One-step synthesis of methyl isobutyl ketone from acetone and hydrogen over Pd/(Nb2O5/SiO2) catalysts

Applied Catalysis A: General 205 (2001) 61–69

One-step synthesis of methyl isobutyl ketone from acetone andhydrogen over Pd/(Nb2O5/SiO2) catalysts

Y.Z. Chena,∗, B.J. Liawb, H.R. Tana, K.L. Shena

a Department of Chemical Engineering, National Central University, Chung-Li 32045, Taiwan, ROCb Department of Chemical Engineering, Nanya Junior College, Chung-Li 32049, Taiwan, ROC

Received 11 January 2000; received in revised form 7 March 2000; accepted 8 March 2000

Abstract

The surface-phase oxides of niobia on silica substrate ((Nb2O5/SiO2), NS(x)) were prepared and characterized. Such oxideswere used as supports for palladium catalysts. The one-step synthesis of methyl isobutyl ketone (MIBK) from acetone andhydrogen in liquid phase was also investigated over Pd/NS(x) catalysts. Experimental results indicate that these catalysts wereeffective for the formation of MIBK; since little of the parallel by-product of isopropanol (IPA) was formed, these catalystsreached selectivities of 88–92% MIBK and 2–3% IPA at 30–35% conversion. The reactivity of Pd/NS(x) declined obviouslywith an increase of water content that accumulated in a semi-batch reaction system. The water could be partially expelledand the deactivation of catalysts could be improved by using a fixed bed continuous flow reaction system. © 2001 ElsevierScience B.V. All rights reserved.

Keywords:Methyl isobutyl ketone; Pd/(Nb2O5/SiO2) catalyst; Surface-phase oxide

1. Introduction

Methyl isobutyl ketone (MIBK) is an impor-tant product derived from acetone as it is a usefulsolvent for paints and protective coating systems.MIBK is commercially produced by a conventionalthree-step process (Scheme 1): (a) the equilibrium,base-catalyzed liquid phase aldol condensation ofacetone to form diacetone alcohol (DAA). Second,(b) an acid-catalyzed dehydration of DAA to mesityloxide (MO), and (c) a selective hydrogenation ofunsaturated ketone to MIBK with nickel or copperchromite catalyst.

These production processes are complicated andthe operational costs are high. The condensation equi-

∗ Corresponding author. Tel.:+886-3-4252-296;fax: +886-3-4252-296.

librium does not favor aldol formation, and the yieldsof the other two steps are relatively low. A corrosiveproblem also occurs due to liquid base and acid cata-lysts. Increasing attention has been paid to one-stepsynthesis of MIBK from acetone and hydrogen usinga catalyst with condensation, dehydration and hydro-genation functions. This multiple-functional catalystcan act by shifting the equilibrium in the conden-sation step in favor of MO by simultaneously andirreversibly hydrogenating it to MIKB.

Several catalytic systems have been reported forthe one-step synthesis of MIBK in a liquid phase atmoderate to high pressure (10–100 atm), in whichhigh selectivity to MIBK (>90%) was achieved. Thesehave included palladium supported on KOH–Al2O3 orMgO–SiO2 [1], CaO–MgO–SrO–Al2O3 [2], Nb2O5[3,4], zirconium phosphate [5], ZrO(OH)2-carbon[6], Ce, Hf and/or Ta oxides-carbon [7] and cation

0926-860X/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved.PII: S0926-860X(00)00545-7

62 Y.Z. Chen et al. / Applied Catalysis A: General 205 (2001) 61–69

Scheme 1. Conventional routes to MIBK.

exchange resins [1]. Recently, some catalytic systemsfor the one-step synthesis in the gas phase at atmo-spheric pressure have encompassed palladium sup-ported on SAPO-34 [8], SAPO-11 [9], KH-ZSM-5[10] or calcined Mg/Al hydrotalcite [11], nickel onMgO [12] or ALPON [13], platinum on H-ZSM-5[14] and HMFI [15], and copper supported on MgO[16]. The one-step process in the gas phase is simplerand more economical, but the selectivity of MIBK(60–80%) is much lower than that in the liquid phaseand the deactivation of catalysts remains a major limi-tation. Thus, finding a new or improved catalyst tooperate in the gas phase or liquid phase is a priorityconcern.

