NEW HETEROGENEOUS PALLADIUM-BASED CATALYST, PREPARATION METHOD AND USE THEREOF

Abstract

A new catalyst that includes palladium on a cerium dioxide support, of formula PdX/CeO2, in which X represents the empty set or a doping element, and its use in the implementation of a method for selectively preparing oxalates or oxamides from carbon monoxide, an oxidant, in particular molecular oxygen or air, and an alcohol or an amine respectively.

Claims

1-23. (canceled)

24. A method for selectively preparing an oxalate compound or an oxamide compound comprising a step A of bringing an alcohol or an amine, respectively, into contact with: carbon monoxide, an oxidizing agent, a catalyst of formula PdX/CeO.sub.2, wherein X represents an empty set or a dopant element, comprising Pd atoms on a CeO.sub.2 support, in which the catalyst has a surface area, analyzed by BET, from 100 to 250 m/g,.sup.2 to obtain a reaction medium which may be pressurized from 0.1 to 15 MPa, and to obtain the oxalate compound or the oxamide compound.

25. The method for selectively preparing an oxalate compound or an oxamide compound according to claim 24, comprising a step A of bringing an alcohol or an amine, respectively, into contact with a promoter.

26. The method for selectively preparing an oxalate compound or an oxamide compound according to claim 24, comprising a step A of bringing an alcohol or an amine, respectively, into contact with a base.

27. The method for selectively preparing an oxalate compound or an oxamide compound according to claim 24, comprising a step A of bringing an alcohol or an amine, respectively, into contact with a solvent.

28. The method for selectively preparing an oxalate compound or an oxamide compound according to claim 24, further comprising a step B of heating the reaction medium.

29. The method for selectively preparing an oxalate compound or an oxamide compound according to claim 24, wherein the catalyst has a palladium content from 0.1 to 10%, in particular 2%, or 5%, by weight relative to the total weight of the catalyst.

30. The method for selectively preparing an oxalate compound or an oxamide compound according to claim 24, wherein a dopant is chosen from Mn, Mg, Ca, Fe, Ba, Sr, Y, Nb, Zn, Bi, Sn, La, Pr, Nb and Sm, in particular at a content from 0.5 to 10%, preferably 1%, by weight relative to the total weight of the catalyst.

31. The method for selectively preparing an oxalate compound or an oxamide compound according to claim 24, comprising a step A of bringing an alcohol or an amine, respectively, into contact with: carbon monoxide, in particular used from 0.5 to 8.0 MPa, in particular at 6.5 MPa oxygen or air, in particular oxygen used from 0.5 to 2.5 MPa, in particular at 1.5 MPa a promoter, in particular an iodine compound, chosen in particular from tetramethylammonium iodide, potassium iodide or sodium iodide, preferably tetramethylammonium iodide, preferably in a proportion from 0.1 to 5 mol % relative to the alcohol or amine, in particular in a proportion of 0.2 mol %, a PdX/CeO.sub.2 catalyst comprising Pd atoms on a CeO.sub.2 support of the formula PdX/CeO.sub.2 wherein X represents the void system or a dopant element, wherein the catalyst has a surface area, analyzed by BET, from 100 to 250 m.sup.2/g, preferably the palladium is from 0.01 to 10 mol % relative to the alcohol or amine, optionally a base, in particular triethylamine, preferably used in a proportion from 0.1 to 5 mol % relative to the alcohol or amine, in particular in a proportion of 0.15 mol %, optionally a solvent, in particular selected from acetonitrile, tetrahydrofuran, dioxane and toluene, preferably acetonitrile, to obtain a reaction medium, optionally a step B of heating the reaction medium, to obtain the oxalate compound or the oxamide compound.

32. The method for selectively preparing an oxalate compound or an oxamide compound according to claim 24, wherein an oxalate compound is selectively prepared, and wherein the method comprises a step A of bringing an alcohol into contact with: carbon monoxide, oxygen or air, a promoter, a PdX/CeO.sub.2 catalyst, comprising Pd atoms on a CeO.sub.2 support, of the formula PdX/CeO.sub.2 wherein X represents the void system or a dopant element, wherein the catalyst has a surface area, analyzed by BET, from 100 to 250 m.sup.2/g, preferably in an amount from 0.01 to 10 mol % relative to the alcohol or amine, to obtain a reaction medium, a step B of heating said reaction medium, in particular at a temperature from 25 to 200 C., in particular from 60 to 110 C., preferably around 90 C., to obtain the oxalate compound.

33. The method for selectively preparing an oxalate compound or an oxamide compound according to claim 32, wherein the method comprises a step A of bringing an alcohol, into contact with a base.

34. The method for selectively preparing an oxalate compound or an oxamide compound according to claim 32, wherein the method comprises a step A of bringing an alcohol, into contact with a solvent.

35. The method for selectively preparing an oxalate compound or an oxamide compound according to claim 24, wherein an oxalate compound of Formula 2 is selectively prepared, and wherein step A comprises contacting an alcohol of Formula 1: ##STR00005## wherein R.sub.a represents: a C.sub.1 to C.sub.20 linear or branched alkyl group, a C.sub.3 to C.sub.10 cycloalkyl group, a C.sub.5 to C.sub.20 alkyl-aryl or alkyl-heteroaryl group, in particular the alcohol is chosen from methanol, ethanol and isopropanol.

36. The method for selectively preparing an oxalate compound or an oxamide compound according to claim 24, wherein an oxamide compound is selectively prepared, and wherein the method comprises a step A of bringing an amine into contact with: carbon monoxide, oxygen or air, a promoter, a PdX/CeO.sub.2 catalyst comprising Pd atoms on a CeO.sub.2 support of the formula PdX/CeO.sub.2 wherein X represents the empty set or a dopant element, wherein the catalyst has a surface area, analyzed by BET, from 100 to 250 m.sup.2/g, preferably the palladium is from 0.01 to 10 mol % relative to the alcohol or amine, a solvent, to obtain a reaction medium comprising the oxamide compound.

37. The method for selectively preparing an oxalate compound or an oxamide compound according to claim 36, wherein an oxamide compound is selectively prepared, and wherein the method comprises a step A of bringing an amine, into contact with a base.

38. The method for selectively preparing an oxalate compound or an oxamide compound according to claim 36, wherein an oxamide compound of Formula 4 is selectively prepared, and wherein step A comprises contacting an amine of Formula 3: ##STR00006## wherein R.sub.b and R.sub.c independently of one another represent: a hydrogen atom, a C.sub.1 to C.sub.20 linear or branched alkyl group, a C.sub.3 to C.sub.10 cycloalkyl group, a C.sub.5 to C.sub.20 alkyl-aryl or alkyl-heteroaryl group, at least one of the groups R.sub.b or R.sub.c being other than hydrogen, R.sub.b and R.sub.c can form a cycle, in particular the amine is chosen from piperidine, pyrrolidine, butylamine, benzylamine, furfurylamine and cyclohexylamine.

