RuCo and IrFe Bimetallic Carbonyl Cluster-Derived Catalysts for Selectivity Controlling in CO Hydrogenation Towards C1-C3 Alcohols

A. Holmen e t al. (Editors),Natural Gas Conversion 0 1991Elsevier SciencePublishersB.V.,Amsterdam

RuCo and IrFe BIMETALLIC CARWNYL CLUSTER-DEKlVED CATALYSTS FOR SELECTIVITY CONTROLLING IN CO HYDROGENATION TOWARDS

Hasaru ICHIKAWAl*. F.-S. XIAO', C.G. MAGPANTY',

(:I-c3

ALCOHOLS

Atsushi FbKUOKAI, W.

HENDERSONZ, and D.F. SHRIVER2 'Catalysis Research Center, Hokkaido University, Sapporo O6O(Japan) ZDepart,mentof Chemistry, Horthwestern University, Evanston, 11 60201(U.S.A.)

SUMMERY The bimetallic catalysts prepared from SiOz-supported IrFe and RuCo carbonyl clusters exhibited high yields and select.ivit.iestoward oxygenates such as (:IC 5 alcohols from COtHz. In contrast, hydrocarbons and COz were preferentially obtained on the catalysts from the homometallic Ir, Fe, Ru and CO carbonyl clusters. The promotion towards alcohol formal.ion OH RuCo c.liist.er-derived catalysts was proposed to be associated with the adjacent,Ru-Cod* sites at the cluster-support interface to offer C- and 0-ended CO( vco=1680 c m - l ) which is The formyl species is hydrogenated to formyl intermediates(Y c0=1580 c m - 1 ) . converted eventually at 510K with Hz into CH30H and CH4. At higher temperatures t,he higher Cz-Cs alcohols are produced via CO dissociation and acetyl intermediates(vco=1555-1540 cm-1)formation from COtHz on the IrFe and RuCo cluster-derived catalysts. INTRODUCTION It has been previously reported that some electropositive ions such as Mn, Ti, Zr, Nb and Fe promote the production of oxygenates such as aldehydes and As a localized model alcohols in CO hydrogenation catalyzed on Rh and Pd(1). for the promoted Rh and Pd, tailored metal catalysts have been prepared from SiOz-supported RhFe(2) and PdFe(3) bimetallic carbonyl clusters as the precursors.

We have demonstrated that they provided higher activities and

improved selectivit.iw for CI and (:a alcohols from COtHz, compared from the homometallic cluster-derived catalysts and even those of the conventional bimetal catalysts. By means of EXAFS, Mossbuer and FTIR spectroscopies(4) it i s suggested that the effective catalysts contain the localized ensembles having a adjacent Rh-Fe3* and Pd-Fe3* which are active for the migratory C!O insertion toward the oxygenated products in CO hydrogenation(2,5). We extended to prepare the IrFe and RUCO bimetal r.at,alysts using series of bimetal carbonyl clusters impregnated with SiOz and study on the selectivity controlling of oxygenates such as alcohols as judged in CO hydrogenation. The surface intermediates in CO cheaisorption and COtHz reaction are investigated by In situ FTIR observat.ion using the isotope labelling tracers on the catalysts prepared from RuCo carbonyl clusters on SiOz. The origin of

298 promotion f o r Ci-C3 alcohol formation in CO hydrogenation is discussed in terms of the two-site activation of CO to offer the oxygenate intermediates formed on the adjacent RuCo and lrFe sites derived from the SiOz-supported clusters. EXPERIMENTAL For the Ir, IrFe and Fe catalysts various carbonyl clusters such as

(TMBA)[HI1-4(CO)11 3 , (TMBA)z [ FeIr4 (CO)is 1, (TMBA)[ FeI1 5 (CO)1 5 3 , (TMHA)[FezIrr(CO)is] and (NEt4 )Z[Fe3(CO)11] (where TMBA=NMe3CHzPh) were impregnated(2 wt% metal) with SiOz gel(Davison tiR 10303; S.A.=330 m2/g) from THF solution. After removal of the solvent the SiOz-impregnated catalysts were mildly oxidized by Oz at 300K. followed by reduction with flowing Hz at 6738 for 2 h.

