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Calcination of Pd(NH3)42+ and reduction to Pd° in NaX and CsX zeolites
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
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CALCINATION OF Pd(NH3)42+ AND REDUCTION TO Pd ~ IN NaX AND CsX ZEOLITES A. Sauvage, P. Massiani, M. Briend, D. Barthomeuf Laboratoire de R6activit6 de Surface, Universit6 Paris 6 (France) F. Bozon-Verduraz Laboratoire de Chimie des Mat6riaux Divis6s et Catalyse, Universit6 Paris 7 (France)
Summary The decomposition in 02 of Pd(NH3)42+ in NaX and CsX followed by TPO, UV-Visible and near IR occurs at lower temperature for PdCsX than for PdNaX. This is connected to different decomposition steps of Pd(NH3)x 2+. The reduction of Pd2+ to Pd ~ is easier in PdCsX than in PdNaX. Introduction The interaction of palladium tetrammine complexes with NaY has been extensively studied 1. It was observed in the case of Pt supported zeolites that the decomposition temperature of the ammine complex is different on PtNaX or PtCsX suggesting an influence of the framework chemical properties on the strength of interaction 2. The aim of the present work is to compare the decomposition of the Pd tetrammine complex and the reduction of Pd2+ on NaX and CsX to check the possible influence of the zeolite properties.
Experimental Pd7,4NaX and Pd8,oCs3oNaX (referred to as PdNaX and PdCsX) are prepared by exchange of the zeolite with a Pd(NH3)4CI2 solution at pH 10. The ion contents are expressed per unit cell. The decomposition, upon heating, of the complex is followed by TPO (thermoprogrammed oxidation) using thermal conductivity (TCD) or mass spectrometry (MS) and by UV-Visible and near infrared (NIR) spectroscopies. The reduction with H2 is studied by TPR (thermoprogrammed reduction) using TCD and by UV-Visible spectroscopy. The materials are heated at a rate of 7,5 K/rain in a flow of O2/He (oxidation) or H2/Ar (reduction). Results and Discussion Common features Figure 1 gives the TPO results (TCD analysis). For both samples a main peak is seen (585 K-PdCsX and 620 K-PdNaX). In addition smaller peaks are present at lower temperature, embedded in the big peak, or at higher temperature (around 610 K-PdCsX and 665 K-PdNaX). The detection of three peaks, comparable to the case of PdNaY, reveals the step-wise removal of NH3 from the supported complex 3. The decomposition of the desorbed phase followed by mass spectroscopy shows for both samples the removal at different temperatures of NH3 (505 K-PdCsX, 545 K-PdNaX) and of N2 (605 and 630 K-PdCsX, 630 and 680 K-PdNaX). As already observed for
130
PdNau 3, oxygen consumption mirrors N2 production. In addition our results show that NH3 is removed at temperature below the main TPO peaks of figure 1. A study using UV-Visible and near infrared spectroscopies shows that the ammine ligands are removed between 470 K and 700 K and replaced by framework oxygen as was reported for PdNaY 4. Simultaneously the NH3 peaks near 1525-1545 nm (NIR) decrease and disappear at about 650-680 K.
Comparison of PdNaX and PdCsX Figure 1, mass spectrometry, UV-Visible and NIR results show that the decomposition of the complex occurs a lower temperature in PdCsX than in PdNaX. The profile of temperature of decomposition steps are then not identical for the two zeolites. This probably arises from at least two parameters. At first the space available in the cavities is less in PdCsX than in PdNaX due to the cation size. This may modify the possibility of formation of specific Pd complexes like those proposed in PdNaY 4. Secondly the higher basic strength of framework oxygen in CsX compared to NaXS very likely influences the energy of Pd2+-Ozeo bonds. The reduction to Pd ~ is followed by TPR and UV-Visible spectroscopy. The maxima of the TPR peaks are near 395 K (PdCsX) and 435 K (PdNaX). The easier reduction of PdCsX is confirmed by UVVisible showing, for this sample,
an
A
J
Ta 450
550
650
Temperature(10
750
important disappearance of Pd 2+ ions Figure 1: TPO of PdNaX (a) and PdCsX (b) under an H2 flow at room temperature .. while PdNaX retains a large part of them. This behavior suggests the preferential location of Pd 2+ in the supercage for PdCsX and in the sodalite for PdNaX. In conclusion the zeolite characteristics influence both the decomposition of Pd(NH3)4 2+ and the further reduction of Pd 2+ to Pd metal. 1 W.M.H.Sachtler, Z. Zhang, Adv. Catal., 1993, 39, 129 2 A. de Mallmann, Thesis Paris 1989 A. de Mallmann, D. Barthomeuf,to be published 3 S.T. Homeyer, W.M.H. Sachtler, J. Catal., 1989, 117, 91 4 Z. Zhang, W.M.H. Sachtler, H. Chen, Zeolites, 1990, 10, 784 5 D. Barthomeuf, J. Phys. Chem., 1984, 88, 42
129
CALCINATION OF Pd(NH3)42+ AND REDUCTION TO Pd ~ IN NaX AND CsX ZEOLITES A. Sauvage, P. Massiani, M. Briend, D. Barthomeuf Laboratoire de R6activit6 de Surface, Universit6 Paris 6 (France) F. Bozon-Verduraz Laboratoire de Chimie des Mat6riaux Divis6s et Catalyse, Universit6 Paris 7 (France)
Summary The decomposition in 02 of Pd(NH3)42+ in NaX and CsX followed by TPO, UV-Visible and near IR occurs at lower temperature for PdCsX than for PdNaX. This is connected to different decomposition steps of Pd(NH3)x 2+. The reduction of Pd2+ to Pd ~ is easier in PdCsX than in PdNaX. Introduction The interaction of palladium tetrammine complexes with NaY has been extensively studied 1. It was observed in the case of Pt supported zeolites that the decomposition temperature of the ammine complex is different on PtNaX or PtCsX suggesting an influence of the framework chemical properties on the strength of interaction 2. The aim of the present work is to compare the decomposition of the Pd tetrammine complex and the reduction of Pd2+ on NaX and CsX to check the possible influence of the zeolite properties.
