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Structure of FAU­type zeolites (USY).

úËõ May 2009 Vol.22 No.3  151(C) 2009 The Japanese Society for Synchrotron Radiation ResearchÔðZk·éû@ÆµÄCQuick_XAFSiQXAFSjÆGlM[ªU^ XAFSiDXAFSjª°çêéB±Ì¤¿ QXAFS @ÍCªõíðâ~¹¸ì®µ½óÔÅf[^ðA±µÄvª·éXL@ÅèC¿ÉæÁÄÍbÈº©çªöxÌZÔÅªè·é±ÆªÂ\ÅéBÜ½ QXAFS @Íù¶Ì XAFS uÌüÇÉæèÎ
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ªU Pd0 G}ðéØÉ{YJbvO½ÉKpµCFig. 2 Pd K­edge XAFS spectra for Pd/H_USY measured in an 8÷H2 ow at 300 K (rst cycle). Data were collected every 0.6min.

úËõðgÁ½À±Éæè¾çê½m©ÆCG}J­Ìè@ðZ·é±ÆÉæèC«íßÄ¢«ð¦·G}ª±¯Ä©o³ê½¤ðÐîµ½¢B

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gsbNX ¡ ª QXAFS @Éæé«pWEG}Ì`¬ßö¨æÑ®I®Ìð¾Fig. 3(a) Pd K­edge EXAFS Fourier transforms for Pd/H_USY
O(N) andmeasured in an 8÷ H2 ow, (b) CNs of Pd_nearest­neighboring Pd_Pd bonds determined by curve­t­ting analysis.

Fig. 4

Stepwise growth of Pd clusters through iterative exposure ofH2 and O2.

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ÅÍCñ20ªÅ Pd2{ ª Pd0 ÉÒ³³êÄ¢éÌÉÎµC2 ñÚÌf±üÈ~ÅÍCí¸©É¶¬µ½ Pd2{ ªñ2 ªÈàÅÒ³³êCPd0 ª¶¬µÄ¢½B1 ñÚÌf±üÉ¨¯é Pd2{ ÌÒ³¬xðÇÕµ½Æ±ëC1st runFig. 5

TEM pictures of Pd/USY exposed to H2. (a) 1st, (b) 4th.

É¨¯é Pd2{ ÌÒ³ßöÍ Pd2{ ZxÉÎµÄ 1 ÅisµC»Ì¬xèÍzÊiPd_Pdj©çß½ Pd0Ì¬·¬xÉÙÚµ©Á½Bµ½ªÁÄCPd2{ ÌÒ³(1)Ìæ¤ÉCNH3 ÌE£CH2 Éæé Pd2{ Ì Pd0 ÖÌÒÉæé Pd0 Ì¶¬Æ Pd0 NX^[`¬ª¯Éisµ³Ì 2 iKÅiÞÆl¦çêéBÄ¢éàÌÆl¦çêéBÜ½CPd2{ ÌÒ³¬xÍCfª³ÉÎµÄñ0.1ÅèCÙÆñÇfª³ÉÍË2{¨Pd0Pd(NH3)2{4 ¨Pd(1)¶µÈ¢±Æªª©Á½BPd(NH3 )2{4 ÌÒ³ßöÍC®

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Fig. 6(a) XANES of Pd/USY measured in the atmosphere of H2(1st). (b) Relative concentrations of Pd0 in Pd/H_USY plot­
ted as a function of time measured in an 8÷ H2 ow.
Fig. 7Pd2{ ÌÒ³¬xªfª³ÉË¶µÈ¢±Æ©çCPd NX^[Ì`¬ßöÉ¨¢ÄCNH3 ÌE£ª¥¬iKÅ(a) Pd K­edge EXAFS spectra for Pd/H_USY measured inan 8÷ H2 ow, (b) change in the coordination numbers ofthe nearest­neighboring Pd_Pd (b) measured in the temper­
ature programmed reduction.

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[nF°»¨ð¾é½ÅFig. 8In situ (a) ow­type, (b) bubbling­type cells for XAFS
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gsbNX ¡ ª QXAFS @Éæé«pWEG}Ì`¬ßö¨æÑ®I®Ìð¾Time­resolved QXAFS studies on the formation anddynamic behavior of the highly active Pd catalyst
Kazu OKUMURA

Tottori University, 4_101, Koyama­cho Minami, Tottori, 680_8552, Japan

Abstract The stepwise growth of Pd in a USY zeolite was followed by in situ scanning quick X­ray absorp­
tion ne structure (QXAFS) spectroscopy involving repeated alternating exposures to H2 and O2 ows atroom temperature. During the rst reduction of 0.4 wt÷_Pd/USY with 8÷ H2, Pd clusters of 13 atoms with acoordination number (CN) of 5.1 formed within 20 min in the supercage of USY. The growth followed rst­
order kinetics with respect to the concentration of Pd2{ and the CN of Pd_Pd. The clusters were stable up to443 K. The clusters were partially oxidized in less than 2 min on exposure to 8÷ O2, and then quickly reducedwith 8÷ H2 (second reduction) to aord larger Pd clusters of 26 atoms. The clusters continued to increase insize in a stepwise fashion on further alternate exposures to O2 and H2. The nely dispersed Pd0 species exhibit­
ed extremely high activity in the Suzuki­Miyaura coupling reactions when the o ­xylene solution was activatedwith H2­bubbling.

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