Niobia in its hydrated form is known as an activecatalyst for esterification, hydration, dehydration andaldol condensation [17]. The palladium catalyst sup-ported on niobia has a high activity and selectivityof MIBK in the liquid phase for the one-step process[18]. Although the bulk oxide of niobia does not havea large surface area nor good thermal stability, niobiacan be spread and deposited on SiO2 to form stablesurface-phase oxides [19,20]. Although one oxidedeposited onto another to form a surface-phase oxidemight lose its original bulk properties, Nb2O5 graftedonto SiO2 still possesses acidic sites for dehydration[21,22]. Therefore, the catalytic properties of niobiadeposited on SiO2 for condensation and one-stepsynthesis of MIBK are well worth exploring.

In this work we prepared and characterized thesurface-phase oxides of Nb2O5/SiO2 and the catalysts

of Pd/(Nb2O5/SiO2), as well as their catalytic pro-perties for the one-step synthesis of MIBK in theliquid phase. Experimental results indicate that thesurface-phase oxides of Nb2O5/SiO2 is as reactiveas Nb2O5 bulk oxide for condensation. Moreover,Pd/(Nb2O5/SiO2) systems are promising catalysts forthe one-step synthesis of MIBK from acetone andhydrogen in the liquid phase.

2. Experimental

2.1. Preparation

The surface-oxides of Nb2O5/SiO2 were preparedby incipiently impregnating silica with a hexanesolution of niobium(V) ethoxide. The impregnatedsamples were placed in a vacuum oven overnight toremove the solvent. Then the samples were decom-posed in a stream of nitrogen at 400◦C for 2 h and cal-cined in air at 500◦C for 2 h. The amount of niobiumethoxide required for the first monolayer of Nb2O5 onSiO2 was obtained from a stoichiometric calculationbased on the surface area of SiO2 and 16 Å2 occu-pied by each NbO2.5 unit [19]. The procedure wasrepeated to deposit a second and a third monolayerof Nb2O5. The resultant surface-phase niobia oxideswere designated as NS(1), NS(2) and NS(3) for one,two and three layers of niobia on silica and were usedas supports. The Pd/NS(x) catalysts were prepared byincipient impregnation of acidified aqueous solutionof PdCl2 (aqueous solution of Ni(NO3)2·6H2O), driedat 100◦C for 24 h and calcined in air at 400◦C for 4 h.

2.2. Characterization

The BET surface areas and pore size distributionsof NS(x) were obtained from an ASAP 2010 apparatusfrom nitrogen adsorption at−196◦C. X-ray diffraction(XRD) patterns were collected in a Siemens-500 X-rayphotometer operating at 40 kV and 30 mA and usingCu Ka radiation (λ=0.1542 nm).

The acid sites of catalysts were determined via aTPD-method that adsorbedn-butylamine. The cata-lysts were first pre-treated at 400◦C for 1 h under acarrier gas of helium, then cooled to room tempera-ture for adsorption ofn-butylamine for 0.5 h and then

Y.Z. Chen et al. / Applied Catalysis A: General 205 (2001) 61–69 63

flushed at 120◦C for 1 h. The adsorbedn-butylaminewas desorbed from 120 to 400◦C.

2.3. Reaction

The one-step synthesis of MIBK was conducted ina semi-batch reactor in which a fixed amount of ace-tone was loaded and hydrogen was continuously sup-plied to compensate for the consumed hydrogen tomaintain the total pressure at 20 atm and the tempera-ture at 160◦C. The life time test for catalysts was per-formed in a continuous fixed bed reactor equippedwith a back pressure regulator keeping the system ata total pressure of 20 atm. The reaction mixture wasanalyzed by a gas chromatograph with a 1/8 in.×6 ftCarbowax 20 M column attached to a flame ionizationdetector.

3. Results and discussion

3.1. Characterization of supports and catalysts

The surface-phase oxides of Nb2O5/SiO2 with vari-ous niobia loads were prepared and used as supports.Table 1 lists the BET surface areas, pore volumes andaverage pore sizes of these supports. The pore volumeper gram of SiO2 and average pore diameter slightlydeclined below the niobia loading of 27%. Althoughthe surface areas per gram of sample decreased withthe loading of niobia, the surface areas on a gramof SiO2 basis increased up to the loading of 40%.This increase demonstrated that the surface niobia washomogeneously distributed on the substrate of SiO2and that the pores of SiO2 were not obviously blocked.

