Indi an Journal of Chemi stry Vol. 45A, July 2006. pp. 1646- 1650

Hydrogenation of cinnamaldehyde over Pt/Zr02 catalyst modified by Cr, Mn ,

Fe, Co, N i and Sn

X iaoxiang Ilan"·h, Renxian 7.hou"·* & Xiaoilling Zheng"

"Il lsti tute of Ca tal ysis. Zhcjia llg Uilive rs ity. Ii allgzhou. 3 10028. P. R. Chilla

"College (,f Fo d Sciellce. Biotechnology & Ell viro llll1elltal J..: llgineerillg. Zhejiallg Cio llgshallg Uili versit y.

Ii allgzhou. 3 10035. P. R. China

Ell1ail: hall -xx74 @ 1()3.colll

i<(' ('C /l'{'(/ 3() Ol'Cl'lIiI}(: r 2005; f(Tisct/ / / Mill' 20()6

1.lyd mge n;lli oll of C ill ll ~ullalcJehydc ICMA ) has beell studied (l ver Pt /ZrO, ;lI1d l' tM/ZrO, cala lys ls (M= Cr. Mil. Fe. Cu. Ni. SIl ) ill t; thanol ;11 .1.43 K alld 2.0 Ml'a . The calal ytic properti es art: , how n to increase upon illtroduct ion o r Il1c ta ls to Pt /Zr0 2 c:llalysl. Ca t;lI ytlc act ivit ies of the c ltal ySl s arc enh ;1I1ccd except I'tC r/ZrO, ca t;lIysl. PtMIl /ZrO, . P1Co/ZrO, and I't FclZrO, cata lys ts show good yie ld or c illlla1l1yl alcohol (CMO). and I't Ni/ZrO, PtSIl/ZrO, cata lys ts , how so()d yield of hyd roc illllall1a lcleh yde ( II CM A) . In the prese nce (l r NaO!! and H20 . rat e "f the hydrogenation 01' CMA increases signiricantl y and side reaction is re lilarkab ly inhibited. I't Co/ZrO! l::l t;i1 ys t shows be:, t ca tal yti c ac ti vit y (TOF 7.4X!0-! >"1) ;llld yicId of CMO (X4.1 11101%). Pt Ni/ZI'O! C;lt ;i1 ys t shows best yie ld or !ICMA (62 .X ll1ol %). More acti ve siles for thc hydrogenation or c=o group on I'tCo/ZrO! cat;i1 yst surrace arc the main reasoll of good se lectiv ity of CMO.

IPC Code: Jill. C l.s BO JJ23/42: J30 J.J27/ J35

The sclec ti ve hydrogenation of C1 , ~ -un sa tura tcd

aldehyde to its unsa turated alcohol , such as cinnamaldehyde to cinnamyl alcohol, is of importance for the synthesis of fine chemica ls used in thc production of pharmaceutical s, flavours and perfumes ' . The traditional mcthods of producing ci nnamy l alcohol, reductants such as aluminium i sopropox ide~ and aluminium bcnzyloxide·1 are used to rcduce cinnamaldehyde. Compared with the trad itional mcthod, the cataly tic selective hydrogenation method is superi or in sav ing resources, red ucing waste disposal and protecting environment. On the sclective hydrogcnation o f C1 , ~-unsaturatcd

aldehyde, cata lys t sys tems investi gated mostly are supported nob le metal catalysts"·5 . Oi fferent nob le metals have different effects on activity and selecti vity. However, the hydrogenation of the C=C bond is thermodynamically more favorable than C=O hydrogenati on and low yields of the desired product

are obtained with the conventional hydrogenation catalysts!>. Many references are reported to develop catalytic systems wi th improved selectivity to C=O hyd rogenation. To improve selecti ve hydrogenation of C=O group, the catalyst preparati ons arc modified (metal particle size7 and support effec ts:; ")) or specific additives (promoters or bimctallic phases")"' ) are uscd in the reaction system. These methods of incrcasing the unsa turated alcohol selec ti vity' re found not to be gcneral. in severa l cascs thei I' effccts hei ng dependent on the reacti on cond iti ons, the structure of thl2 catal ys t and thc subst rate'o.

