Characterization of catalysts prepared by adsorption of phosphorus and rhodium complexes on H-ZSM-5 zeolites

Catalysis Today,6(1989)123-132

123

Elsevier Science Publishers B.V.,Amsterdam-PrintedinTheNetherlands

CHAR4CTERIZATION OF CATALYSTS PREPARED BY RHODIUM CXXlPLJXESON H-ZSM-5 ZEOLITES A.RAHMAN, S. BbXELLE, A. ADm,

G. LEWYandS.

Department of Chemical Engineering and QuCbec, Canada, GlK 7P4

ADSORPTION OF

PHOSPHORUS AND

KALIAGUINEt

CiRAPS, Universite Laval, Ste-Foy,

Organometalliccomplexes containing Rh,

P and

Rh-P were used to perform

chemical modifications of ZSPI-5by the gas phase adsorption technique. Phosphorus is

responsible for

strong poisoning of the

acid sites both in the

presence or absence of rhodium. Quantitative analysis of IR

spectra of ad-

sorbed. pyridine indicates progressive poisoning of Bronsted acid sites by phosphorus. Independent TPD of smmonia measurements agree very well with the IR of

pyridine results.

ESCA analysis allowed the calculation of extrapar-

title and intra-pore-latticecontents of Rh and P using SPS intensity ratios. Rates of

olefin and

aromatic production during methanol to gasoline tests

(PUG) were found to be in good correlation with the

level of

Bronsted acid

site poisoning.

Ih-l'RODUCTION The

use

of

metal complexes in the chemical modification of ZSM-5 type

zeolites has attracted much attention over interest

the past

few years.

Particular

has been focused on the preparation of bimetallic clusters supported

on ZS?l-5using various preparation techniques. In

our previous work (1,2),

Fe, Pd, Ru and Rh loaded ZSM-5 catalysts r;erestudied for their deoxygenation activities, The corresponding samples were prepared by calcining dry homogeneous mixtures of the

zeolite and a metal comples in static air.

Some work

related to the structural and catalytic properties of rhodium loaded zeolites (3-11) and some other work dealing with the poisoning of acidic sites of ZSM5 zeolites with phosphorus are reported in the literature (12-18). To date, almost no information is available on the respective roles of Rh and P

supported on

ZSM-5, when both compounds are present simultaneously in

the catalyst. In the present work, we wish to report the preparation of Rh-P loaded 291-5 by gas

phase adsorption (CPA) of the RhCl(cO)(PhoP)z complex.

For comparison FWZSM-5 catalysts were prepared, using rhodium acetylacetonate Rh(CsH702)J, and P/ZSM-5 catalysts were phosphine P(C6H5)a, using the

0920~5861/89/$03.50

obtained utilizing triphenyl-

GPA technique in both

cases.

0 1989ElsevierSciencePublishersB.V.

Structure and

124 acidicity characterization by ESCA, ammonia were performed,

Methanol to

XRD, IR of adsorbed pyridine and TPD of gasoline (MTG) and n-pentane cracking

reactions were carried out to monitor the acid catalytic properties.

JZPERIt"fEVrAL Catalyst preparation ZSM-5 samples were synthesized according to a method designated as method B' by Gabelica et al. (19) and activation was performed by repeated ion change with

zeolites from two batches were utilized as supports for the They are designated in

lysts.

ex-

NHrNOJ solution followed by calcination in air at 500°C. ZSM-5 various cata-

this paper as H-ZA and H-2B with respective

Si/Al ratios of 41 and 38 as determined by atomic absorption (18). Table 1 gives the phosphorus loadings of samples Pl-P5/H-ZSM-5 prepared by GPA of

tri~enyl~osph~ne

in conditions described in reference (18). The

weight percentages of rhodium and phosphorus in samples C, D, well as

the complexes used in

E and

F, as

their preparation (20) are also reported in

Table 1. All Eh and p loadings were determined by atomic absorption. Table 1. Nomenclature and composition of catalysts Catalyst

Weight percent

Complexes used in preparation

Eh Pi/H-2.A P2/H-ZA P3/B-ZA P4/H-ZA P%/H-ZA c (l&/H-ZBf D (Eh'H-W) E (Eh-P/H-ZA) F (Rh-P/H-ZB)

