The Effect of Zeolite Structure on Catalysis

Seff, Karl 전남대학교 촉매연구소 1996 촉매학술발표회 Vol.- No.13

Crystal Structure of Dehydrated Rb+ Exchanged Zeolite X, Rb17Na21Si100Al92O984

Kim, Yang,Seff, Karl,Kim, Duk-Soo,Lee, Seok Hee 濟州大學校 基礎科學硏究所 1998 基礎科學硏究 Vol.11 No.1

The crystal structure of dehydrated Rb+-exchanged zeolite X, stoichiometry Rb??Na??-X (Rb??Na??Si??Al??O??) pre unit cell, has been determined from single-crystal X-ray diffraction data gathered by counter methods. The structure was solved and refined in the cubic space group Fd??, a=25.007(3) Å at 21(1) ℃. The crystal was Prepared by ion exchange in a flowing stream using a 0.05 M aqueous RbOH solution(pH=12.7) The crystal was then dehydrated at 360 ℃ and 2×10 ?? torr for two days. The structure was refined to the final error indices, R??=0.047 and R??=0.040 with 239 reflections for which Ι>3σ(Ι). In this structure, 71 Rb+ ions per unit cell are found at six different crystallographic sites and 21 Na+ ions per unit cell are found at two different crystallographic sites. Four and a half Rb+ ions are located at site I, the center of the hexagonal prism. Nine Rb+ ions are found at site I' in the sodalite cavity (Rb-O=2.910(15) Å and O-Rb-O=78.1(4)˚). Eighteen Rb+ ions are found at site II in supercage (Rb-O=2.789(9) Å and O-Rb-O=92.1(4)˚). Two and half Rb+ ions, which lie at site II', are recessed ca. 2.07 Å into the sodalite cavity from their three O(2) oxygen planes (Rb-O=3.105(37) Å and O-Rb-O=80.6(5)˚). Thirty-two Rb+ ions are found at site III deep in the supercage (Rb-O=2.918(12) Å and O-Rb-O=71.9(4)˚), and five Rb+ ions are found at site III'. Seven Na+ ions also lie at site I. Fourteen Na+ ions are found at site II in the supercage (Na-O=2.350(19) Å and O-Na-O=117.5(6)˚).

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${^{\circ}C}$

KIm, Yang,Seff, Karl Korean Chemical Society 1987 Bulletin of the Korean Chemical Society Vol.8 No.2

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.

An X-ray Diffraction Study of Na, Ag-A Reduced by Hydrogen. Ag$_3\;^+$and Ag$_3\;^{2+}$ Clusters

Kim, Yang,Seff, Karl Korean Chemical Society 1984 Bulletin of the Korean Chemical Society Vol.5 No.4

The reduction of vacuum-dehydrated $Na_xAg_{12-x}-A, 0 {\le} x {\le} 9.2$, and its reoxidation by O$_2$, have been studied by X-ray powder diffraction. Also, the structure of $Na_6Na_6-A$ treated with hydrogen at room temperature has been studied by single crystal methods in the cubic space group Pm3m at $24{\circ}C (a = 12.221(2) {\AA})$. The diffraction pattern of dehydrated Ag$_{12}$-A reduced by H$_2$ contains only the (111) and (200) reflections of silver metal, indicationg that the zeolite structure has been lost, but the zeolite's diffraction pattern and structural integrity can be fully restored by oxidation with O$_2$ at 100 or 200${\circ}C$. In contrast, the structures of $Na_xAg_{12-x}-A$, x = 4.5 and 9.2, were not destroyed by treatment with hydrogen. Dehydrated Na$_6Ag_6$-A treated with 50 Torr of hydrogen gas at 24${\circ}C$ for 30 minutes has $6\; Na^+\;and\;1.27\;Ag^+$ ions at 6-ring sites. These $Ag^+ ions are associated with 2.54 Ag${\circ}$ atoms to form 1.27 $Ag_3^+$ clusters per unit cell. Also found were 0.7 $Ag_3^{2+}$ clusters per unit cell near the 8-rings. The structure was refined to the final error indices R$_1$ = 0.134 and R$_2$ (weighted) = 0.147, using 168 independent reflections for which $I_0 >3{\sigma}(I_0)$.

Structure of Ag^(3+)_(5) Cluster : Crystal Structure of Dehydrated Partially Ag+ Exchanged Zeolite A treated with Hydrogen at 350℃ 부분적으로 Ag+이온으로 치환한 제올라이트 A를 350℃에서 수소로 처리한 후 탈수한 구조