Catal yt ic hyd rogenation rcacti om: arc influenced by many factors , whi ch include the presence of catal y tic activators or poisons, I.empcrature, pr'cssure, :-;o lvent agitation and othcr cond iti ons spc,:ific to thc part icular process . One of thc more im portant considerations is th c ca tal yst support. Su itab le carri ers such as carbon. clay, alumina. sili ca. zirconia. titania support ed platinum catalys ts have been reported for the hyd rogenati on of fl, f:>-unsaturated aldchyde. Transition metal complexcs have been studi ed widely as homogencous catalysts for the hydrogenation of organic compounds. They have also been used as co­ca tal yst in a large vari cty of chemical rcactions. Polymer-anchored platinum '2-15 and palladium l6

homogeneous ca tal ys ts mod ificd by transition mctal cat ions and its metal complexes show better catalyt ic

properti es on the hydrogenation o f o:,fJ-unsturated aldehydes and chloronitrobenzene_ From the point of v iew of green chemi stry, the deve lopment of industrial processes for direct producti on of organic intermediates using hcterogeneous catalys ts is an industriall y meaning fu l target, since the cata lysts could be easily removed from the react ion mixtures and wastes could be largely di minished_ M onometalli c-supported catalys ts are 'vvidely used for thi s purpose, but bimetallic catalysts show growing attention, as the addition of a second metal can drastically improve the activity and/or se lect iv i ty towards the des ired product 17 M et<ds deposited on reducible ox ide Ti02 and Zr02 sho\-\! better catalytic behavior on the selecti ve hydrogenation of

chloronitrobenzene and (X,B-unsaturaleci aldehydes to unsaturated alcohol s5.7. ' 8-2.1 . lt is proposed th at th e

strong metal/support interact ion is responsible for thi s behaviour. The aim of the present work is to study the

NOTES 1647

hydrogenat ion properties of PtM/Zr02 catalysts (M =Cr, Mn, Fe, Co, Ni, Cu) on the hydrogenation of cinnamaldehyde.

Experimental Zr02 commercial support (AR, SI3ET= 113.4 m2/g,

tetragonal system) was crushed and sieved to obtai n a particle size range of 140-180 meshes. The monometallic Pt/Zr02 catalyst was prepared by conventional impregnation with an aqueous so lution of hexachlorop latinic acid . The content of platinum was 0.3 wt%. The impregnated sample was reduced by keeping it in contact with an aqucous soluti on of KBH~ at room temperature for 2 h (kecping the molar ratio of the rcducing agent to platinum meta l as 200), filtered with distill ed water, dried at 373 K overnight. The bimetalli c PtM/Zr02 catalys ts (M=Cr, Mn , Fe. Co, Ni and Sn ) were al so prepared by impregnation. The solut ion of" mctal nitrate is impregnatcd on Zr02, dri ed at 373 K, was calcined at 673 K for 4 h, and then platinum was impregnated . The preparation process was similar to that for Pt/Zr02.

Surface areas of the supported platinum catalysts were detcrmined by N2 adso rption at 77 K using the BET method in an OMNISORP 100CX apparatu s. Di spersion of platinum was measured by H2 chemi sorpti on 2~ . By assuming a stoichiometry for H2 adsorption on surface platinum atoms (PtJ of unity, the di spersion of Pt is given by D=PtJ Pt,=H/Pt,. The sizes of pl atinum parti cles were obtaincd by transmission electron microscopy (TEM) using a JEM-200CX apparatus . These results are given in Table I.

A typical hydrogenati on procedure is conducted as fo llows: the cata lyst ( 1.8x I 0 ) g Pt), I mL of

Table I - Charactcri zati on o f the rt/ZrO ~ catalysts"

Sample H/Pt" Mean panic le size I3 ET rrom TEM (nm) ( m ~/g)

Pt /ZrO! 0.80 2 .0 96.8

PtCr/ZrO! 0.7 1 3.5 80 .9

PtMn/ZrO~ 0.69 :U ; 79 .2

Ptre/Zr02 0.55 4 .0 76.8

PtCo/Zr02(0.04 ) 0.66 2.8 8 1.4

PtCo/Zr02(O. I ) 0.5 3 4 . 1 74. 8

PtCo/Zr02(0.1 5) 0 .48 5.2 65.0

PtCo/Zr02(0.2) 0 .46 6.3 59.2

Pt i /ZrO ~ 0.5 7 3.0 92.6

PtS n/ZrO~ 0.63 3.3 82 .4

"The amount o f trans iti on metal is 0 .1 wt%; "l3 y assuming a stoichiometry for l-\ ~ adsorptio n o n surface platinulll atoms (Pt ,) as unity. the di spersion o r Pt is givcn by D=Pt/ Pt,=H/Pt,.

cinnamaldehyde (8x 1 0') mol) and ethanol solution are added into a 50 mL stainless steel autoclave. Care must be taken that the whole system is protected under nitrogen before H2 is charged. H2 was introduced several times to replace nitrogen and the final pressure of H2 was 2.0 MPa. The hydrogenation react ion is performed at 343 K for 6 h. Chemical analysis of the products is performed by gas chromatography Perkin-XL, equipped with a FlO detector and SE-30 capi ll ary column. Reactants and products are identified by comparison with authentic samples. Biphenyl is used as internal standard. Several experiments using different amounts of catalyst were carri ed out in order to determine the diffu sion control region and eliminate mass transfer limitations during our studies .