P 0.30 0.40 0.70 0.80 2.40

Tm, TPP TPP TPP TPP BAA

4.27

EAA

4.42

RCI?I?P

4.3

2*44

FCTPP

4.03

2.25

RA4 = Rhodium acetylacetonate; IXX'PP= Rhodium chlorocarbonyl triphenylphosphine; TPP = Tripheny~phos~ine. H-W = ZSM-5 with Si/Al = 41, H-28 = ZSM-5 with Si/Al = 38. Catalyst characterizam Z%D S-ray diffraction patterns were obtained on a Phillips spectrometer using the CuEa ray excitation. Crystallite sizes were estimated for catalysts C, E and F

from the half-width of the rhodium line (28 = 40.8' for rhodium metal.

and 28 = 34.1' for F&Q equation (21).

in ealcined catalysts), using

the Debye-Sherrer

With calcined catalysts the average diameter of Rhz&

micro-

125 ~rySts.I~was

found to be 182, 90 and 80 A for sampIes C, E and F respective-

ly. For the

same catalysts submitted to

a two

hour MIY: test the rhodium

metal particle diameters were determined as 134, 239 and 197 A respectively. a XPS measurements were performed using a VG ESCALAR Mark If electron spectrometer. MgKa X-ray (BE) values were

radiation (1253.6 eV) was

obtained with

a

used.

All binding energy

precision of +O.l eV and Sit* line at

103.4 eV was used as an internal standard for

a charging correction factor.

XFS intensities were calculated by integrt\tingpeak areas after proper base line substraction. IR of adsorbed nyridine Thin self supporting wafers (roughly 6 mg) of the catalysts were calcined in situ

in a

quartz-Pyrex vacuum cell at 400°C under vacuum flO-6 Torr) for

20 hours. After cooling to room temperature pyridine vapor was admitted into the system for 5-10 minutes. Afterwards, the cell was degassed and evacuated (10-c Torr) at 200°C for 16 hours to spectra were

recorded both

eliminate physisorbed pyridine. AU

before and

digilab FTS-60 spectrometer with

after pyridine adsorption using a

2 cm-1

resolution in

the

range 4000-

1000 cm-'. TPD of ammonia TF'Dexperiments were carried out usirg a thermobalance (m

10-8 Setaram)

combined with a symmetric furnace and a RT 3000C Setarsm temperature controller. About 0.1 g of catalyst was preheated at 5OO'C for 2 hours under vacuum (IO-3

Torr).

The

from Linde) ws monia

hT&S

catalyst was cooled to

8O'C and

ammonia (99.99% anhydrous

introduced into the system for 1 hour. The physisorbed am-

evacuated under vacuum for 30 minutes.

Thermodesorption was ear-

ried out at a heating rate of S"C/min from 80°C to 500°C. Catalytic tests Hethanol to

gasoline fKfG) reactions were

performed in a microoatalytic

fixed bed reactor at atmospheric pressure and 400°C.

Methanol

(99.99% pure

from Fisher) was injected with flowing helium (30 cm$/min) for two hours into the reactor and a constant WSV

of 1.4 hr1

was maintained for all runs.

Ssmple collection wss achieved at 15 minute intervals during 2 a 16

hours

using

loop heated sampling valve (VAl.5?]equipped with a sequence programmer.

.Analysiswas performed by gas chromatography 1201.

RESWLTS A&D DISCUSSION

IR of adsorbed nyridine and TPD of ssmonia IR spectra of adsorbed pyridine for all samples show bands at approximately 1646 cm-1

(Bronsted acid

sites) and

1457 cm-1 (Lswis acid sites). The

126 estimation of

tB) and Lewis {L) acid sites concentrations fS-Ollt

the Bronsted

these IR spectra was done using an adapted version (18) of the

method ori-

ginally proposed by Rhea et al. (22): B

A8

-

z

-

L

x

(1)

(EL/fB)

AL

For the purpose of the calculations, the following assumptions were made: (a) Lewis acid

sites, observed in the

IX spectrum of pyridine adsorbed on

291-5, are formed during calcination by dehydroxylation and two Bronsted sites are destroyed for each Lewis site created. Thus for the supprt: &

=

2.27 - XLZ (for H-Z%)

(2)

Bz

=

2.46 - ~IXJ(for H-ZF)f

(31

as the numbers of Al atoms per unit cell are 2.27 and 2.46 for H-ZA and H-ZB respectively. If one applies Eq. (1) to the support, another equation between B8 and Eqs. (2) and &

La is obtained which is solved simultaneouslywith

(3) to

obtain &

= 1.8, and

L

= 0.26

for

H-ZA and

= 1.6, LL = 0.43 for H-ZB respectively.