Table 1Surface areas, pore volumes and average pore diameters of NS(x) supports

Support Nb2O5 loading (wt.%) Surface area Pore volume (cm3/gSiO2) Average pore diameter (nm)

m2/g m2/gSiO2

SiO2 0.0 274 272 1.58 17.5NS(0.5) 15.8 250 294 1.51 17.2NS(1) 27.4 226 311 1.38 16.8NS(2) 40.8 187 315 1.26 14.5NS(3) 48.6 142 277 1.04 13.1

Fig. 1. Pore size distribution of NS(1) and SiO2.

The pore size distribution of NS(1) nearly coincidedwith that of SiO2 substrate as presented in Fig. 1.

The distribution of the surface niobia on NS(1)was also examined by the energy dispersive analy-sis (Fig. 2). The elemental mapping is displayed inFig. 2(b and c), while the sample region is representedin Fig. 2(a). The good correlation between the ele-mental maps of Si and Nb also indicated an uniformdistribution of niobia on the substrate SiO2.

Fig. 3 demonstrates the X-ray diffraction results ofthe surface-phase niobia of NS(x) after calcination at600, 700 or 800◦C for 6 h. No Nb2O5 crystalline wasfound at 600◦C (Fig. 3(a)), as the diffraction peaks cor-responding to Nb2O5 crystalline evolved for NS(3) at700◦C (Fig. 3(b)), and for NS(2) and NS(3) at 800◦C(Fig. 3(c)). NS(1) exhibited better thermal stability


Fig. 2. X-ray energy dispersive analysis of NS(1). SEM micrograph of (a) the image region, (b) Si map and (c) Nb map.

than NS(2) and NS(3), because of the wetting of thefirst monolayer of surface niobia on silica through thebonding of Nb–O–Si [19,20].

The amounts of acid sites for NS(x) supports weredetermined by the adsorption ofn-butylamine and are

Fig. 3. XRD patterns of NS(1), NS(2) and NS(3). Pre-treated at(a) 600◦C, (b) 700◦C and (c) 800◦C.

listed in Table 2. The amount of acid sites per squaremeter increased with the loading of niobia (or the num-ber of layers deposited on SiO2). According to theseresults, the surface niobia above the first monolayerwas not homogeneously distributed layer by layer inatomic scale. Shirai et al. discovered that Nb2O5 de-posited on SiO2 possesses both Lewis and Brønstedacid sites [23] and their distributions depend on theloading and structure of the surface niobia.

3.2. Catalytic test

3.2.1. Effects of mass transferThe revolution rate of stirring for a gas–solid–liquid

reaction system is a critical factor for mass transfer.Table 3 summarizes the results of the one-step synthe-sis of MIBK over 0.3% Pd/NS(1) conducted at the re-volution rate between 200 and 800 rpm. Two acetones

Table 2Amount of acid sites on 0.1% Pd/NS(x) catalysts

Catalyst Acid amount

mmol/g cat. mmol/m2 cat.

0.1% Pd/SiO2 – –0.1% Pd/NS(0.5) 0.89 3.560.1% Pd/NS(1) 1.07 4.740.1% Pd/NS(2) 1.20 6.440.1% Pd/NS(3) 1.25 8.79


Table 3Effect of revolution rate on MIBK synthesis for 0.1% Pd/NS(1)catalysta

Conversion andselectivity

Revolution rate (rpm)

200 300 500 700 800

Conversion (%) 15.3 16.6 15.3 15.8 15.4

Selectivity (%)MIBK 93.0 93.0 92.2 92.2 92.6C5− 1.71 1.81 2.00 1.94 1.97IPA 0.80 0.76 1.09 1.14 0.80DAA 0.65 0.63 0.93 0.84 0.91MO 0.07 0.14 0.16 0.17 0.16MIBC 0.20 0.19 0.23 0.24 0.21DIBK 2.50 2.58 2.36 2.42 2.35TMB 0.92 0.90 0.87 0.88 0.88PHO 0.01 0.01 – 0.01 –ISOP 0.02 0.02 0.01 0.01 0.01Unknown 0.13 0.13 0.12 0.16 0.14C9+ 3.57 3.75 3.37 3.48 3.39

a Reaction conditions:T=160◦C, P=20 atm, acetone/0.1% Pd/NS(1)=50 g/0.4 g, reaction time=2 h and C9+=DIBK+TMB+PHO+ISOP+unknown.

were first condensated to DAA; then DAA was suc-cessively dehydrated to MO on the acid sites of NS(x);and finally MO was selectively hydrogenated to MIBKon the metal sites of palladium. Acetone might bedirectly hydrogenated to isopropyl alcohol (IPA), orMIBK and acetone might involve the same reactionseries as the formation of MIBK to form diisobutylketone (DIBK). Some compounds had a low mole-cular weight (<C5) from cracking on acid sites, whileothers (unknown) had a higher molecular weight fromsecondary condensation.