Resul ts and discussion Hydrogenation of cinnamaldchyde is a complica ted

process as shown in Scheme I. The 1,2-addition of hydrogen gives the unsaturated alcohol, the 3.4-additi on gives the saturated aldehyde, anll !.4-additi on gives the enol , which isomcri zes into a saturated aldehyde. Subsequent hydrogenation of the C=C or C=O leads to the saturatcd alcohol. Transi ti on metal complexes have bee n studi ed widely as homogeneous catalysts for the hydrogenation of organic compounds. They have also been used as co­catalyst in a large variety of chemical reacti ons. The addition of the transition metal ions and metal complexes to the noble metal catalysts can considerably modu late both the acti vi ty and the selectivity of the catalysts. Table 2 lists the results of selective hydrogenation of CMA catalyzed by Pt/Zr02 catalyst modified by Cr, Mn, Fe, Co, Ni and Sn. From Table 2, we can see tha t adding small atnount of metals to Pt/Zr02 catalyst leads to different hydrogenation properties. The catalytic activities are all improved except the addition of Cr. Pt/Zr02 catalyst modificd by Ni , Sn and Cr shows beller yield of HCMA, and Pt/Zr02 catalyst modified by Co, Mn

Schcmc 1

1648 INDIAN J CHEM, SEC A, JULY 2006

and Fe shows better yield of CMO. PtSn/Zr02 catalyst shows the highest yield of HCMA (76.1 mol %), and PtCo/Zr02 catalyst shows the highest yie ld of CMO (90.8 mol %). T hi s is an inte res ting phenomenon, Fe, Co, Ni are elements of the sa me group, the properties of them are s imilar but the additions of them have grcat different influence on the hydrogenation of CMA over PtM/Zr02 catalysts. It has been demonstrated that supported platinum catalysts modified by tin have much higher se lec tivities for the hydrogenation of the aldehyde group than the unmodified one. It has also been suggested that in supported Sn-Pt catalysts , the Sn"+-carbonyl interact ion is respons ible fo r the increased Sc=o selectivit/s.2~. However, PtSn/Zr02 cata lyst reduced

Table 2 - Results o f the hydrogenati on of CMA over PtM/Zr02 catalys ts"

Catalys t Con ver- TOrh Yield of products (mo l%)" SJlln (S·I)X I O· ~ II CMA II CMO CMO Others (%)