Experimental Pd7,4NaX and Pd8,oCs3oNaX (referred to as PdNaX and PdCsX) are prepared by exchange of the zeolite with a Pd(NH3)4CI2 solution at pH 10. The ion contents are expressed per unit cell. The decomposition, upon heating, of the complex is followed by TPO (thermoprogrammed oxidation) using thermal conductivity (TCD) or mass spectrometry (MS) and by UV-Visible and near infrared (NIR) spectroscopies. The reduction with H2 is studied by TPR (thermoprogrammed reduction) using TCD and by UV-Visible spectroscopy. The materials are heated at a rate of 7,5 K/rain in a flow of O2/He (oxidation) or H2/Ar (reduction). Results and Discussion Common features Figure 1 gives the TPO results (TCD analysis). For both samples a main peak is seen (585 K-PdCsX and 620 K-PdNaX). In addition smaller peaks are present at lower temperature, embedded in the big peak, or at higher temperature (around 610 K-PdCsX and 665 K-PdNaX). The detection of three peaks, comparable to the case of PdNaY, reveals the step-wise removal of NH3 from the supported complex 3. The decomposition of the desorbed phase followed by mass spectroscopy shows for both samples the removal at different temperatures of NH3 (505 K-PdCsX, 545 K-PdNaX) and of N2 (605 and 630 K-PdCsX, 630 and 680 K-PdNaX). As already observed for
130
PdNau 3, oxygen consumption mirrors N2 production. In addition our results show that NH3 is removed at temperature below the main TPO peaks of figure 1. A study using UV-Visible and near infrared spectroscopies shows that the ammine ligands are removed between 470 K and 700 K and replaced by framework oxygen as was reported for PdNaY 4. Simultaneously the NH3 peaks near 1525-1545 nm (NIR) decrease and disappear at about 650-680 K.
Comparison of PdNaX and PdCsX Figure 1, mass spectrometry, UV-Visible and NIR results show that the decomposition of the complex occurs a lower temperature in PdCsX than in PdNaX. The profile of temperature of decomposition steps are then not identical for the two zeolites. This probably arises from at least two parameters. At first the space available in the cavities is less in PdCsX than in PdNaX due to the cation size. This may modify the possibility of formation of specific Pd complexes like those proposed in PdNaY 4. Secondly the higher basic strength of framework oxygen in CsX compared to NaXS very likely influences the energy of Pd2+-Ozeo bonds. The reduction to Pd ~ is followed by TPR and UV-Visible spectroscopy. The maxima of the TPR peaks are near 395 K (PdCsX) and 435 K (PdNaX). The easier reduction of PdCsX is confirmed by UVVisible showing, for this sample,
an
A
J
Ta 450
550
650
Temperature(10
750
important disappearance of Pd 2+ ions Figure 1: TPO of PdNaX (a) and PdCsX (b) under an H2 flow at room temperature .. while PdNaX retains a large part of them. This behavior suggests the preferential location of Pd 2+ in the supercage for PdCsX and in the sodalite for PdNaX. In conclusion the zeolite characteristics influence both the decomposition of Pd(NH3)4 2+ and the further reduction of Pd 2+ to Pd metal. 1 W.M.H.Sachtler, Z. Zhang, Adv. Catal., 1993, 39, 129 2 A. de Mallmann, Thesis Paris 1989 A. de Mallmann, D. Barthomeuf,to be published 3 S.T. Homeyer, W.M.H. Sachtler, J. Catal., 1989, 117, 91 4 Z. Zhang, W.M.H. Sachtler, H. Chen, Zeolites, 1990, 10, 784 5 D. Barthomeuf, J. Phys. Chem., 1984, 88, 42