The conversions and selectivities are slightly af-fected by the revolution rate of stirring, as presented inTable 3. Apparently, this one-step synthesis of MIBKwas not limited by the mass transfer of hydrogen.Thus, the hydrogenation of mesityl oxide to MIBKwas not the controlling step of this one-step process.As compared with the reactivity of dehydration ofDAA on acid sites, the condensation of acetone wassupposed to be the controlling step in this one-stepsynthesis process of MIBK in the liquid phase. With arevolution rate of 300 rpm, the conversions of acetoneincreased linearly with the loading of catalyst in thereaction medium up to 0.4 g, as illustrated in Fig. 4.As the loading of catalyst increased beyond 0.4 g, thecondensation of acetone was more or less limited by

Fig. 4. Effect of 0.1% Pd/NS(1) catalyst loading on the conversionof acetone for one-step synthesis of MIBK.T=160◦C, P=20 atm,acetone=50 g and reaction time=2 h.

the transfer rate of acetone between the liquid andsolid phases. Moreover, the catalyst loading of 0.4 gand the revolution rate of 700 rpm were used for thefollowing catalytic tests in order to discriminate theeffect of mass transfer in this gas–solid–liquid system.

3.2.2. Compare NS(1) with other supportsSiO2, CHT (calcined Mg/Al hydrotalcite), Al2O3,

CaO-modified Al2O3, SiO2–Al2O3 and NS(1) were allused as supports for palladium catalysts with 0.3 wt.%loading for one-step MIBK synthesis. Table 4 summa-rizes the catalytic results for 2 h over these catalysts at160◦C and 20 atm. Pd/NS(1) with Lewis and Brønstedacid sites displayed the highest activity and the bestselectivity for the formation of MIBK of the catalyststested. However, Pd/SiO2–Al2O3 with Brønsted acidsites possessed a low activity. Pd/Al2O3 with Lewisacid sites and some base sites, and Pd/CaO–Al2O3and Pd/CHT with base sites, had considerable activi-ties and selectivities, but were less active than 0.3%Pd/NS(1).

Only the supports were used for the condensation ofacetone (Table 5) and the dehydration of diacetone al-cohol (Table 6) under the same reaction conditions asthe one-step synthesis of MIBK to understand the ef-fects of supports. The SiO2–Al2O3 support displayed


Table 4Effect of support on MIBK synthesis for 0.3% Pd/support catalystsa

Catalyst Acetone conversion (%) Selectivity (%)

MIBK IPA DAA MO DIBK

0.3% Pd/NS(1) 16.1 91.9 1.7 0.9 0.1 2.20.3% Pd/SiO2 0.6 4.4 – 92.0 2.9 –0.3% Pd/Al2O3 10.9 87.4 8.0 5.5 0.1 0.70.3% Pd/CaO–Al2O3 10.0 91.3 3.2 3.9 0.2 0.70.3% Pd/SiO2–Al2O3 4.2 88.5 0.1 8.5 1.2 0.10.3% Pd/CHT 9.4 91.9 0.1 5.7 1.0 0.7

a Reaction conditions:T=160◦C, P=20 atm, acetone/0.3% Pd/support=50 g/0.4 g and reaction time=2 h.