39. A palladium/cerium dioxide catalyst, comprising palladium on a cerium dioxide support, of the formula PdX/CeO.sub.2, wherein X represents the void or a doping element, wherein the catalyst has a surface area, analyzed by BET, from 100 to 250 m.sup.2/g, in particular from 100 and 200 m.sup.2/g, and wherein the catalyst has a palladium content from 0.1 to 10%, in particular 2% or 5%, by weight relative to the total weight of the catalyst, optionally the dopant being selected from the following group of elements: Mn, Mg, Ca, Fe, Ba, Sr, Y, Nb, Zn, Bi, Sn, La, Pr, Nb and Sm, preferably the dopant being Mn, in particular the said catalyst comprising a dopant content from 0.5 and 10%, in particular 1%, by weight relative to the total weight of the catalyst.

40. The catalyst according to claim 39, wherein the catalyst has a fluorine-type structure by XRD and a crystallite size of less than 30 nanometers according to the Scherrer formula, in particular less than 20 nanometers, preferably less than 10 nanometers, or wherein the catalyst has a crystallinity level from 0 to 50%, preferably from 0 to 20%.

41. The catalyst according to claim 39, wherein said catalyst is in the form of particles of average micrometric size, in particular from 1 to 100 m.

42. The catalyst according to claim 39, wherein the surface of the said catalyst, analyzed by XPS, comprises from 90 to 100% palladium in the oxidation state (II), in particular in the form of PdO or a Pd.sub.xCe.sub.1-xO.sub.2 solid solution, x varying from 0.01 to 1.

43. A method for preparing a PdX/CeO.sub.2 catalyst according to claim 39, wherein the method comprises: a step D of impregnating a palladium salt, in particular palladium nitrate, on a cerium dioxide support, to obtain a homogeneous material, in particular said step D comprises: the use of a support with a surface area from 100 to 300 m.sup.2/g, in particular from 150 to 160 m.sup.2/g or from 270 to 280 m.sup.2/g, and using a palladium salt concentration calculated to obtain a palladium content of 0.1 to 10%, by weight relative to the total weight of the catalyst, optionally using another salt selected from precursors of dopants from the following group of elements: Mn, Mg, Ca, Fe, Ba, Sr, Y, Nb, Zn, Bi, Sn, La, Pr, Nb and Sm, in particular the manganese salt, the dopant salt concentration is calculated to obtain a dopant content from 0.5 to 10% by weight relative to the total weight of the catalyst, a step E for drying the material, in particular at a temperature from 60 to 100 C., in particular 80 C., preferably for a period from 10 to 24 hours, in particular 16 hours, and a step F of palladium activation, in particular comprising calcination at a temperature from 200 to 1000 C., in particular 600 C., preferably for a period from 1 to 15 hours, in particular 2 hours, to obtain said catalyst.

Description

FIGURES

[0561] FIG. 1 shows the diffractograms obtained from 10 to 90 degrees at 2, FIG. 1a) is an X-ray diffractogram of the HSA 20SP ceria support, FIG. 1b) is a diffractogram of the Pd (2%)/CeO.sub.2 catalyst (HSA 20 SP), FIG. 1c) is a diffractogram of the Pd (2%)Mn (1%)/CeO.sub.2 catalyst (HSA 20 SP).

[0562] FIG. 2 shows SEM images of the Pd (2%)/CeO.sub.2 catalyst (HSA 85 SP).

[0563] FIG. 3 shows SEM images of the Pd (2%)/CeO.sub.2 catalyst (HSA 20 SP).

[0564] FIG. 4 shows SEM images of the Pd (2%)Mn (1%)/CeO catalyst (HSA 20 SP).

[0565] FIG. 5 shows the spectra of the Pd (2%)/CeO.sub.2 catalyst (HSA 20 SP) at the binding energies corresponding to Pd 3d (FIG. 5a), Ce 3d (FIG. 5b) and O 1s (FIG. 5c).

[0566] FIG. 6 shows the spectrum of the Pd (2%)/CeO.sub.2 catalyst (HSA 20 SP) at the binding energies corresponding to Pd 3d and the assignment of the corresponding bonds to the peaks.

[0567] FIG. 7 shows the spectra of the Pd (2%)/CeO.sub.2 catalyst (HSA 20 SP) at the binding energies corresponding to Pd 3d at two different exposure times.

[0568] FIG. 8 shows the spectra of the Pd (2%)Mn (1%)/CeO.sub.2 catalyst (HSA 20 SP) at the binding energies corresponding to Pd 3d (FIG. 8a), Mn 2p.sup.3 (FIG. 8b), Ce 3d (FIG. 8c) and O 1s (FIG. 8d).

EXAMPLES

Example 1Materials and Methods

[0569] The two supports used in CeO.sub.2, under the trade names HSA 85 and HSA 20 SP respectively, come from Solvay.

[0570] HSA 85 has a specific surface area of 273 m.sup.2/g, a surface area after calcination at 800 C. for 2 hours of 55.0 m.sup.2/g, a median pore size D (50) of 6.7 m and a loss on ignition (LOI) of less than 7.9%.

[0571] HSA 20SP has a specific surface area of 159 m.sup.2/g, a surface area after calcination at 900 C. for 5 hours of 45.9 m.sup.2/g, a median pore size D (50) of 12 m and a loss on ignition (LOI) of less than 3%.

[0572] The -Al.sub.2O.sub.3 support was supplied by Sigma Aldrich.

[0573] The -Al.sub.2O.sub.3, ZrO.sub.2 support and the Pd/C catalyst were supplied by Strem Chemicals (15 Rue de l'Atome, 67800 Bischheim).

[0574] Palladium nitrate (Pd(NO.sub.3).sub.2.Math.xH.sub.2O) and other metal salts (dopants) such as Mn(OAc).sub.2, Ca(NO.sub.3).sub.2.Math.3H.sub.2O, Fe(NO.sub.3).sub.3.Math.9H.sub.2O, Mg(NO.sub.3).sub.3.Math.6H.sub.2O were supplied by Fischer. The autoclave is supplied by Parr Instrument Company.

Example 2General Procedure for the Preparation of Heterogeneous Pd/CeO.SUB.2 .Catalysts

[0575] The palladium salt, Pd(NO.sub.3).sub.2.Math.xH.sub.2O (corresponding concentration in Pd content by weight with respect to the total weight of the catalyst) was dissolved in a minimum volume of demineralised water, forming a solution. This solution was added to the appropriate amount of cerium dioxide support (HSA 85 or HSA 20 SP) with a solution mass/support mass ratio from 0.6 to 1, and the resulting paste of CeO.sub.2 was mixed at room temperature until a homogeneous material was obtained. The material was then dried at 80 C. for 16 hours and calcined at 600 C. for 2 hours to obtain the catalyst.