The Ru, RuCo and Co cluster-derived catalysts were similarly prepared

by using precursors such as (EttN)[HRus(CO)ii], Ru6C(C0)17. H~Ru~CO(CO)~Z, RusCozC(CO)ir, RuCoz(CO)ii, HRuCo3(CO)iz and c04(co)12. The conventional salt-derived catalysts were obtained by coimpregnation of SiOz with EtOH solution of IrChHzO, FeC13, CoClz abd RuC13, followed with Hz reduction at 673K for 2 h. The pressurized COtHz reaction was performed wit.h a flow-mode stainlesssteel reactor(i.d.=14 mm; 240 mm long tubing). Oxygenated products were collected in a wat,er-condenser(50 ml HzO) by bubbling the effuent gas. Products were analyzed by TCD and FID gc using A.C.(lsl293K), DMF/AlzO3 (4m,273K) for hydrocarbons, CO and COz and Chromosorb 101(41n,408K) f o r oxygenates such as CHsOH, CzHsOH, CH3CHO and acetates. In situ IR studies were conduet.ed on a double-beam Shimadzu FTLR-4100 at a resolution of 2 cm-1, coupled wit,h QP mass-spectrometer(Anerva-200) to monitor the gas phase.

The IrFe and KuCo carbonyl ?lusters were impregnated on a

dehydrated SiOz disc using a dropper with the cluster solution inside I R cell with CaFz window under Nz atmosphere, which were oxidized by Oz and reduced with Hz at 673K. For the isotope-labelling experiments l3CO(90% enriched) and

Dz(99.9% purity) were purchased from MSD lsotope Ltd. RESULTS AND DISCUSSION

a Hydrogenat-i&n

on 1 rFe Rimetalljg CLii.stLer:Deriyd Catalms The results of 5 kg/cmz pressure CO hydrogenation are presented in Fig 1,

where the specific rates of product formation and selectivities are evaluated on mmol/min/(Ir m m o l ) in CO base.

It is interesting to find the CO conversion

at 523K and the rates of oxygenate formation were dramatically enhanced by a factor of over 300 times magnification on the Fe-containing Ir catalysts, compared with i.he Irs/SiOz

.

They gave higher select.ivitiestoward oxygenat.es mainly consisting of CH30H and EtOH (upto 76% sel), whereas the methane selectivit,ywas greatly suppressed. Part.icularly, it is of interest to find

299

Fig 1. Correlation between Rates of Product Formation in COtHz Reaction and Ir/Fe Atomic Ratios of the Catalysts using Various IrFe Carbonyl Clusters. CO:Hz=1:2 v/v, 5 kg/cd, 2500C

.-c 0 CHq

0

CzHsOH +CHnCH(

A C3H70H

I

Ir4 FeIrs FeIg

FeZIr,

I

SV=lOOO h-1 Catalysts: Precusors/SiOz ( 2 wtX metal loading) after Hz reduction at 673K Ira:[HIrs(CO)ii-] FeI1-5 :[ PeI1-5 (CO1 1 6 - ] FeIrr : [ FeIrr (C0)is 12Fez I r4 : [FezIrr (CO)1 6 12Fez I r2 :f FezI rz (CO 1 z ] 2 -