Zr02 nil

Pt/Zr02 49.9 2.2 25.5 21.7 42.2 10.6

Pt/ZrO~d 3.~.5 u; 550 I 1.0 34.0 0

PtCr/Zr02 2 1,4 0.7 40.5 8.0 1.0 44.5

PtCrlZr02d 26,4 1.5 53.3 13.0 33 .7 0

f'tMn/Zr02 55.2 2.8 27,4 66 52.0 14.0

PtMn/Zr02d 6R.2 4.0 2 1,4 17.9 60.7 0

f'tFe/Zr02 88 .6 6,4 5,4 10.7 R3 .6 0 .3

PtFe/Zr02c 80.3 5.8 7.6 8.9 82.9 0 .6

PtFc/ZrO/ 98.9 7.2 0.8 27. 1 72.1 0

Fe/Zr02 r nil

FeB/ZrOl 19,4 1.0 6.5 18.2 75.3 0

PtCo/Zr02 90.2 6.8 3.5 5.7 90.8 0

PtCo/Zr02d 98.5 7,4 0,4 15.5 R4 .1 0

PtNi/Zr02 70.6 4.2 64.3 11.8 7.8 16.1

PtNi/Zr02d 96,4 6.8 62.8 36.9 0.3 0

PtSn/Zr02 6 1.4 3.3 76.1 1.5 6.6 15 .0

PtSn/Zr02d 76,4 4 .9 59.R 27.6 12.6 0

"React io n conditi on: 8x I 0" 11101 CMA; reac tion temperature is 343 K; P is 2.0 MPa: The amo ulll of catalyst is 0.6 g. The amount of metal is 0.1 wt%. "TOF, specific act ivit y pCI' Pt surface atom (S· I) for the hydrogenation of cinnamaldehyde over supported Pt catatlysts. "Some products with hi gh boiling point cou ld not be determined by GC analys is: HCMA=hydrocinn:lmaldchyJ e. HCMO=pheny l­propano l: CMO= cin namyl alcoho l. dReaction of hydweenat ion o f CMA over PtMIZr02 catal ys ts in the prescnce of I mg NaOH and I 1111 H20. "Catalyst was reduced by 1-1 2 for 2 h at 673K. "The catalyst of FelZr02 is prcpal'ed from Fe20 ,/Zr02 red uced by KDH~.

gThe catalyst of Fe13/Zr02 is preparcd from Fe(NO, lJ supported on Zr02 reduced by KBH~ solutio n for 24 h.

by KBH4 shows lowest yield of CMO on the hydrogenation of CMA in our studies. Similar phenomenon has also been reported eari Ier30. The presence of boron species is respons ib le for it. We have also investigated the effect of K and B. We find that K shows negligibl e effect. PtFe/Zr02 catalyst reduced by KBH -l shows better cataly:ic activity than PtFe/Zr02 catalyst reduced by H2. No products are observed when zirconia support is tested In cinllamaldehyde hydrogenation . Cnder reaction condition, Fe/Zr02 catalyst shows neg ligible cata lytic activity on the hydrogenation of CMA. FeB/Zr02 catalyst shows low ca talytic activity. It shows tha t the presence o f B is also a reason for good effec ts.

From Table 2, we al so find o ther products o n the hydrogenation o f CMA in ethano l over PtM/Zr02 catalysts except PtCo/Zr02 catalyst. These products are the formation of acetals. Thi s was confirmed by mass spectrometric measurements . T he formation of acetals is observed when pure alcohol is used as

solvent during the hydrogenat ion of CY.- ~-unsatura ted aldehydesS

..1 I. This reaction does not occur when a little water is present32 . In our expenments, we find that catalytic activities are il. lprovecl in the presence of NaOH. Similar results were also reported in the

I· 3,34 S .. d h patent Iterature·· ... 0, we Investigate t e hydrogenation properties over PtM/Zr02 catalysts in the presence of I mg NaOH and I mL H20 . These result s are listed in Table 2. From Table 2, we see that catalytic activity is improved in the presence of NaOH and H20. PtFe/Zr02 catalyst shows best conversion of CMA (98.9 mol %). P,Co/Zr02 catalyst shows the highest yield of CMO (84.1 mol %), and PtNi/Zr02 catalyst shows the highest yie ld of HCMA (62.8 mol %). We have not found acetals in our ex peri men t.

Pt/Zr02 catalyst modifi ed by diffe rent Co content also shows good catalytic properties for the hydrogenation of CMA (Table 3) . We see from the table that catalytic activity and yield of CMO are all ------------------------

Table 3 - ResullS of differenl Co amounl on Ihe hydrogenat ion of CMA over Pt/Zr02 calalyst"

Co Conver- TOF Yield ol~I'r,)(jucts (mol%) content sion (s· l)x IO·1 HCMA HC MO CMO Others (wt%) (%)

49 .9 2.2 25.5 2 1.7 42 .2 10.6

0.04 71.9 4,4 14.2 9.S 76.0 0

0.1 90.2 6.S 3.5 5.7 90.8 0 0 .1 5 94.3 7.9 2.2 9.8 88 .0 0

0.2 69.1 6.0 5.7 2.2 92.1 0 "Reacl ion condi ti ons similar to Ihose for Table 2: the amount of cata lyst 0.6 g. ----

NOTES 1649

improved remarkably with addition of Co to Pt/Zr02 catalytic system. No by-products are found. When the content of Co is 0.15 wt%, the PtCo/Zr02 catalyst exhibits the best conversion of CMA (94.3 mol%). Figure I demonstrates the relation of co nversion of CMA and selectivity to each product as functions of the reaction time for PtCo/Zr02 (Co 0.15 wt%) on the hydrogenation of CMA. The main products are HCMA, CMO and HCMO. The conversion of CMA increases monotonously with the react ion time, and the yield of CMA is always over 86 mol% during the reaction time. During the initial reaction time, the product of the hyd rogenati on for C=C is formed. As the reaction goes on, the yield of HCMA decreases, and the yield of HCMO increases. But, the yield of CMO almost remains constant , which indicates that deep hydrogenati on of HCMA is easi ly carried out. It shows that the two se mi-hydrogenated products (HCMA ane! CMO) are formed on dirrcrent surface sit es and the modifyin g effec t proposed above has di fferent influences on these ~ ites. More acti ve metal sites for the hydrogenati on of C=O of PtCo/Zr02 catalyst are res ponsible for the hi gher yield of CMO during the hydrogenati oll of CMA .1s .