Example 3Preparation of Heterogeneous Pd/CeO.SUB.2 .Catalysts and Surface Analysis

[0576] Table 1 below shows the conditions for preparing Pd/CeO.sub.2 catalysts according to Example 2.

TABLE-US-00001 TABLE 1 Prepared Pd/CeO.sub.2 catalysts CeO.sub.2 Support Catalyst (g) Pd(NO.sub.3).sub.2xHO.sub.2 Pd (2%)/CeO.sub.2 HSA 85 504 mg (HSA 85) (10 g) Pd (5%)/CeO.sub.2 HSA 85 1260 mg (HSA 85) (10 g) Pd (1%)/CeO.sub.2 HSA 20 SP 257 mg (HSA 20SP) (10 g) Pd (2%)/CeO.sub.2 HSA 20 SP 504 mg (HSA 20SP) (10 g) Pd (5%)/CeO.sub.2 HSA 20 SP 1260 mg (HSA 20SP) (10 g) Pd (10%)/CeO.sub.2 HSA 20 SP 2570 mg (HSA 20SP) (10 g)

[0577] Table 2 shows the results of the analysis of the specific surface area of the catalysts prepared by the BET method.

TABLE-US-00002 TABLE 2 Surface area of prepared Pd/CeO.sub.2 catalysts Specific surface Catalysts area (m.sup.2/g) Pd (2%)/CeO.sub.2 (HSA 85) 185.79 m.sup.2/g Pd (2%)/CeO.sub.2 (HSA 20SP) 142.15 m.sup.2/g

Example 4General Procedure for the Preparation of Heterogeneous Pd-M/CeO.SUB.2 .Catalysts

[0578] Pd(NO.sub.3).sub.2.Math.xH.sub.2O and the metal salt (corresponding dopant) were dissolved in a minimum volume of demineralised water, forming a solution. This solution containing the metal precursors was added to the appropriate amount of cerium dioxide support (HSA 85 or HSA 20 SP) and the resulting paste of CeO.sub.2 was mixed at room temperature until a homogeneous material was obtained. The material was then dried at 80 C. for 16 hours and calcined at 600 C. for 2 hours to obtain the catalyst.

Example 5Preparation of Heterogeneous PdX/CeO.SUB.2.-Doped Catalysts.SUB.2 .and Analysis

[0579] Table 3 below shows the preparation conditions for the Pd/CeO.sub.2 catalysts prepared according to example 4.

TABLE-US-00003 TABLE 3 Prepared Pd-X/CeO.sub.2 doped catalysts CeO.sub.2 Salt of Support the dopant Catalyst (g) Pd(NO.sub.3).sub.2xHO.sub.2 (mg) Pd(2%)-Mn(0.5%)/ HSA 20 SP 504 mg Mn(OAc).sub.2 CeO.sub.2 (10 g) (165 mg) (HSA 20 SP) Pd (2%)-Mn(1%)/ HSA 20 SP 504 mg Mn(OAc).sub.2 CeO.sub.2) (10 g) (330 mg) (HSA 20 SP) Pd (2%)-Mn(2%)/ HSA 20 SP 504 mg Mn(OAc).sub.2 CeO.sub.2 (10 g) (660 mg) (HSA 20 SP) Pd (2%)-Mn(5%)/ HSA 20 SP 504 mg Mn(OAc).sub.2 CeO.sub.2 (10 g) (825 mg) (HSA 20 SP) Pd(2%)-Fe(1%)/ HSA 20 SP 504 mg Fe(NO.sub.3).sub.39H O.sub.2 CeO.sub.2 (10 g) (769 mg) (HSA 20 SP) Pd(2%)-Mg(1%)/ HSA 20 SP 504 mg Mg(NO.sub.3).sub.36H O.sub.2 CeO.sub.2 (10 g) (1,310 mg) (HSA 20 SP) Pd (2%)-Ca(1%)/ HSA 20 SP 504 mg Ca(NO.sub.3).sub.23H O.sub.2 CeO.sub.2 (10 g) (699 mg) (HSA 20 SP)

[0580] Table 4 shows the results of the BET surface area analysis of a PdX-doped catalyst.

TABLE-US-00004 TABLE 4 Surface area of the prepared Pd-Mn/CeO.sub.2 catalyst Specific surface Catalysts area (m.sup.2/g) Pd (2%)Mn(1%)/CeO.sub.2 132.10 m.sup.2/g (HSA 20SP)

Example 6-Preparation of Heterogeneous Pd Catalysts on Other Supports

Pd/-Al.sub.2O.sub.3 and Pd/ZrO.sub.2 Catalysts

[0581] The palladium salt, Pd(NO.sub.3).sub.2.Math.xH.sub.2O (corresponding concentration in terms of Pd content by weight relative to the total weight of the catalyst) was dissolved in a minimum volume of demineralised water, forming a solution. The solution was added to the appropriate amount of oxide support (-A Al.sub.2O.sub.3 or ZrO.sub.2); the resulting paste was mixed at room temperature until a homogeneous mixture was obtained. The material was then dried at 80 C. for 16 h. The catalyst was then calcined at 600 C. for 2 hours.

[0582] Table 5 below shows the preparation conditions for the Pd/-Al O.sub.23 and Pd/ZrO.sub.2. catalysts.

TABLE-US-00005 TABLE 5 Prior art catalysts Catalyst Support (g) Pd(NO.sub.3).sub.2xH.sub.2O Pd (2%)/- Al.sub.2O.sub.3 - Al.sub.2O.sub.3 (10 g) 504 mg Pd (5%)/ZrO.sub.2 ZrO.sub.2 (10 g) 504 mg [0583] Pd/C catalysts: The Pd (10%)/C catalyst is supplied by Strem. [0584] PdCl.sub.2/CeO.sub.2: catalyst The PdCl.sub.2 (3%)/CeO.sub.2 catalyst is prepared according to the Gaffney et al. paper (Journal of Catalysis, 1984, 90, 261-269). [0585] PdCe/-Al.sub.2O.sub.3 catalysts: The Pd (1%)Ce (0.8%)/-Al.sub.2O.sub.3 catalyst is prepared according to Appl. Cat. A, 2005, 284 (1-2), 253-257. [0586] Pd/CeO.sub.2 catalysts-Al.sub.2O.sub.3: The Pd/CeO.sub.2 catalyst-Al.sub.2O.sub.3 is prepared according to RSC Adv., 2014, 4, 48901-48904.