FezIrz

that C2+ alcohols such as EtOH and PrOH were produced in COtHz on SiOzsupported FeIrs, FeIrr and FezIrz catalysts at 523-5638 with the selectivities of 24-28%, although the Irr/SiOz catalyst had no catalytic activities for higher alcohols under the reaction conditions. The 2 wt% loading [Fe3(C0)ii2]/SiOz-derived catalyst was apparently inactive for CO hydrogenation. Since the cluster-derived catalysts on SiOz were prepared in higher metal dispersions regardless the used precursors, such a marked enhacement of CO conversion and higher selectivities toward alcohols on Fe-containing Ir catalysts are likely associated with the generation of IrFe adjacent sites possibly located at the cluster-oxide support interface active not only for CO dissoication but also f o r CO insertion. A similar promotion mechanism has been previously proposed(3,5) on RhFe and PdPe carbonyl clust.er-derivedcatalysts which

exhibited the substantial improvement of C1-Cz alcohol produckion in CO hydrogenation. The conventional IrFe catalysts prepared from coimpregnation of lrClr and FeC13 provided a poor yield and selectivity toward alcohols rather

than on the corresponding clust,er-derivedcatalysts.

The bimetallic lrFe

clust,er precursors offer the advantages for higher metal dispersion and uniform distribution of active lrFe sites over the conventional salt-derived catalyst preparation. RuCo - Bimetallic Cluster-Derived -. - -- Cataly&S Ln CO Hydroe;eEat&rj

The catalytic activity of SiOz-supported RuCo carbonyl cluster-derived catalysts reached the steady state of CO conversion and product selectivities orienting toward alcohols after 10-15 h on stream in CO hydrogenation, and

300

remained const,ant f o r subsequent 45-50 h. The specific rates and selectivities in 5 kg/cm2 COtH2 reaction after 15 h on various Ru. RuCo attd Co catalysts are presented in table 2. The Ru and Co catalysts prepared from [HKua(CO)ii ]/SiOz and €04 (CO)iz/SiOz provided t,he preferential formation of methane and higher hydrocarbons(Cz-CsI with poor selectivities of oxygenates(25% s e l in CO base).

In contrast, the catalysts from Co-containing Ru clusters

such as R u ~ C O , RuCoz, and RuCoa carhonyls impregnated on Si02 exhibited the marked Pnhancement of CO conversion(10-30 Lines higher in Ru base) and higher selectivities of oxygenates consisting of Cz-65 alcohols(l8-30% sel in CO Table I . Catalytic Performances of Ru, KuCo and Co Carbonyl Clust,er-Derivpd Catalysts in CO Hydrogenation: CO/Hz=0.5, 5 kg/cmZ, 523K, 1000 h-1

__~__

.______.__

-

-__-

catalyst. CO conv specific: ratx of formation(mol/min/mol(Ru) select,ivity precursor/SiOz ( % I hydrocarbon' oxygenates** of oxygenates c1 c z c3 c 4 CS 61 c 2 €3 c4 €5 (%I (2 wt% metal) __

~

-

-

-

0

5

0.8

0.2

-

14

4.8

12

0.7 0.2

0.1

13

12 12

15 0.9 11 1.5 6 0.8

0.5 0.3 0.3 0.1

10 18 38

[HRu~(CO)II]0.3 16

I

<1


-

-

H~RU~CO(CO)IZ 2.5 50

8

9

4

4

3.4

4 . 4 110

12

13

7

3

HRuCoa ( CO I 12 523ti 9.8 240 31 498K 4 . 7 99 1 3 45816 1 . 3 24 3

31

18 7.5

2

12 7.5 2

RiiCoz(C0)11

14

3

10

-

0.8 0.5

RuC13tCoClz

2.2

46

5

7

6

4

0.7 <1

(1

-

-

3

CO4(Co)lZ

0.1

5

1

-

-

-

0.5 t

t

t

-

<1

*

hydrocarbons; CI :CHr, Cz :CzHstCzHr, C3 :C3HstC3H6, €4 : C 4 H i 0 , C5 :C5Hi2 **oxygenates; Ci :CH3OH, CZ:C,~H~OH+CH~CHO, C3:C3H70H1 C~:C~H~OH,CS:C~H~IOH The oxygenate se1ec:tivit.ie.sare not sensitive to Ru/Co rat.ios in the base). catalysts, but essentially based on the RuCo moieties as the catalyst. precursors.