Table 5Condensation reaction of acetone on supportsa

Support Concentration (mol%)

Acetone DAA MO C9+

NS(1) 94.5 0.2 4.9 0.4NS(2) 94.5 0.2 5.0 0.4Al2O3 95.8 0.2 3.9 0.1SiO2–Al2O3 91.2 0.2 1.6 –CHT 95.4 0.2 3.7 0.7

a Reaction conditions:T=160◦C, P=20 atm, acetone/support=50 g/0.4 g, reaction time=2 h and C9+=DIBK+TMB+PHO+ISOP+unknown.

the lowest reactivity for condensation; this result iscoincident with the low activity for the formationof MIBK. Clearly, the Brønsted acid sites were notthe only sites needed for acetone condensation. Thesteps in Scheme 2 were proposed [24] for the con-densation reaction on acid catalysts. Lewis acid sitesare needed for the formation of enol from the rear-rangement of one molecule of acetone. Moreover, theintermediate of enol successively reacts with anotheracetone chemisorbed on Brønsted acid sites to formDAA or MO.

Scheme 2. Condensation reaction of acetone on acid catalysts.

Table 6Dehydration reaction of DAA on supportsa

Support Concentration (mol%)

Acetone DAA MO C9+

NS(1) 77.4 2.1 19.0 1.5NS(2) 76.3 2.3 20.2 1.2Al2O3 93.2 3.7 3.0 0.2SiO2–Al2O3 82.1 6.9 10.7 0.3CHT 97.7 1.4 0.9 –

a Reaction conditions:T=160◦C, P=20 atm, DAA/0.3% Pd/support=50 g/0.4 g, reaction time=2 h and C9+=DIBK+TMB+PHO+ISOP+unknown.

DAA was used to replace acetone as the reactantfor dehydration tests. Most diacetone alcohol wasreversed to form acetone and some diacetone alco-hol was dehydrated into mesityl oxide, as listed inTable 6. Although most DAA was reversed to acetone,NS(1) showed the highest reactivity for dehydratingDAA to MO. As compared with Al2O3, CaO–Al2O3and CHT, this high activity for dehydration mightaccount for why NS(1) assumes a good reactivity forthe formation of MIBK (Table 1).


Fig. 5. Conversions and selectivities during the time courses forone-step synthesis of MIBK.T=160◦C, P=20 atm and acetone/0.1% Pd/NS(1)=50 g/0.4 g.

3.2.3. Deactivation of Pd/NS(1) catalysts inliquid-phase process

Fig. 5 presents the conversions and selectivities forthe synthesis of MIBK during the time courses in asemi-batch system. The conversions did not increaselinearly as the reaction time continued beyond 4 h. Al-though deactivated during the courses of reaction, thecatalyst of Pd/NS(1) could be regenerated by flushingin a stream of hydrogen at the reaction temperature of160◦C. We speculated that the deactivation of the cata-lyst was attributed to the accumulated water from thedehydration of DAA. Various amounts of water intro-duced into the reaction system to confirm the effect ofwater verified that the conversion of acetone declinedsharply with the amount of water added (Fig. 6).

3.2.4. Effects of palladium and niobia loadingOnly a suitable number of metal sites on Pd/NS(1)

was needed, since the hydrogenation of mesityl oxidewas not the controlling step in the one-step process.The loading of Pd on Pd/NS(1) was reduced from 0.3to 0.03%; the results are summarized in Table 7. Theconversion of acetone and the selectivity of MIBKwere slightly affected down to the loading of 0.05%.At 0.03% loading the conversion of acetone and theformation of MIBK decreased markedly, a considera-ble amount of mesityl oxide was observed, and the

Fig. 6. Effect of water content on the conversion of acetonefor one-step synthesis of MIBK.T=160◦C, P=20 atm and ace-tone/0.1% Pd/NS(1)=50 g/0.4 g.

products of C9+ increased and IPA decreased. Thedensity of metal sites for the loading of 0.03% wastoo low to reduce MO to MIBK and facilitate theformation of C9+ from secondary condensation reac-tions on acid sites. The optimal loading of palladiumfor Pd/NS(1) catalyst ranged between 0.05 and 0.1%.

Table 8 summarizes the effects of niobia loadingfor 0.1% Pd/NS(x) catalysts, the reactivities based on

Table 7Effect of Pd loading on MIBK synthesis forx% Pd/NS(1) catalystsa


Pd loading (wt.%)

0.03 0.05 0.1 0.2 0.3

Conversion (%) 14.4 16.6 16.3 16.4 16.1

Selectivity (%)MIBK 74.5 92.2 92.4 92.4 91.9C5− 1.80 1.75 1.93 1.86 1.95IPA – – 0.76 1.27 1.74DAA 1.27 0.92 0.90 0.93 0.93MO 15.5 1.23 0.45 0.15 0.13MIBC – 0.15 0.14 0.16 0.15DIBK 2.12 2.33 2.33 2.23 2.23Unknown 3.87 0.59 0.16 0.13 0.12C9+ 6.92 3.68 3.82 3.47 3.40

a Reaction conditions:T=160◦C, P=20 atm, acetone/x% Pd/NS(1)=50 g/0.4 g, reaction time=2 h and C9+=DIBK+TMB+PHO+ISOP+unknown.