Example 7General Heterogeneous Catalysis Procedure for the Oxidative Carbonylation of Methanol to Oxalates

[0587] A heterogeneous palladium-based catalyst (0.7 mmol or 0.24 mmol Pd), tetrabutylammonium iodide TBAI (554 mg, 1.5 mmol) as promoter, tri-ethylamine Et.sub.3N (0.14 mL, 1.0 mmol), acetonitrile (50 mL) and methanol (25 mL) were introduced into a 450 mL Parr autoclave equipped with a magnetic stirrer. The reactor was sealed and the reaction mixture purged three times with nitrogen (5 bars) and twice with oxygen (5 bars).

[0588] The autoclave was then pressurised with 15 bars of oxygen and a further 65 bars of carbon monoxide (total pressure of 80 bars). The reaction medium was then stirred at 90 C. for 16 h or 60 h.

[0589] Once the reaction was complete, the autoclave was brought to room temperature before being depressurised and purged three times with nitrogen (5 bars).

[0590] The final mixture obtained was then filtered and transferred to a 250 mL flask.

[0591] The reaction solvent and excess alcohol were separated by evaporation on a rotary evaporator. The dimethyloxalate was recovered after purification by recrystallisation in di-ethyl ether and the isolated yields were calculated.

[0592] For reactions with alcohols, the results are described in terms of NCC rather than percentage yield due to the excess use of the substrate, the alcohol (or also the absence of solvent, in this case substrate=solvent).

[0593] The NCC is calculated as follows:

NCC=number of moles of product formed/number of moles of Pd

Example 8: Reaction with 0.7 Mmol of Catalyst

[0594] Table 6 below shows the conditions for preparing dimethyloxalate with Pd/CeO.sub.2 catalysts and Pd on other supports (for comparison) and the yield results obtained in terms of isolated mass and NCC.

TABLE-US-00006 TABLE 6 Conditions for the preparation of dimethyloxalate with heterogeneous palladium catalysts at a content of 0.7 mmol and the results obtained. Base Promoteur Solvent, O.sub.2/CO T Time, Reaction Cat (mmol) (mmol) (ml) (bar) ( C.) (h) Substrate Results M1 Pd(2%)- Et.sub.3N TBAI MeCN; 15/65 90 60 25 mL 7.41 g CeO.sub.2 (1 (1.5 mmol) 50 mL MeOH NCC: (HSA 20 mmol) 90 SP) (0.7 mmol) M2 Pd(5%)- Et.sub.3N TBAI MeCN; 15/65 90 60 25 mL 6.6 g CeO.sub.2 (1 (1.5 mmol) 50 mL MeOH NCC: (HSA 85) mmol) 80 (0.7 mmol) M3 Pd(5%)- Et.sub.3N TBAI MeCN; 15/65 90 60 25 mL 6.35 g CeO.sub.2 (1 (1.5 mmol) 50 mL MeOH NCC: (HSA 20 mmol) 77 SP) (0.7 mmol) M4 Pd(5%)-- Et.sub.3N TBAI MeCN; 15/65 90 16 25 mL 3 g Al.sub.2O.sub.3 (1 (1.5 mmol) 50 mL MeOH NCC: (0.7 mmol) mmol) 36 M5 Pd(5%)-- Et.sub.3N TBAI MeCN; 15/65 90 60 25 mL 3.5 g Al.sub.2O.sub.3 (1 (1.5 mmol) 50 mL MeOH NCC: (0.7 mmol) mmol) 42 M6 Pd(10%)/C Et.sub.3N TBAI MeCN; 15/65 90 16 25 mL 5.7 g (0.7 mmol) (1 (1.5 mmol) 50 mL MeOH NCC: mmol) 69

[0595] Carried out under the same conditions, the results of M1, M2 and M3 with the catalysts of the invention show a higher yield by mass of isolated product and a higher NCC than those of the tests with the catalysts on different supports of the prior art (M4, M5 and M6). The yield of the catalysts according to the invention is greater than 6 g. In particular, M1 shows that a preparation with a catalyst containing 2% Pd on the HSA 20 SP support gives a higher yield with catalysts containing 5% Pd.

[0596] Under the same operating conditions, the results of the invention's Pd/CeO.sub.2 catalysts are superior to those of the prior art.

[0597] Furthermore, in this range of 100 to 250 m.sup.2/g, the catalysts were unexpectedly found to have substantially equivalent activities, as demonstrated by the tests in Table 6. A comparison of tests M2 and M3 shows that the Pd (5%)/HSA 85 catalyst (186 m.sup.2/g) and the Pd (5%)/HSA 20 SP catalyst (142 m.sup.2/g), i.e. with a difference of approximately 44 m.sup.2/g, exhibit almost identical yields with NCCs of 80 and 77 respectively.

Example 9:0.24 Mmol Catalyst

[0598] Table 7 below shows the conditions under which dimethyloxalate was prepared using Pd/CeO.sub.2 catalysts at a content of 0.24 mmol and Pd catalysts on other supports (for comparison) and the yield results obtained in terms of product mass and NCC.

TABLE-US-00007 TABLE 7 Conditions for the preparation of dimethyloxalate with heterogeneous palladium catalysts at a content of 0.24 mmol and results obtained. Base Promoteur Solvent, O.sub.2/CO T Time, Reaction Cat (mmol) (mmol) (ml) (bar) ( C.) (h) Substrate Results M7 Pd(1%)- Et.sub.3N TBAI MeCN; 15/65 90 16 25 mL 3.32 g CeO.sub.2 (1 (1.5 mmol) 50 mL MeOH NCC: (HSA 20 mmol) 117 SP) (0.24 mmol) M8 Pd(2%)- Et.sub.3N TBAI MeCN; 15/65 90 16 25 mL 4.77 g CeO.sub.2 (1 (1.5 mmol) 50 mL MeOH NCC: (HSA 20 mmol) 168 SP) (0.24 mmol) M9 Pd(5%)- Et.sub.3N TBAI MeCN; 15/65 90 16 25 mL 3 g CeO.sub.2 (1 (1.5 mmol) 50 mL MeOH NCC: (HSA 20 mmol) 106 SP) (0.24 mmol) M10 Pd(10%)- Et.sub.3N TBAI MeCN; 15/65 90 16 25 mL 3.7 g CeO.sub.2 (1 (1.5 mmol) 50 mL MeOH NCC: (HSA 20 mmol) 130 SP) (0.24 mmol) M11 Pd(2%)- Et.sub.3N TBAI MeCN; 15/65 90 16 25 mL 1.77 g -Al.sub.2O.sub.3 (1 (1.5 mmol) 50 mL MeOH NCC: (0.24 mmol) 63 mmol) M12 Pd(2%)- Et.sub.3N TBAI MeCN; 15/65 90 16 25 mL 1.81 g -Al.sub.2O.sub.3 (1 (1.5 mmol) 50 mL MeOH NCC: (0.24 mmol) 64 mmol) M13 Pd(2%)- Et.sub.3N TBAI MeCN; 15/65 90 16 25 mL 3.2 g r.sub.(0.24 (1 (1.5 mmol) 50 mL MeOH NCC: mmol) mmol) 113 M14 Pd(10%/C) Et.sub.3N TBAI MeCN; 15/65 90 16 25 mL 4.4 g (0.24 (1 (1.5 mmol) 50 mL MeOH NCC: mmol) mmol) 155

[0599] At a similar Pd content of 2%, the results of M8 with a catalyst according to the invention are superior to the results of Pd catalysts on different oxide supports (M11, M12 and M13).