Again, it. is found that t.he RuCo carbonyl clusters offer

effective advantages f o r higher CO conversion and alcohol selectivities over the conventional salt-derived catalysts. Using CO-rich syn.gas(CO/Hz=l-2 v/v) t.heoxygenate selectivities on RuCoa/SiOz were further improved to 38-45% sel in 2-3% CO conversion due t o suppression of hydrocarbons. The yields of hydrocarbons and Cz+ oxygenates on the RuCoa/SiOz catalyst at 523-563K obey the Schluz-Flory distribution in terms of carbon numbers similarly those on t.he typical FT reactions(6).

In __ situ

__ FTIR Studies

1)C- and 0-ended CO chemisorbed on the RuCo catalysts As shown in Fig 2, upon C:O admission at 300-3448 onto the freshly reduced Ru~CozC(CO)ir/Si02 and HRuCos (C0)iz the two absorption bands at 2072 and 2036

cm-'(lineer CO) and I960 cm-l(bridge (XI) on Hu were observed.

Moreover, a

301 low-frequency band a p p e a r s a t 1680 cm-1, which s h i f t s t o 1640 cm-1 w i t h t h e RuCo c a t a l y s t s d u e t o t h e 'SCO i s o t o p e e f f e c t .

13CO

on

The p a r i c u l a r CO b a n d s

were also o b s e r v e d a t 1680-1684 rm-1 on KuCoz/SiOz, b u t n e g l i g i b l y on Rus(:(CO)i?/SiOz a n d Co4 ((:Oliz/SiWz -derive11 c a t a l y s t , . CO o c c u r r e d o n t h e c o n v e n t i o n a l Kh-Mn,

A low f r e q u e n c y band of

Kh-Ti a n d Rh-Zr/SiOz(lc,Gl

which are

a c t i v e f o r o x y g e n a t e f o r m a t i o n i n CO h y d r o g e n a t i o n , where a l a r g e r e d u c t i o n o f t h e CO frequency(1730-1620 em-')

was i n d u c e d .

F i g 2. FTlR s p e c t r a i n CO chemisorpt i o n a t , 300-340K o n RusCozC(CO)ic/SiOz afi Hz r e d u c t i o n a t 67K, 2 h

2072

S h r i v e r et. a 1 . ( 7 ) demonstrated

F i g 3. I n - s i t . u PTlR s p e r t r a i n COtHz R e a c t i o n o n RuCo a n d Ru r l u s t e r - d e r i v e d c a t a l y s t s CO/Hz=0.5 v / v , l atm a t 453K f o r 4 h

I

"CO (IOOTorrl

C O + H ~on R ~ ~ C I ~ C C O I ~ J S ~ O ~ (

precursor : C o z R u ~ C ( C 0 ) 1 ~ / S i 0 z

2020

h204'"

"CO (I00 Torr)

l2CO (I00 Tom)

t h a t t h e s t o i c h i o m e t . r i r format.ion o f a d d u c t s bel.weei1 metal c a r b o n y l s s u r h as

Fez(C!O)s a n d RU4(CO)lZ and L e w i s a c i d s s u c h as A l C l : j ,

BF3

andi-AlzO3 arises

from C- a n d 0-bound C:O r h a r a c t e r i s t i c of b a n d s a t 1740-1520 rm-l, and t.he r a t . e o f methyl m i g r a t i o n , i . g . CO i n s e r t i o n , t o form t h e a c e t y l complex i n Mn(CH3 ) ( C O ) 5 is g r e a t l y enhancpd by t h e a d d u r t format,ion w i t h A 1 h - 3 a n d HF3. By comparing t h e FTIR d a t a w i t h t h e s t r u c t u r a l model of t h e bimetal r l u s t e r -