(b) For P

containing samples it is assumed that one P is exchanged for one

Bronsted acid site: (P) =

Bz-B

=

Bz - (2.27 -

Bz)(EL/EI~)(AB/AL)

(4)

and that for Rh containing samples, one Rh*+ cation is exchanged for two Bronsted acid sites: Bz - (EL/EB)(AB/AL)Lz (5)

(=I1 = 2 (1.+ (EL/%)(AB/AL)I

where (P1 and (Rh) represent the number of phosphorus and rhodium containing ions per unit cell respectively, It was also PM*

ion constitutes one

Lewis acid

assumed that one

site whereas no such site appears

upon exchange with phosphorus. (C) As seen in Table 3, samples C and D, containing only Rh, show only minor amounts of

Rh8+ cations exchanged with the Bronsted acidity. For sim-

plifying the calculation procedure, it was therefore assumed that

only

P

is exchanged with Bronsted acid sites when both Rh and P are present in Table 2. Quantitative analysis of IR of adsorbed pyridine and TPD of ammonia for phosphorus containing samples m of tmeunis IS? 0T adaorbed pn-idin Icalculated CatJswst

XP btlk

P,“.C.

usiniz eq.

B,“.C.

4I vtx

P .m*.

P,“.C.

IReSldua‘l )

1.8 1.6

H-U

H-ZB porn-24 *m-u wm-24 PWH-ZA F5,11-2. U.C.:

0.30 O.‘O 0.70 0.80 2.90 unit

cell

0.38 0.53 0.55 0.57 1.53 of

the

1.42 1.27 1.24 1.23 0.21

ZM-5S"Pp)rt

B,U.C. f~esidmll

vtx

P erch

2.22 N.I. 0.20 0.28 0.30 0.31

0.82

0.18 0.52

*.‘I, 1.70

0.94 0.56 1.56

1.28 1 .a 0.56

0.26 0.283 0.51 0.30 0.85

127 the

catalysts tE and

of the IR of

F).

Table 2 represents the quantitative analysis

adsorbed pyridine and the TPD of

Progressive poisoning of acid sites with P is ob-

containing samples.

served as bulk P content is poisoning as

ammonia for phosphorus

measured by

increased.

Interestingly,the severity of

the remaining concentration of Bronsted acid

sites is identical for sample P5 and for sample E in Table ples contsining 2.4 wt%

bulk P.

contain a significant number of residual Bronsted acid ison with

samples E

and F.

3, both sam-

As shohn in Table 3, samples C and D sites in compar-

It is therefore reasonable to believe that

almost only P is exchanged with acid sites when both Rh and P are simultaneously present in the catalysts (E and F). The good

agreement between the IR and TPD measurements (except the measu-

rement of exchanged P in sample P3) suggests the validity of assumptions made in the

IR of pyridine calculations. The advantage of TPD of aknnoniaover IR

of pyridine is that no assumption is necessary to evaluate the Bronsted acid sites concentration in this case. Table 3. Quantitative analysis of IR of adsorbed pyridine for Rh and Rh-P containing samples calculated from eqs. (4) and (5) Rh*+/U.C*

Catalysts

c

0.15 0.05

D E F U.C.

P/U*C.

1.52 1.00

Blu.c. (Residual) 1.3 1.7 0.28 0.6

wt% P exch.

wt.%Rh exch.

0.26 0.09 0.82 0.54

: unit cell of ZSM-5, H-U = AL.27 Si93.73 0191 H-2.B= A12.46 Sis3.5, 0192

Photoelectron spectroscopy Table 4

presents ESCA data for P containing samples. An estimation of

ratios of atomic concentrations in the first layers of the using the model of

samples was made

a homogeneous solid as described in previous publication

(18). A more realistic treatment of ESCA

intensity data

the results are also reported in Table 4.