[0600] The results of M7, M8, M9 and M10 on Pd/CeO.sub.2 catalysts suggest that optimisation by Pd content is possible.

[0601] Tests M8 and M14 indicate that the Pd/CeO.sub.2 catalyst can perform better than a commercial carbon-supported Pd catalyst.

Example 10: Reaction with a Prior Art Catalyst

[0602] Table 8 below shows the preparation conditions with prior art Pd catalysts (for comparison) according to example 6 and the yields obtained.

TABLE-US-00008 TABLE 8 Conditions for the preparation of dimethyloxalate and results obtained with the heterogeneous palladium catalysts of the prior art on different supports. Base Promoteur Solvent, O.sub.2/CO T Time, Reaction Cat (mmol) (mmol) (ml) (bar) ( C.) (h) Substrate Results A1 Pd(3%)Cl.sub.2/ Et.sub.3N TBAI MeCN; 15/65 90 16 25 mL 0.750 g CeO.sub.2 (1 (1.5 mmol) 50 mL MeOH NCC: (0.24 mmol) 26 mmol) A2 Pd(1%)- Et.sub.3N TBAI MeCN; 15/65 90 60 25 mL 3.12 g Ce (0.8%)/ (1 (1.5 mmol) 50 mL MeOH NCC: -Al.sub.2O.sub.3 mmol) 110 (0.24 mmol) A3 Pd/CeO.sub.2- Et.sub.3N TBAI MeCN; 15/65 90 60 25 mL 1.00 g -Al.sub.2O.sub.3 (1 (1.5 mmol) 50 mL MeOH NCC: (0.24 mmol) 35 mmol)

[0603] Comparison of the tests with a catalyst according to the invention (M8) and test A1, i.e. a catalyst prepared according to Gaffney et al. reveals an NCC yield of 168 for M8 and a lower NCC yield of 26 for A1, which confirms the superior efficiency of the catalysts according to the invention.

Example 11: Reaction with a Pd-M/CeO.SUB.2 .Bimetallic Catalyst

[0604] Table 9 below shows the preparation conditions and results with PdX-doped catalysts.

TABLE-US-00009 TABLE 9 Preparation conditions for dimethyloxalates and results obtained with Pd-X/CeO doped heterogeneous catalysts.sub.2. Base Promoteur Solvent, O.sub.2/CO T Time, Reaction Cat (mmol) (mmol) (ml) (bar) (C) (h) Substrate Results D1 Pd(2%)- Et.sub.3N TBAI MeCN; 15/65 90 16 25 mL 4.97 g Mn(1%)/ (1 (1.5 mmol) 50 mL MeOH NCC: CeO.sub.2 mmol) 176 (HSA 20 SP) (0.24 mmol) D2 Pd(2%)- Et.sub.3N TBAI MeCN; 15/65 90 16 25 mL 2.52 g Ca(1%)- (1 (1.5 mmol) 50 mL MeOH NCC: CeO.sub.2 mmol) 89 (HSA 20 SP) (0.24 mmol)

[0605] Tests D1 and D2 show the effect of doping the Pd/CeOz catalyst.

[0606] In particular, manganese doping improves the properties of the catalyst.

Example 12: Reaction with PdMn/CeO.SUB.2 .Catalyst

[0607] Table 10 below shows the conditions under which dimethyloxalate was prepared using PdMn/CeO.sub.2 manganese-doped catalysts and the yield results obtained in terms of product mass and NCC.

TABLE-US-00010 TABLE 10 Conditions for preparing dimethyloxalate with manganese-doped Pd-X/CeO.sub.2 heterogeneous catalysts and results obtained. Base Promoteur Solvent, O.sub.2/CO T Time, Reaction Cat (mmol) (mmol) (ml) (bar) ( C.) (h) Substrate Results M8 Pd(2%)- Et.sub.3N TBAI MeCN; 15/65 90 16 25 mL 4.77 g CeO.sub.2 (1 (1.5 mmol) 50 mL MeOH NCC: (HSA 20 mmol) 168 SP) (0.24 mmol) D3 Pd(2%)- Et.sub.3N TBAI MeCN; 15/65 90 16 25 mL 3.43 g Mn(0.5%)- (1 (1.5 mmol) 50 mL MeOH NCC: CeO.sub.2 mmol) 121 (HSA 20 SP) (0.24 mmol) D1 Pd(2%)- Et.sub.3N TBAI MeCN; 15/65 90 16 25 mL 4.97 g Mn(1%)- (1 (1.5 mmol) 50 mL MeOH NCC: CeO.sub.2 mmol) 176 (HSA 20 SP) (0.24 mmol) D4 Pd(2%)- Et.sub.3N TBAI MeCN; 15/65 90 16 25 mL 3.53 g Mn(2%)- (1 (1.5 mmol) 50 mL MeOH NCC: CeO.sub.2 mmol) 125 (HSA 20 SP) (0.24 mmol) D5 Pd(2%)- Et.sub.3N TBAI MeCN; 15/65 90 16 25 mL 2.68 g Mn(5%)- (1 (1.5 mmol) 50 mL MeOH NCC: CeO.sub.2 mmol) 95 (HSA 20 SP) (0.24 mmol)

Example 13General Heterogeneous Catalysis Procedure for the Oxidative Carbonylation of Ethanol to Oxalates

[0608] In a 450 mL Parr autoclave, equipped with a magnetic stirrer, a heterogeneous palladium catalyst (0.7 mmol or 0.24 mmol Pd), tetrabutylammonium iodide TBAI (1.5 to 3.6 mmol), tri-ethylamine Et.sub.3N (1.0 to 4.75 mmol), optionally acetonitrile MeCN (25 to 75 mL) as solvent and ethanol (25 to 75 mL) have been introduced. The reactor was sealed and the reaction mixture was purged three times with nitrogen (5 bars) and twice with oxygen (5 bars).

[0609] The autoclave was then pressurised with 15 bars of oxygen and a further 65 bars of carbon monoxide (total pressure of 80 bars). The reaction medium was then stirred at 90 C. for 16 h. Once the reaction was complete, the autoclave was brought to room temperature before being depressurised and purged three times with nitrogen (5 bars).

[0610] The final mixture obtained was then filtered and transferred to a 250 mL flask.

[0611] The reaction solvent and excess alcohol were separated by evaporation on a rotary evaporator.