d e r i v e d cat,alyst.s(1,3,5)it is c o n c e i v a b l e that, t h e RuCo sites i n the c a t a l y s t s g a v e t h e t.wo-site CO a c t i v a t i o n a l i k e [Ru-C=O--Co]. 2)Formyl I n t e r m e d i a t e s i n C O t H z reac.t,ion When t h e c a t a l y s t s s u c h as RuaCozC/SiOz a n d RuCoj/SiOz were h e a t e d from 3OOK t o 423K t,he b a n d s at, 2070 cm-1 o f l i n e a r CO s h i f t e d t.o 2020 cm-l, a n d t h e

p a r t , i c u l a r band a t , 1680-1684 cm-1 c h a r a c t e r i s t i c of C- a n d 0-bound CO g r a d u a l l y d e c r e a s e d and a new band a p p e a r e d a t . 1580 cm-l( 1575 r m - I i n I.he r e a c t i o n w i t h D z ) which was d e v e l o p p e d i n time. f l o w i n g HztCO(2:l v / v ,

The i n s i t u FTlR s t u d i e s

by

1 atm, 40 ntl/mjn) at, 423K showed 1.he i n t e n s e b a n d s a t

1580-1584 c 1 n - ~ ( 1 5 4 6c m - 1 by IJCOtHz) o n t h e RuCoa/SiOz, RuCoz/SiOz a n d

302

RuaCo/SiOz catalysts, as shown in Fig 3. There is a good correlation bet,ween the yields of Ci-C5 alcohols in CO hydrogenation and the band intensities at 1580 cm-1 on the catalysts from t.he different RuCo carbonyl clusters on SiOz, as shown in Table 2. The particular band around 1580 cm-' could not observed Table 2. Rates of Formation f o r Fig 4 . Possible Mechanism of oxygenates and Intensities of 2020, fornyl Intermediates from 1880 and 1580 cm-1 Carbonyl Bands Two-site CO Activation on on the Catalysts Prepared from Various RuCo Cluster-Derived Catalysts Cluster Precursors

precursors

on silica

intensitm:(A)

m20

of bands at 1880 1584

0.33

0.038 0.045

Irm-~l

TOF oxygenate? in COtHz Reaciion hnal/mol(Ru)min)

0.035 0.050 I

..

mT0-0-0-0m;r o : Intensities of adspecies of CO t Hz lCO/Hz-O.5) M RU-Co/SiOz

for 10 hours at 453 K . b: Rate of oxygenate formation ZiCl at 498K, I atm, 100rni/min

[i-l-5),

mtoiystr

inCO+HZ [1:2) reoctim

on the Rus/SiOz, RusC/SiOz and Corl/SiOz under t.he reaction condit,ioris. Besides the band at 1580 cm- there appeared the weak bands at 2860-2932 cmpossibly due to C-H stretching vibration and a minor peak at 1377 cm-I on the RusCozC/SiOz and RuCoa/SiOz catalysts in COtHz reaction. From these IR studies using the lZC0 and Dz we propose that the band at 1580 em-' could be assigned to C=O stretching of forrnyl :HC(=O), which is resulted from hydrogenation of' the C- and 0-eded CO on the adjacent RuCo sites as shown in Fig 4. Some analogous IR bands due to formyl coordination have been reported in Os(CHO)(H)(CO)z(PPhs) (vc0=1601.~~-~=2760 cm-l), Re(Et)(CO)(NO)(CHO)(vco=l624 cm-1) and Li+(CO)sReRe(CO)(CHO)(vco=1529 cm-')(8). The C-H band of CHO species is too weak to detect by IR. The minor peak at 1377 cm-1 which missed in 13COtDz and COtDz reaction could be associated with the deformation vibration of CHz in3formyl bound to the KuCo sites, similarly proposed by EELS study on Pd(111)(9). The proposed formyl species due to the 1580 cm-1 band reacted with 100 torr of Hz or Dz gave a mixture of methanol and methane at 423-473K on the RuCoa/SiOz catalyst. Mass analysis of the gas phase (Fig 5) suggested that the formyl species from COtHz is converted with Dz pinly to CHDzODtCHDs. At higher temperatures above 423K the yields of higher Cz+ alcohols substantially

