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Silver Ions in Zeolite A are Reduced by H$_2$ only at High Temperatures when 8-Rings are Blocked by Cs$^+$. Crystal Structures of Dehydrated $Ag_9Cs_3$-A Treated with H$_2$ at 23, 310, and 470${^{circ}C}$
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  • Silver Ions in Zeolite A are Reduced by H$_2$ only at High Temperatures when 8-Rings are Blocked by Cs$^+$. Crystal Structures of Dehydrated $Ag_9Cs_3$-A Treated with H$_2$ at 23, 310, and 470${^{circ}C}$
저자명
KIm. Yang,Seff. Karl
간행물명
Bulletin of the Korean Chemical Society
권/호정보
1987년|8권 2호|pp.69-72 (4 pages)
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대한화학회
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이 논문은 한국과학기술정보연구원과 논문 연계를 통해 무료로 제공되는 원문입니다.
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기타언어초록

The structures of dehydrated $Ag_9Cs_3$-A treated with hydrogen gas at three different temperatures have been determined by single-crystal X-ray diffraction techniques. Their structures were solved and refined in the cubic space group Pm3m at 23(1) $^{circ}C$. All crystals were ion exchanged in flowing streams of aqueous $AgNO_3$/$CsNO_3$ with a mole ratio 1:3.0 to achieve the desired crystal composition. The structures treated with hydrogen at $23^{circ}C(a=12.288(1);{AA});and;310^{circ}C(a=12.291(2);{AA})$ refined to the final error indices R1 = 0.091 and R2 = 0.079, and 0.065 and 0.073, respectively, using the 216 and 227 reflections, respectively, for which I >3${sigma}$(I). In both of these structures, eight $Ag^+$ ions are found nearly at 6-ring centers, and three $Cs^+$ ions lie at the centers of the 8-rings at sites of $D_{4h}$ symmetry. One $Ag^{circ}atom$, presumably formed from the reduction of a $Ag^+$ ion by an oxide ion of a residual water molecule or of the zeolite framework during the dehydration process, is retained within the zeolite, perhaps in a cluster. In these two structures hydrogen gas could not enter the zeolite to reduce the $Ag^+$ ions because the large $Cs^+$ ions blocked all the 8-windows. However, hydrogen could slowly diffuse into the zeolite and was able to reach and to reduce about half of the $Ag^+$ ions in the structure only at high temperature ($470^{circ}C$). The silver atoms produced migrated out of the zeolite framework, and the protons generated led to substantial crystal damage.