Table 8Effect of Nb2O5 loading on MIBK synthesis for 0.1% Pd/NS(x)catalystsa


Loading of Nb2O5

NS(0.5) NS(1) NS(2) NS(3)

Conversion (%) 16.4 16.9 17.4 17.7Reactivity (mmol/h m2 cat.) 70.9 80.6 99.9 133.3

Selectivity (%)MIBK 92.1 91.9 91.7 91.5IPA 0.41 0.75 1.03 0.88DAA 1.31 0.87 0.67 0.52MO 0.21 0.08 0.05 0.07C9+ 3.66 3.91 4.35 4.60

a Reaction conditions:T=160◦C, P=20 atm, acetone/0.1%Pd/NS(x)=50 g/0.4 g, reaction time=2 h and C9+=DIBK+TMB+PHO+ISOP+unknown.

a square meter of catalyst increased with the niobialoading and the formation of MIBK decreased andC9+ increased slightly. These results were coincidentwith the number of acid sites on NS(x) supports.The increase of acid sites facilitates the condensa-tion of acetone, which is the controlling step of thisone-step process, and also facilitates the secondarycondensation.

3.2.5. Effects of pre-reduction temperature ofcatalyst, and temperature and pressure for reaction

As the Group VIII metals supported on Nb2O5, theSMSI effect on the Pd/NS(1) catalyst reduced at ahigher temperature for the depression of hydrogen ad-sorption was found in our previous studies [25]. Ac-cording to our results [25], MIBK increased from 45 to75% and IPA decreased from 44 to 5% as the reductiontemperature of Pd/NS(1) rose from 300 to 400◦C forthe synthesis of MIBK in the gas-phase at atmospherepressure. However, this effect was not found in thiswork for the one-step synthesis in the liquid-phase, asillustrated in Table 9.

As the reaction temperature rose from 150 to 180◦C,the conversion obviously increased from 13 to 26%and the selectivity of MIBK reduced slightly from92 to 89%. This one-step synthesis process in theliquid-phase was not affected by the total pressure, asit was high enough (>20 atm) to maintain the reactionsystem in the liquid phase.

To expel the deactivated effect of accumulated wa-ter as described above, a fixed bed continuous flow

Table 9Effect of pre-reduction temperature on MIBK synthesis for 0.1%Pd/NS(1) catalystsa


Reduction temperature (◦C)

300 400 500

Conversion (%) 17.0 16.9 16.9

Selectivity (%)MIBK 91.5 91.8 90.3C5− 2.41 2.27 1.99IPA 0.54 0.75 2.53DAA 1.14 0.87 0.94MO 0.13 0.08 0.06MIBC 0.21 0.25 0.41DIBK 2.82 2.84 2.87C9+ 4.08 3.91 3.79

a Reaction conditions:T=160◦C, P=20 atm, acetone/0.1%Pd/NS(1)=50 g/0.4 g, reaction time=2 h and C9+=DIBK+TMB+PHO+ISOP+unknown.

reaction system was used for the life time testingfor 0.1% Pd/NS(1) catalyst at 150◦C, 20 atm, 5 h−1

WHSV and H2/acetone=0.2 (Fig. 7). The conversiononly declined from 28 to 25% and the selectivity wasmaintained around 90% for 177 h of time on stream.The 0.1% Pd/NS(1) catalyst was effective and stablefor the one-step synthesis of MIBK in the liquid phase.We believe that Pd/NS(x) catalysts are promising

Fig. 7. Life time test for 0.1% Pd/NS(1) catalyst for one-stepsynthesis of MIBK. T=150◦C, P=20 atm, WHSV=5 h−1 andH2/acetone=0.2.


alternatives to Pd/Nb2O5 in the one-step synthesisprocess.