In this treatment, using the model

was also

made and

described in ref. (23) and ESCA data for unground and ground samples of each catalyst, the

surface segregated fraction of

the phosphorus located on the

external surface of the support (wt% x2, crystallite size Cz)

and the well

dispersed fraction within the pore lattice (wt% xl, crystallite size G f were calculated. Figure 1 compares the wt% P in the pore lattice

(x11 with that

exchanged with Bronsted sites determined from IR of adsorbed pyridine. At low

bulk loading (up to 0.6% as seen for samples Pl-P4) the agreement is very

good, which

suggests that almost all phosphorus species having penetrated

128

into the

pores of catalysts Pl-P4 are exchanged with Bronsted acid sites. A

different result is observed for sample E containing 2.4 wt% P. in Figure

1 that

for this

Onecan

see

sample, the value of xi is almost 3 times higher

than % P exchanged with acid sites. This is in accordance with our previous findings i20) that at

high P loading a large fraction of the pore volume is

plugged with phosphorus oxide. Table 4. ESCA data for P containing calcined samples (P/Si) x Catalyst

Bulk

PI/H-ZA PZ/H-ZA PJiH-ZA P4/H-2.A

Calculated using the model described in ref. 123)

103

p2P (evt

136.1 136.1 136.2 136.1

ESCA

6.0 8.2 13.9 16.0

10.9 19.2 25.9 25.7

(2%)

Z%,

Cl (A)

C* (A)

0.20 0.29 0.34 0.33

0.10 0.11 0.36 0.47

3 3 3 3

233 267 307 397

Tables 5 and 6 represent the quantitative treatment for Rh and P particles respectively using

the same models as in the treatment reported in Table 4.

For calculation purposes, Cl values were chosen between 3-10 B,and only those values yielding calculated CZ

values in good agreement with XLBA calculated

average crystal size values are reported in Table 5. good for

sample E,

This agreement is not

where (IRh/Isi)VPS value is higher than those of both

samples C and F for which it is very good. A lower value of CZ

is obtained

with sample E, which may have been the consequence of a slightly higher cal&nation temperature of sample F calcined F

sample.

causing more Rh2Cb

From the Rhld 52

agglomeration in the

binding energy values it is concluded

that rhodium is reduced to the metallic state at stedy state PITGoperation.

WTX

P IN THE

PORE LATTICE

(X11

Figure 1. Wt% phosphorus in the pore lattice {XI) calculated from ESCA data as a function of wt% P exchanged with Bronsted acid sites determined from IR of adsorbed p_yridine.

129 Table 6.

KSCA data for I#, Rh-P containing ssmples

310.1 309.9 309.7

135.0 134.8

26.7 E

rxb.I.=X1

+u

: F Si

sr, i -

.

b3*5 36.3

28.8

306.7 301.3 307.1

:z:

.

3*” 3.12 3.03

0.55 1.19 0.97

I3 5

131.6 EA.3 m9.9

5I.? 32.1 25.3

0.76 D.Jf 0.21

0

Table 6

gives similar results for the phosphorus particle size estimation

in samples E and F.

Sample E shows only a minor fraction of surface segrega-

ted Phosphorus {0.16% over a bulk 2.4% value) dispersed as a monoatomic layer (the numerical result of C&=0.3 A indicates a CZ/ x << 1 situation). Similar interpretation follows from the results obtained with sample F which shows no difference in

zp/Isi 2~) ratio before and after grinding. Such

(IP

corresponds to

a result

the hypothesis of a homogeneous distribution of crystallites

within the pore lattice of the support. This hypothesis is the basis for the Kerkhof and

Moulijn model (24). However the (1~ 2p/I~i aPf ratio calculated

from this model for sample F oxide is 0.063. perimental

assuming monolayer dispersion of phosphorus

A value of Cl can therefore not be estimated from the ex-

value

of

0.095

because

this

model

predicts

only

fIp/Is~cl/~I~/Is)ocaolavcr< 1. It is

however clear

that in this sample phosphorus is well dispersed and

not surface segregated. Table 6. Quantitative treatment of XPS data for calcined samples 1IP