303

increased in COtHz reaction on various RuCo catalysts, as shown in Table 1. It is interesting to find in the 1R study that the band at 1580 cm-1 was gradually decreased and two new bands at 1540 and 1550 cm-l were developped in time-on-stream, where Cz-Cs alcohols were detected in the gas phase by gc-mass analysis. These results suggested that the two-site CO activation on the RuCo sites results in CO dissociation at higher temperatures in formying alkyls, which is further inserted with CO to make higher carbon oxygenates such as CzC5

alcohols in CO hydrogenation on the RuCo ratalysts, as proposed the

mechanism in Fig 6. Fig 5. Mass analysis of Pr0durt.s Formed by Reaction of Surface Species in COtHz Reaction wi1.h Hz or Dz at 473K f o r 30 rain. a1 background 0-s Tarr

Fig 6. Proposed Mechanism for Methanol and C Z - C ~Alcohol formation in CO Hydrogenation on the RuCo Adjacent sites

Cur: HWCuslCOt~/Si02 COtHz(1: 21 I otm. 473K, 2 h a f t u nucualion

I0 I2 14 16 18 20 '25 27 29 31 33 35

bl

I

Rcacsrian with 01 at 473U 30 rnin

10 I2

14 16 18 20 W 27 29 31 33 35 Mars rumbrr (cm-'t

I

'

rmk-cd'm

IHz

IHz

ACKNOWLEDGEMENT The authors are great,ly indebted t o Dr. A. Fumagalli, Milano University to gift 11s some crystals of IrFe carbonyl clusters f o r the catalyst preparation. Thp part of this work is financially supported by the JSPS-NSF grand-aid f o r 1989-1990 US-Japan research cooperat.ion. REFEKENCE 1)a.M. Ichikawa, T. Fukushima, and K. shikakura, Proc. 8th Intnl. Cong. Catal.,vol II-69(1984) Berlin b.M. Ichikawa, and T. Fukushima, J. Phys. Chem., __ 89, 1564(1985) c.T. Fukushima. K. Araki, and M. Ichikawa, J.C.S. Chem. Commun. ,148(1986). 2)a.A. Fukuoka, M. Ichikawa. J.A. Hril.jiac, and D.F. Shriver, Inorg. Chem.,=, 3643(1987) b.A. Fukuoka, T. Kimura, L.-F. Rao, and M. Ichikawa, Catal. Today, 5 , 55(1989). 3)a.T. Kimura, A. Fukuoka, A. Fumagalli, and M. Ichikawa, Catal. Lett., 2, 227(1989) b.M. Ichikawa, A. Fukuoka, and T. Kimura, Proc. 9th Intnl. Cong. Catal.,vol 2-569(1988) Calgary. 4)M. Ichikawa, T. Fukushima, T. Yokoyama, N. Kosugi, and H. Kuroda, 3 . Phys. Chern.,90,1222(1986). 5)M. Ichikawa, Polyhedron,T., 2351(1988). 6)W.M.H. Sac:htler.and M. Ichikawa. J. Phys. (:hem.,@, 1752(1986). 7)C.P. Horwitz, and D.F. Shriver, Adv. Organomett.. 219(1984). 8)a.J.A. Gladysz, and W. Tam.,J. Am. Chem. soc.,~,5114(1979);Chem. Commun.,530(1979) b.K.L. Brown e t . al.,J. Am. Chem. S O C . , ~ ,505(1979). 9)J.L. Davis and M.A. Barteau, J. Am. Chern. soc.,j_l_l.,1782(1989).

,a,