospheric pressure at 120° C. and calcined at 550° C. for 3 hours. 12, 5 g manganese acetate tetrahydrate (Mn (CH.sub.3COO).sub.2.4H2O) was dissolved in 42 mL water and added dropwise to the calcined powder. The catalyst support was dried at 120° C. and calcined again for 3 h at 550° C. to obtain a catalyst comprising of 3.9 wt % TiO.sub.2 and 4.7 wt % MnO.sub.2.

Comparative Example 6: 1 Step TALH IW with 20 wt-% Citric Acid, MnAc IW

(28) A catalyst support was prepared as described in Comparative Example 4 but with the addition of manganese acetate (MnAc) in a second incipient wetness step after drying.

(29) 22.8 g TALH was dissolved in water to obtain a resultant 36 mL aqueous TALH solution. 4.6 g citric acid was added to the TALH solution as a solid. This solution was added dropwise to 78 g Puralox SCCa-2/150 while mixing with a Krups stirrer. The water was removed under atmospheric pressure at 120° C. 10.6 g manganese acetate tetrahydrate was dissolved in 36 mL water and added dropwise to this dried powder, dried at 120° C. at atmospheric pressure and calcined for 3 h at 550° C. in air. The modified support comprised of 3.9 wt % TiO.sub.2 and 4.7 wt % MnO.sub.2

Comparative Example 7: 1 Step TALH IW, MnAc IW with 20 wt-% Citric Acid

(30) A catalyst support was prepared as described in Comparative Example 4 but with MnAc addition during the TALH-citric acid-IW:

(31) 22.8 g TALH, 10.6 g manganese acetate tetrahydrate and 4.6 g citric acid were dissolved in water to obtain a resultant 36 mL aqueous solution. This solution was added dropwise to 78 g Puralox SCCa-2/150 while mixing with a Krups stirrer. The water was removed under atmospheric pressure at 120° C. and the powder was calcined for 3 h at 550° C. in air. The modified support comprised of 3.9 wt % TiO.sub.2 and 4.7 wt % MnO.sub.2.

Example 6: 2-Step: TALH and MnAc IW with 5 wt-% Citric Acid Pretreatment

(32) A catalyst support was prepared as described in Example 3 but with MnAc addition during the TALH-citric acid-incipient wetness:

(33) To 73.9 g Puralox SCCa-2/150 34 mL, 5 wt.-% citric acid solution was added and allowed to mix. The mixture was dried at 80° C. under atmospheric pressure. 21.5 g TALH and 10 g manganese(II)acetate tetrahydrate (Mn(CH.sub.3COO).sub.2.4H.sub.2O) was dissolved in water to obtain a 34 mL aqueous TALH/Mn acetate solution.

(34) To the dried acid-treated Puralox, as prepared in the 1.sup.st step, the aqueous TALH/MnAc solution was added in a 2.sup.nd step impregnation, dried at 80° C. to remove the water and calcined at 550° C. for 3 hours to obtain a modified support of 4.1 wt % TiO.sub.2 and 4.7 wt % MnO.sub.2. Drying was performed at 80° C. to prevent large acid losses during drying.

Example 7: 2-Step: TALH EDF, 5 wt-% Citric Acid and Mn Acetate IW

(35) A catalyst support was prepared as described in Example 1 but with MnAc addition by incipient wetness after calcination:

(36) An Al.sub.2O.sub.3 in water suspension was prepared by mixing 85.8 g Puralox SCCa-2/150 with 102 mL water, the suspension was adjusted to pH 4 by a 40 wt % citric acid solution. 950 g of a 1 wt-% TiO.sub.2 aqueous TALH solution was thereafter added to the suspension and heated to 50° C. for 3 hours under a pH control of 4 using citric acid. The suspension was filtered, dried and calcined at 550° C. After calcination, 12.4 g manganese acetate tetrahydrate was dissolved in 43 mL water and added dropwise to the powder, dried at 120° C. and calcined 3 hours at 550° C.

(37) The XPS peak ratio results for Comparative Example 5 and Example 6 are included in Table 3 for the Ti and Mn modified sample prepared via the incipient wetness route show that the titania is predominantly located on the inner surfaces of the supports while the manganese is uniformly located on the inner and outer surfaces of the support.

(38) The Results are included in Table 3 hereunder:

(39) TABLE-US-00003 TABLE 3 XPS and ICP anaysis of Mn(CH.sub.3COO).sub.2•4H.sub.2O IW impregnation Difference XPS peak area between XPS peak Mn:Al for particle as is area ratio the crushed and crushed MnO.sub.2 Example of Mn:Al sample sample (wt.-%) Comparative 0.1712 0.0640 0.1072 4.5 Example 5 Example 6 0.0399 0.0459 −0.006 4.4