Catalysts

2p/ISi

Calculated for P using model (ref. 23)

*p)XPS

XB

(ut%P) E F

2,40 2.25

Unground sample 0.213 0.095

Ground sample 0.084 0.095

Cl (A) 2.24 2.25

0.16 -

3 -

c2

(81 0.3 -

Catalytic tests Figure 2 shows the proportion of products collected in a

lysts, as a function of the unit cell

propylene in

the

C3

fraction of the

MTG test for samples of Rh, P and Rh-P/HZSM-5 cata-

number of

unexchanged Bronsted acid sites per

estimated from IR of adsorbed pyridine results. The yield of pro-

pylene increases dramatically with the decrease of the

number of

acid sites

and eventually tends to become 100% when all acid sites are poisoned by phos-

130 phorus.

For'sample C, the point does not fall on the curve suggesting that

the produced olefins leaving the pore are hydrogenated on the

rhodium sur-

face. The increase in olefin production with poisoning is correlated with the decrease in aromatic and

O-GO

paraffin production as

shown in

Figures 3

and 4 respectively. Figure 5 shows the carbon number distribution of the

Figure 2. lilly; tests - weight percent propylene in C3 fraction a5 a function of Bronsted acid sites per unit cell products of

Figure 3. MTG tests - production of G-C10 aromatics (g/g CH3OR) as a function of Bronsted acid per unit cell

the standard MTG tests for samples H-ZSM-5, E and P5.

The simi-

lar activity with respect to olefin and aromatic production for samples E and P5 is the IR fold:

evidence for

equal levels of Bronsted sites poisoning as discussed in

results section.

The

effect of

rhodium in

the MlYi tests was two

some olefin hydrogenation is observed in the experiment involving

catalyst C as discussed above and some methanol decomposition was found to be dependent on metallic rhodium surface area (20).

1

Figure 4. MIG tests - primary production of CZ-CIO paraffins (g/g C&OH) as a function of number of Bronsted acid sites per unit cell

Figure 5. MTG tests - distribution of carbon numbers in the hydrocarbon products

131 cONCLUSIONS The following conclusions can be drawn from this-work: (1)

When ZSM-5 is modified by interaction with chlorocarbonyl bistriphenyl pbosphine rhodium, a significant poisoning of observed and

this effect

Bronsted acid- sites is

is analogous to the decrease in Bronsted acid

site concentration observed upon interaction of triphenyl phosphine with the same

zeolite,

tily

minor poisoning is obtained when rhodium is

introduced by adsorption of rhodium acetylacetonate even though last case

in this

large loadings of rhodium are present in the pores of the

zeolite. (2) Measurements of Bronsted acid sites concentrations can be

properly made

from the determination of ratios of absorbances at 1546 and 1457 cm-l in the IR spectra of pyridine adsorbed on the catalyst and This data

on the support.

treatment involves a set of stoichiometric hypotheses, the

validity of which has been

confirmed by

independent temperature pro-

gramme desorption of smmonia from the catalysts under study. (3) XPS qusntitation procedure described previously (18,20,23) and applied in this work is an effective tool in the determination of the structural features of both the supported phosphorus and the supported rhodium. In the present work it was found that when

triphenyl phcxsphine interacts

with H-ZSM-5, at low P loadings the amounts of phosphorus within the pores are

almost identical with those of phosphorus in cationic form

having exchanged protons.

The remainder of the phosphorus is surface

segregated. At higher phosphorus content finely dispersed oxide is also present in

the pores.

When phosphorus is introduced as a phosphine

ligand of a rhodium compleae, almost no phosphorus is surface segregated suggesting that the inward diffusion of rhodium facilitates the penetration of phosphorus. Interestingly some rhodium is surface segregated in the calcined sample and

after a

Ml% test.

These two results suggest

that outward diffusion of rhodium leading to

surface segregation and

sintering happens during calcination. (41 MTG tests confirmed the progressive poisoning of acid sites by phosph~rus.