[0612] The diethyloxalate was recovered after purification by vacuum distillation at 120 C./50-20 mbars and the isolated yields were calculated.

Example 14: Heterogeneous Catalysis of the Oxidative Carbonylation of Ethanol to Oxalates

[0613] Table 11 below shows the preparation conditions using the heterogeneous PdX/CeO.sub.2 catalysts for diethyloxalate and the yield results obtained in terms of mass of product isolated and NCC.

TABLE-US-00011 TABLE 11 Conditions for the preparation of diethyloxalate with heterogeneous Pd-X/CeO.sub.2 catalysts and results obtained. Base Promoter Solvent, O.sub.2/CO T, Time, Reaction Cat (mmol) (mmol) (ml) (bar) ( C.) (h) Substrate Results E Pd(5%)/ Et.sub.3N TBAI x 15/65 90 16 75 mL 5.6 g CeO.sub.2 (1.5) (2) EtOH NCC = (HSA 85) 55 (0.7 mmol) E2 Pd(5%)/CeO.sub.2 Et.sub.3N TBAI MeCN; 15/65 90 16 50 mL 7.0 g (HAS 85) (1.5) (2) 100 mL EtOH NCC = (0.7 68 mmol) E3 Pd(2%)/CeO.sub.2 Et.sub.3N TBAI MeCN; 15/65 90 16 25 mL 5.3 g (HSA 20 (1) (1.5) 50 mL EtOH NCC = SP) 151 (0.24 mmol) E4 Pd(2%)- Et.sub.3N TBAI MeCN; 15/65 90 16 25 mL 6.0 g Mn(1)- (1) (1.5) 50 mL EtOH NCC = CeO.sub.2 171 (HSA 20 SP) (0.24 mmol)

[0614] Reaction E1 shows that it is possible to operate without a solvent.

Example 15Heterogeneous Catalysis Procedure for the Oxidative Carbonylation of Isopropanol to Oxalates

[0615] A heterogeneous palladium catalyst (0.7 mmol Pd), tetrabutylammonium iodide (554 mg, 1.0 mmol), triethylamine (1.5 mmol), acetonitrile (50 mL) and isopropanol (25 mL) were added to a 450 mL Parr autoclave equipped with a magnetic stirrer. The reactor was sealed and the reaction mixture purged three times with nitrogen (5 bars) and twice with oxygen (5 bars). The autoclave was then pressurised with 15 bars of oxygen and a further 65 bars of carbon monoxide (total pressure of 80 bars). The reaction medium was then stirred at 90 C. for 16 h. Once the reaction was complete, the autoclave was brought to room temperature before being depressurised and purged three times with nitrogen (5 bars).

[0616] The final mixture obtained was then filtered and transferred to a 250 mL flask.

[0617] The reaction solvent and excess alcohol were separated by evaporation on a rotary evaporator. The oxalate was recovered after purification (vacuum distillation or recrystallisation) and the isolated yields were calculated.

[0618] Table 12 below shows the preparation conditions.

TABLE-US-00012 TABLE 12 Conditions for the preparation of diisopropyloxalate with a heterogeneous Pd-X/CeO.sub.2 catalyst Base Promoter Solvent O.sub.2/CO T, Time, Reaction Catalyst (mmol) (mmol) (ml) (bar) ( C.) (h) Substrate P1 Pd(5%)/CeO.sub.2 Et.sub.3N TBAI MeCN; 15/65 90 16 25 mL (HSA (1) (1.5) 50 mL iPrOH 85) (0.7 mmol)

Example 16: General Heterogeneous Catalysis Procedure for the Oxidative Carbonylation of Piperidine to Oxamides

[0619] Heterogeneous palladium catalyst (0.7 mmol Pd), tetrabutylammonium iodide TBAI (554 mg, 1.5 mmol), optionally tri-ethylamine Et.sub.3N (0.14 mL, 1.0 mmol) as added base, MeCN acetonitrile (50 mL) and (1.98 mL, 20 mmol) piperidine were introduced into a 450 mL Parr autoclave, equipped with a magnetic stirrer. The reactor was sealed and the reaction mixture purged three times with nitrogen (5 bars) and twice with oxygen (5 bars). The autoclave was then pressurised with 10 bars of oxygen and a further 45 bars of carbon monoxide (total pressure 55 bars). The reaction medium was then kept stirred at 25 C. for 16 h. Once the reaction was complete, the autoclave was depressurised and purged three times with nitrogen (5 bars). The final mixture obtained was then filtered and transferred to a 250 mL flask. The solvent was evaporated and the residue obtained was solubilised in toluene and then filtered over Celite. The toluene solution was evaporated and a yellow solid was obtained.

Example 17: Preparation of a Piperidine Oxamide Compound

[0620] Table 13 below shows the conditions for preparing oxamide from piperidine using Pd/CeO.sub.2 catalysts and the percentage yield results.

TABLE-US-00013 TABLE 13 Conditions for the preparation of oxamide with piperidine and results obtained with the heterogeneous Pd-X/CeO.sub.2 catalysts. Base Promoter Solvent, O.sub.2/CO T Time Reaction substrate Cat (mmol) (mmol) (ml) (bar) ( C.) (h) Yield Pi1 20 mmol Pd(5%)- Et.sub.3N TBAI MeCN; 10/45 25 16 95% CeO.sub.2 (1 (1.5 mmol) 50 mL (HSA mmol) 85) (0.7 mmol) Pi2 20 mmol Pd(2%)- Et.sub.3N TBAI MeCN; 10/45 25 16 94% CeO.sub.2 (1 (1.5 mmol) 50 mL (HSA mmol) 20 SP) (0.7 mmol) Pi3 20 mmol Pd(2%)- X TBAI MeCN; 10/45 25 16 74% CeO.sub.2 (1.5 mmol) 50 mL (HSA 20 SP) (0.7 mmol))

[0621] Reactions Pi1, Pi2 and Pi3 were carried out at room temperature, so it was not necessary to heat the reaction medium.

[0622] The Pi1 and Pi2 reactions showed yields of over 90%, in the presence of the base, triethylamine. Reaction Pi3 shows that it is possible to operate without adding a base, with the amine acting as the base in the reaction medium.

[0623] Example 18 Heterogeneous Palladium-Manganese/CeO.sub.2 catalysis of the oxidative carbonylation of ethanol to oxalates

[0624] The Pd (2%)Mn (1%)/CeO.sub.2 catalyst (HSA 20SP) was prepared according to example 5. The tests were carried out in 2 autoclaves of different volumes: [0625] or in a 450 mL Parr autoclave [0626] or in a 1 L Parr autoclave when 100 mL of the substrate is introduced.