As i ne!icated above. Pt/Zr02 catalys t modi fied by small amount of metal s (C r, Mn , Fe, Co, Ni and Sn) ex hibits different hydrogenation properti es for the hydrogenati on of CMA . Amo ng the catalys ts, PtCo/Zr02 catalyst ex hibit s the best catal ytic acti vity and yield of CMO. The efi"ect of metal may be usuall y interpreted by electronic effect and/or geomet ri c effec t. As reported in literature, good hydrogenati on properti es are found on large Pt particles. Such behaviour is al so reportee! by Gal vagno el 01 . .\(' for ci nnamaldehyde hydrogena ti on over Ru/C catalysts and Coq ef 01.'7 for 2-butenal hydrogenation over Pt/AI20 .1 catalys ts. Thi s behaviour is interpreted in terms of a transiti on state bearina a weak neaative

'" '" charge, which is effectively stabilized on the large Pt particles. Thi s interpretation cannot be completely appl ied to the present work as these Pt particles do not change markedly in size upon adding small amount of metal (Table I ). The other interpretation proposed by G I I I I· IX a vagno ef ({ .' and Richard el al .. ', suggests the deposition of electron deficient centers on the platinum surface, wh ich tends to adsorb C=O groups through the unshared electron pairs of carbonyl oxygen. Ionic and electron deficient metal speci es for PtM/Zr02 catalyst acting as Lewis acid that activate the C=O group towards addition of the hydrogen chemisorbed on the platinum. The different effect

::: <3

100 -,-~---,-~---,-~---'-~---r-~---'

80 '7~; .----_.=--1 ____ Conversion

---+-HCMA ~HCMO

~CMO

20 0_0 __ °== __ <.--.0'---1 a .... -. 023 5 6

Time (h )

100

'0' ~

80 g -=-J!)

60 ~ ~ 0.. .... 0

40 .~ . .., " u

20 u or.

0

Fi g. I - T ile conversion or CMA and Lile selccli vily to eac il pmduci as funcLi ons of lile rcaclion limc for PlCo/ZrO, (Co 0. 1.'\ IVL'k ) calal ys l.

may be related with the presence of [3 .,1) . .).) . FeB/Zr02 catalyst shows cel"tain catal yti c activ ity. Under our cat~1 l y tic preparation, cobalt boride. iron boride and nickel boride can form in the presence of aBH ~ .

These boron co mpounds also ha ve influence on hydroge nation properties on the hydmgenation of CMA . The good e ffects are al so related to the specia l nature of supported Zr02. The stron g metal/support interaction state of Pt/Zr02 is responsible for the gooc\ cata lyti c activity on the hydroge nati on of CMA.

Conclusions Pt/Zr02 catal ys t can catalyze the hydroge nati on of

CMA at 343 K and 2.0 MPa. Catalyti c activiti es are all i I11proved wi th the int roduc ti ons of small amount of metal to Pt/Zr02 catal yst except Cr. PtNi/Zr02 and PtSn/Zr02 catalys ts show better select ivity of HCMA, and PtCo/Zr02 and PtFe/Zr02 catal ysts show better se lectivity of CMO. The hi ghest yield of HCM A (76.1 mol%) is obtained for PtSn/Zr02 catalys t and the hi ghest yield of CMO (88 .0 11101%) is obtained for PtCo/Zr02 catalyst. In the presence of NaOH and H20, the hyd rogenation rate increases significantly and side reaction is remarkabl y inhibited. The main reason of good yie ld of CMO is that there are 1110re acti ve sites for the hydrogenatio n of C=O group on PtCo/Zr02 catalyst surface. The content of Co in Pr/Zr02 catalyst has signifi cant in !luence on catalytic properti es for the selective hydrogenation of CMA. Both catalytic activity and yield of CMO Increase with addition of Co to Pt/Zr02 catalyst.

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1650 INDI AN J CHEM , SEC A, JULY 2006

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