Rhodium which is reduced to the metallic state in these tests has

two minor effects namely olefin hydrogenation and methanol decomposition. When phosphorus is present as high loadings of

intrapore lattice

oxide, the pore plugging effect associated with decreased methanol diffusivity in the pore lattice yields higher G-C4 duction of aromatics and paraffins.

olefins and

lower pro-

132 REFERENCE8

5

9 10

11 12 13 14 15 16 17 18 19 20 21 22 23 24

A. Mahay, F. Simard, G. Lemay, A. Adnot, S. Kaliaguine and 3. Monnier, Appl. C&al., 33 (1987) 55. A. May, G. Lemay, A. Adnot, I.M. Szoghy and S, Kaliaguine, J. Catal., 103 (1987) 480. H. Arai, A. Hironage and T. Seiyama, Proc. Pam-Pacific Synfuels Conf., Tokyo, November 17-19, 1982, pp. 137-144. F. Lefebvre, P. Gelin, C. Naccache and Y. Ben Taarit, in D. Olson and A. Int. Zeolite Conf., Rena, July 10-15, 1983, Bisio (Eds.), Proc. 6th Butterworths, Guildford, 1984, pp. 435-443. L. Tebassi, A. Sayari, A. Ghorbel, M. Dufaux, F. Ben Taarit and C. Naccache, in D. Olson and A. Bisio (Eds.), Proc. 6*h Int. ZeoIite Conf., Rena, July 10-15, 1983, Butterworths, Guildford, 1984, pp. 368-376. L. Tebassi, A. Sayari, A. Ghorbel, M. Dufaux and C. Naceache, J. Molec. Cat&., 25 (1984) 397-408. J.F. Garcia de .laBands, A. Corma and F.V. Melo, Appl. Catal., 26 (1986) 103-121. H, Arai and H, Tominaga, in T. Seiyama and K. Tanabe (E&r.), New Horizons in Catalysis, Prm. 7*b Int. Congr. Catal., Tokyo, June 30-July 4, 1980, Elsevier, Amsterdam, 1981, pp. 1446-1447. M. Goldwasser and C. Naccache, Proc. 9th Iberoamerican Symp. Catal., Lisbon, July 14-21, 1984, pp. 1398-1407. G. de1 Angel, B. Coq, R. Dutartre, F. Fajula, F. Figueras and C. Leclercq, in G.M. Pajonk, S.J. Teichner and J.E. Germain (Eds.), Spillover of adsorbed species, Elsevier, Amsterdam, 1983, pp. 301-308. D.R. Corbin, W.C. Seidel, L. Abrams, N. Herron, G.D. Stucky and C.A. Tolman, Inorganic Chemistry, Vol. 24, No. 12, 1985, pp. 1800-1803. L.B. Young, S.A. Butter and W.W. Kaeding, J. Catal., 76 (1982) 418. J. Nunan, J. Cronin and J. Cunningham, J. Catal., 87 (1984) 77. W.W. Kaeding and S.A. Butter, J., Catal., 61 (1980) 155. G.T.Kerr and A.W. Chester, Therm. Chim. Acta, 3 (1971) 113. M. Derewinski, J. Haber, J. Ptaszynski, V.P. Shiralkar and S. Dswigaj, Stud. Surf. Sci. Catal., 18 (1984) 209. J-C. Vedrine, A. Duroux, P. Dejaifve, V. Ducarne, H. Hoser and S. Zhou, J. Catal., 73 (1982) 147. A. Rahman, G. Lemay, A. Adnot and S. Kaliaguine, J. Cstal., 112 (1988) 453. Z. Gabelica, E.G. Derousne and N. Blom, Appl. Catal., 6 (1983) 22'7. A. Rahman, A. Adnot, G. Lemay and S. Kaliaguine, Appl. Catal., accepted. A. Mahay, Ph.D. Thesis, Universite lax&, Quebec City, Canada, 1986. K.H. Rhee, U.S. Rso, M. Stencel, G-A. Melson and J.E. Crawford, Zeolites 3 (1983) 337. 5. Kaliaguine, A. Adnot, G. Lemay and I,. Rodrigo, J. Catal., submitted for publication. F.P.J.M. iierkhofand J.A. Moulijn, J. Phys. Chem., 83 (19791 1612.