4. Conclusions

The niobia can be spread homogeneously on silicato form the surface-phase oxide of Nb2O5/SiO2. Al-though the first deposited layer wetting on the SiO2substrate exhibited good thermal stability, the surfaceniobia sintered into crystallites at high temperatureabove the first layer. The surface niobia possessed aconsiderable amount of acid sites, which were effec-tive for condensation and dehydration. The amountof acid sites on NS(x) increased with the loading ofniobia on silica.

The surface-phase niobia could be used to re-place bulk niobia as supports for palladium catalystsPd/NS(x), which were effective for the one-step syn-thesis of MIBK in the liquid phase. The reactivities ofPd/NS(x) catalysts based on unit surface area were in-creased with the loading of niobia. The condensationof acetone was the controlling step in this one-stepsynthesis process; therefore, the mass transfer of hy-drogen between gas and liquid phase was not a criticallimitation for this gas–liquid–solid reaction system.The 0.05–0.1% loading was enough for the Pd/NS(x)catalysts for hydrogenation of MO to MIBK. Waterproduced from the dehydration of DAA accumulatedin a batch reaction system and evidently deactivatedthe Pd/NS(x) catalysts. Nevertheless the accumulatedwater could be expelled in a fixed bed continuousflow reaction system.

Acknowledgements

The authors would like to thank the ChinesePetroleum Corp. and the National Science Council of

the Republic of China for financially supporting thisresearch under Contract No. NSC88-CPC-E008-010.

References

[1] Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 13,Wiley, New York, 1979, p. 907.

[2] Y. Too, T. Nakayama, Japanese Patent 62,258,335 (10November 1987).

[3] T. Maki, T. Yokoyama, Y. Sumino, Japanese Patent 63,68,538(28 March 1988).

[4] Y. Higashio, T. Nakayama, Catal. Today 28 (1996) 127.[5] O. Onoue, Y. Mizutani, S. Akiyama, Y. Izumi, Y. Watanabe,

CHEMTEC January (1977) 36.[6] T. Maki, T. Yokoyama, Y. Sumino, Japanese Patent 63,96,147

(27 April 1988).[7] T. Maki, T. Yokoyama, Y. Sumino, Japanese Patent 63,96,146

(27 April 1988).[8] K.D. Olson, US Patent 4,704,478 (3 November 1987).[9] S.M. Yang, Y.M. Wu, Appl. Catal. A 192 (2000) 211.

[10] P.Y. Chen, S.J. Chu, C.C. Chen, N.S. Chang, W.C. Lin, T.K.Chuang, US Patent 5,059,724 (22 October 1991).

[11] Y.Z. Chen, C.M. Hwang, C.W. Liaw, Appl. Catal. A 169(1998) 207.

[12] L.M. Gandia, M. Montes, Appl. Catal. A 101 (1993) L1.[13] L.M. Gandia, R. Malm, R. Marchand, R. Conanec, Y. Laurent,

Appl. Catal. A 114 (1994) L1.[14] L. Melo, G. Giannetto, F. Alvarez, P. Magnoux, M. Guisnet,

Catal. Lett. 44 (1997) 201.[15] L. Melo, G. Giannetto, F. Alvarez, P. Magnoux, M. Guisnet,

J. Mol. Catal. A 124 (1997) 155.[16] V. Chikan, A. Molnar, K. Balazsik, J. Catal. 184 (1999) 134.[17] K. Tanabe, Catal. Today 9 (1990) 1.[18] Y. Higashio, T. Nakayama, Catal. Today 28 (1996) 127.[19] E.I. Ko, R. Bafrali, N.T. Nuhfer, N.J. Wagner, J. Catal. 95

(1985) 260.[20] J.G. Weissman, E.I. Ko, P. Wynblatt, J. Catal. 108 (1987) 383.[21] M. Nishimura, K. Asakura, Y. Iwasawa, J. Chem. Soc., Chem.

Commun. 22 (1986) 1660.[22] K. Asakura, Y. Iwasawa, Chem. Lett. 6 (1986) 859.[23] M. Shirai, N. Ichikuni, K. Asakura, Y. Iwasawa, Catal. Today

8 (1990) 57.[24] P.A. Burke, E.I. Ko, J. Catal. 129 (1991) 38.[25] H.R. Tan, M.S. thesis, National Central University, Taiwan,

1997.

Documents

One-step synthesis of methyl isobutyl ketone from acetone and hydrogen over Pd/(Nb2O5/SiO2) catalysts