[0627] A 450 mL Parr autoclave equipped with a magnetic stirrer was charged with a heterogeneous palladium-based catalyst (0.24 mmol Pd), tetrabutylammonium iodide (554 mg, 1.5 mmol), tri-ethylamine (0.28 mL, 2.0 mmol), acetonitrile (50 mL) and ethanol (50 mL). The reactor was sealed and the reaction mixture was purged three times with nitrogen (5 bars) and twice with oxygen (5 bars). The autoclave was then pressurised with 15 bars of oxygen and a further 65 bars of carbon monoxide (total pressure 80 bars). The reaction mixture was then stirred at 90 C. for 16 h. Once the reaction was complete, the autoclave was returned to room temperature before being depressurised and purged three times with nitrogen (5 bars). The reaction mixture was then filtered and the solution transferred to a 250 mL flask. The reaction solvent and excess alcohol were separated by evaporation on a rotary evaporator. The oxalate was recovered after purification (vacuum distillation at 120 C./50-20 mbars for the diethyloxalate) and the isolated yields were calculated.

[0628] A 1 L Parr autoclave equipped with a magnetic stirrer was charged with a heterogeneous palladium-based catalyst (0.48 mmol Pd), tetrabutylammonium iodide (1.11 g, 3 mmol), tri-ethylamine (0.56 mL, 4.0 mmol), acetonitrile (100 mL) and ethanol (100 mL). The reactor was sealed and the reaction mixture was purged three times with nitrogen (5 bars) and twice with oxygen (5 bars). The autoclave was then pressurised with 15 bars of oxygen and a further 65 bars of carbon monoxide (total pressure 80 bars). The reaction mixture was then stirred at 90 C. for 16 h. Once the reaction was complete, the autoclave was returned to room temperature before being depressurised and purged three times with nitrogen (5 bars). The reaction mixture was then filtered and the solution transferred to a 500 mL flask. The reaction solvent and excess alcohol were separated by evaporation on a rotary evaporator. The oxalate was recovered after purification (vacuum distillation at 120 C./50-20 mbars for the diethyloxalate) and the isolated yields were calculated.

[0629] Table 14 below shows the conditions under which diethyloxalate was prepared using Pd (2%)Mn(1%)/CeO.sub.2 catalysts and the results obtained in terms of product mass and NCC.

TABLE-US-00014 TABLE 14 Conditions for the preparation of diethyloxalate with Pd(2%)-Mn(1%)/CeO catalysts.sub.2 and the results obtained in terms of product mass and NCC. Base Promoter Solvant O2/CO T Time Reaction Cat (mmol) (mmol) (ml) (bar) C. (h) Substrate Results 1 Pd(2%)- Et3N TBAI MeCN; 15/65 90 16 25 mL 6 g Mn(1%)-CeO2 (1) (1.5) 50 mL EtOH NCC = (HSA 20 SP) 171 (0.24 mmol) 2 Pd(2%)- Et3N TBAI MeCN; 15/65 90 16 50 mL 8.5 g Mn(1%)-CeO2 (1) (1.5) 50 mL EtOH NCC = (HSA 20 SP) 242 (0.24 mmol) 3 Pd(2%)- Et3N TBAI MeCN; 15/65 90 16 75 mL 6.2 g Mn(1%)-CeO2 (1) (1.5) 25 mL EtOH NCC = (HSA 20 SP) 177 (0.24 mmol) 4 Pd(2%)- Et3N TBAI MeCN; 15/65 90 16 100 mL 18.7 g Mn(1%)-CeO2 (2) (3) 100 mL EtOH NCC = (HSA 20 SP) 267 (0.48 mmol) (reactor 1 L) 5 Pd(2%)- Et3N NaI MeCN 15/65 90 16 50 mL 1.88 g Mn(1%)-CeO2 (1) (1.5) 50 mL EtOH NCC = (HSA 20 SP) 54 (0.24 mmol) 6 Pd(2%)- Et3N TBAI MeCN 15/65 90 16 50 mL 9.58 g Mn(1%)-CeO2 (2) (1.5) 50 mL EtOH NCC = (HSA 20 SP) 273 (0.24 mmol) 7 Pd(2%)- Et3N TBAI MeCN 15/65 90 16 50 mL 11 g Mn(1%)-CeO2 (2) (1.5) 50 mL EtOH NCC = (HSA 20 SP) 157 (0.48 mmol) 8 Pd(2%)- Et3N TBAI MeCN 15/65 90 16 50 mL 0.48 g Mn(1%)-CeO2 (0) (1.5) 50 mL EtOH NCC = (HSA 20 SP) 14 (0.24 mmol) 9 Pd(2%)- Et3N TBAI MeCN 10/45 90 16 50 mL 5.94 g Mn(1%)-CeO2 (1) (1.5) 50 mL EtOH NCC = (HSA 20 SP) 170 (0.24 mmol) 10 Pd(2%)- Et3N TBAI MeCN 15/65 90 16 50 mL 7.5 g Mn(1%)-CeO2 (4) (1.5) 50 mL EtOH NCC = (HSA 20 SP) 214 (0.24 mmol) 11 Pd(2%)- Et3N TBAI MeCN 15/65 90 16 100 mL 23 g Mn(1%)-CeO2 (4) (3) 100 mL EtOH NCC = (HSA 20 SP) 328 (0.24 mmol) (reactor 1 L)

Example 19: Structural Characterisation of Catalysts

[0630] X-ray powder diffraction analysis was carried out on the HSA 20SP ceria support, the Pd (2%)/CeO.sub.2 catalyst (HSA 20 SP) prepared according to example 3 and the Pd (2%)Mn(1%)/CeO.sub.2 catalyst (HSA 20 SP) prepared according to example 5 were analysed by X-ray diffraction using a Rigaku MINIFLEX II diffractometer, the X-rays emitted by which are obtained by a copper tube and source (wavelength K 1.54 ).

[0631] The three diffractograms in FIG. 1 show peaks corresponding to the (111), (200), (220), (311), (222), (400) and (311) planes, attributable to a fluorine structure of cerium oxide (JCPDS 34-0394). There is a distinct broadening of the diffraction peaks.

Crystallite Size

[0632] The size of the crystallites was estimated qualitatively in order to compare with the various catalysts in the prior art, in particular the catalysts and their support described in Kai Li et al. (Front. Chem. Sci. Eng. 2020, 14 (6); 929-936).

[0633] The size of the crystallites was evaluated using the following Scherrer formula:

[00003]$\begin{array}{cc}t=\frac{k.}{H.\cos }& t=\mathrm{crystallite}\mathrm{size}\\ & k=\mathrm{correction}\mathrm{factor}=0.89\\ & =\mathrm{wavelength}\mathrm{of}\mathrm{the}\mathrm{source}\\ & H=\mathrm{width}\mathrm{at}\mathrm{half}-\mathrm{height}\mathrm{of}\mathrm{the}\mathrm{peak}\left(\mathrm{in}\mathrm{radians}\right)\\ & =\mathrm{diffraction}\mathrm{angle}\end{array}$

[0634] It should be noted that the correction due to defects in the instrumental optics has not been taken into account in the estimated calculations, as its contribution to peak broadening is considered negligible to a first approximation.

[0635] The width at mid-height was estimated using Image J

[0636] The crystallite size calculations were carried out using the peak of the diffractograms located at approximately 28 degrees and are reported in the following table:

TABLE-US-00015 TABLE 15 Crystallite sizes Crystallite Width at sizes half-height H Reference Support or Catalyst (nm) (degrees) Kai Li et al. CeO.sub.2 support - 58.7 0.138 from Alfa Aesar Example 1 CeO.sub.2 support - 7.9 1.02 HSA 20SP - from Solvay Kai Li et al. Pd/CeO.sub.2 42.0 0.193 (calcination treatment at 600 C.) Example 3 Pd(2%)/CeO.sub.2 7.7 1.048 (HSA 20 SP) Example 5 Pd(2%)-Mn(1%)/CeO.sub.2 7.2 1.128 (HSA 20 SP)

[0637] The support used in Kai Li et al. is a commercial cerium oxide powder from Alfa Aesar, with a pore volume of 0.18 mL/g and an average pore size of 12.2 nm with a specific surface area of 5.8 m.sup.2/g (BET).

[0638] The low value of the sizes, in particular less than 10 nanometres, is an indicator of a low crystallinity structure. The smaller the crystallites, the wider the diffraction peaks. This effect becomes visible for crystallites less than 1 m in diameter.

[0639] The results indicate that the cerium oxide support and the catalysts described by Kai Li et al. have crystallite sizes of 42 nm to 59 nm respectively and the HSA 20SP support and the catalysts according to the invention have crystallite sizes of less than 10 nanometres, i.e. around 8 nm.

[0640] In addition to the specific surface area, these results show that the microstructure of the supports and catalysts differs from those described in Kai Li et al. with the catalysts of the invention exhibiting lower crystallinity.

Example 20: Morphological Characterisation of Catalysts

[0641] Morphological analysis was carried out by scanning electron microscopy (SEM) using a ZEISS Sigma HD SEM-FEG apparatus on 3 catalysts of the invention: [0642] the Pd (2%)/CeO.sub.2 catalyst (HSA 85 SP), [0643] and the Pd(2%)/CeO.sub.2 catalyst (HSA 20 SP) prepared according to example 3 [0644] and the Pd(2%)Mn (1%)/CeO.sub.2 catalyst (HSA 20 SP) prepared according to example 5.

[0645] The SEM images shown in FIG. 2 of the Pd (2%)/CeO.sub.2 catalyst (HSA 85 SP) reveal a population made up of particles ranging in size from approximately 1 to around 10 micrometres, of any slightly facetted shape, with a specific surface area of 186 m.sup.2/g (BET, see table 2 of example 3).

[0646] The SEM images of FIG. 3 of the Pd (2%)/CeO.sub.2 catalyst (HSA 20 SP) and FIG. 4 of the Pd (2%)Mn(1%)/CeO.sub.2 catalyst (HSA 20 SP) are similar because they were prepared using the same HSA 20SP support and differ only in the presence of 1% by weight of manganese. They reveal a homogeneous population made up of particles around ten micrometres in size, in the form of a compacted agglomerate of round particles (like a truffle), with a specific surface area of 142 m.sup.2/g (BET, see table 2 of example 3).

[0647] SEM images reveal that the morphology of the prepared catalysts differs from the well-crystallized catalysts described in Chao Hu et al. (Catalysis Letter 2002, 152, 503-512) who disclose for Pd/CeO catalysts.sub.2: [0648] a population of cubes around fifty nanometres in size (with a specific surface area of 7.82 m.sup.2/g), [0649] an octahedron population of 20 to 80 nm (with a specific surface area of 7.82 m.sup.2/g), [0650] a population of rods approximately 9 nm wide and 40 to 140 nm long (with a specific surface area of 66 m.sup.2/g)

Example 21: Analysis of the Surface of Catalysts

[0651] The surface of the Pd (2%)/CeO.sub.2 (HSA 20 SP) catalyst prepared according to example 3 and of the Pd (2%)Mn(1%)/CeO.sub.2 (HSA 20 SP) catalyst prepared according to example 5 was analysed by XPS. The results are reported in Tables 16 to 18 and FIGS. 5 to 8.

TABLE-US-00016 TABLE 16 Binding energy of the Pd(2%)/CeO.sub.2 catalyst (HSA 20 SP) Peaks Binding energy (eV) Pd 3d 337.71 This 3d 882.56 O 1s 529.55

TABLE-US-00017 TABLE 17 Binding energy of the Pd 3d peaks of the Pd(2%)/CeO.sub.2 catalyst (HSA 20 SP) Peaks Binding energy (eV) Pd 3d5 PdO 336.05 Pd 3d3 PdO 341.36 Pd 3d5 Pd.sub.xCe.sub.1xO.sub.2 337.82 Pd 3d3 Pd.sub.xCe.sub.1xO.sub.2 343.15

TABLE-US-00018 TABLE 18 Binding energy of the Pd(2%)-Mn(1%)/CeO.sub.2 catalyst (HSA 20 SP) Peaks Binding energy (eV) Pd 3d 338.05 Mn 2p3 641.42 This 3d 882.76 O 1s 529.71

TABLE-US-00019 TABLE 19 Binding energy of Pd 3d peaks of Pd(2%)-Mn(1%)/CeO.sub.2 (HSA 20 SP) Peaks Binding energy (eV) Pd 3d5 PdO 336.11 Pd 3d3 PdO 341.35 Pd 3d5 Pd.sub.xCe.sub.1xO.sub.2 337.88 Pd 3d3 Pd.sub.xCe.sub.1xO.sub.2 343.17

[0652] As shown in Table 17 and FIG. 6, the Pd 3d spectrum can be decomposed into 2 contributions, the one at low binding energy (336.1 eV) can be attributed to PdO bonds, the other at energies around 337.8 eV can be attributed to the Pd.sub.xCe.sub.1-xO.sub.2 species.

[0653] The main difference compared with the article D1 Catalysis Letters, 152 (503-512) 2022 is the presence of Pd(II) of oxidation state 2 in the form of palladium oxide PdO instead of Pd(0) of oxidation state (0).

[0654] These results show that the surface of the catalysts includes both palladium oxide PdO and Pd.sub.xCe.sub.1-xO.sub.2 species but does not include palladium metal Pd(0).

[0655] The spectra in FIG. 7 show a variation in the areas of the peak contributions at two different exposure times (time 1 and time 2) and indicate a palladium reduction phenomenon under the X-ray beam, as the ratio of the PdO and Pd.sub.xCe.sub.1-xO.sub.2 components varies with time.