Kim, Yang,Karl Seff 부산대학교 1983 자연과학논문집 Vol.35 No.-

진공하에서 Na_(7·4)Ag_(4·6)-A를 탈수하고, 350℃에서 수소로 처리하고 난 후, 수소를 제거시킨 구조를 단결정 X선 회절법으로 Pm3m 공간군을 이용하여 결정하였다. (a=12.208 (2) Å) 이 구조는 I。>3σ(I。) 194개의 회절점을 사용하여 R_(1)=0.085, R_(2)=0.067을 얻었다. 결정구조 해석에 의하면, 두개의 다른 단위 세포로 나누어져 있었다. 40%의 단위세포로에는 8개의 Na^(+)이온이 6-링 평면 가까이 3회 회전축위에 위치하고 있고, 나머지 60%의 단위세포에는 7개의 Na^(+)이온과 한개의 Ag^(+)이온이 6-링 가까이 3회 회전축 상에 위치하고 있으며, 이 Ag^(+)이온은 다른 Ag물질과 결합하여 Ag^(0)-Ag^(+)=3.4Å이고, Ag^(0)-Ag^(0)=2.94Å이다. 모든 단위세포에는 0.65개의 Ag^(+)이온이 4-링 산소 이온과 결합하고 있다. The crystal structure of vacuum dehydrated Na_(7·4)Ag_(4·6)-A, treated with H_(2) at 350℃ and evacuated H_(2) at 350℃, has been determined by a single crystal X-ray diffraction method in cubic space group Pm3m at 24(1)℃; a=12.208(2)Å. The structure was refined to the final error indices R_(1)=0.085 and R_(2)(weighted)=0.067, using 194 independent reflections for which I。>3σ(I。). Crystallographic analysis shows that two types of unit cells can be distinguished. Approximately, in 40% of unit cell, eight Na^(+) ions are located on the threefold axis near 6-ring window. In the remaining 60% of unit cells, seven Na^(+) ions and one Ag^(+) are located on threefold axis nearly on 6-oxygen ring window. This Ag^(+) ion is associated with the other silver species and formed silver clusters Ag_(5)^(3+). This silver cluster is associated to 8-ring oxide ions and also to 6-ring oxide ions: Ag^(+)-Ag^(0)=3.4Å and Ag^(0)-Ag^(0)=2.94Å. 0.65 Ag^(+) ion is associated to 4-ring oxide ion and also to 6-ring oxide ion in all unit cell.

Crystal Structure of Dehydrated Cesium and Silver Exchanged Zeolite A,$ Cs_{7.3}Ag_{4.7}$-A

Yang Kim,Karl Seff Korean Chemical Society 1984 Bulletin of the Korean Chemical Society Vol.5 No.3

The structure of $CS_{7.3}Ag_{4.7}Si_{12}Al_{12}O_{48}$, vacuum dehydrated zeolite A with all Na+ ions replaced by $Cs^+$ and $Ag^+$ as indicated, has been determined by single-crystal x-ray diffraction techniques in the cubic space group, Pm3m (a = 12.282 (1) ${\AA}$). The structure was refined to the final error indices $R_1$ =\;0.089 and $R_2$ (weighted) = 0.099 using 347 independent reflections for whind intlch $I_0\;>\;3{\sigma}(I_0)$. Although deydration occurred at $360^{\circ}C$, no silver atoms or clusters have been observed. The 8-ring sites are occupied only by $Cs^+$ ion, and the 4-ring sites only by a single $Ag^+$ ion. The 6-ring sites contain $Ag^+$ and $Cs^+$ ions with $Ag^+$ nearly in 6-ring planes and $Cs^+$ well off them, one on the sodalite unit side. With regard to the 6-rings, the structure can be represented as a superposition of two types of unit cells: about 70 % have $4Ag^+$ and $4Cs^+$ ions, and the remaining 30 % have $3Ag^+$ and $5Cs^+$. In all unit cells, $3Cs^+$ ions lie at the centers of the 8-rings at sites of D4h symmetry; these ions are approximately 0.3 ${\AA}$ further from their nearest framework-oxygen neighbors than the sum of the appropriate ionic radii would indicate. To minimize electrostatic repulsions, the $Cs^+$ ions at Cs(1) are not likely to occupy adjacent 6-rings in the large cavity; they are likely to be tetrahedrally arranged when there are 4.

Crystal Structure of Hydrated Cesium and Silver Exchanged Zeolite A, Cs_(8.5) Ag_(3.5)-A

Kim, Yang,Karl Seff 부산대학교 1983 자연과학논문집 Vol.36 No.-

水和되어 있는 세슘 및 銀置換 제올라이트 A, Cs_(8.5) Ag_(3.5)-A의 結晶構造(a=12.311Å)를 單結晶 X-線回折法으로 決定하였다. 構造解析은 空間群 Pm3m을 使用하였다. Cs_(8.5) Ag_(3.5)-A 단결정을 AgNO_(3) 水溶液으로 먼저 Ag_(12)-A를 만든 후 HCN를 吸收시킨 CsOH 溶液으로 flow method에 의하여 만들었다. 水和된 Cs_(8.5) Ag_(3.5)-A 構造에서는 3개의 Cs^(+)이온이 8-ring의 中心에 D_(4h) 대칭위치에 위치하고 있었다. 또 다른 3個의 Cs^(+)이온을 4-ring 반대편에 위치하고 있었고 나머지 2.5개의 Cs^(+)이온은 3回 回轉軸上의 큰 空洞 깊숙이 位置하고 있었다. 1개의 Ag^(+)이온은 소다라이트 케이지 깊숙이 位置하고 있었다. 1.5개의 Ag^(+)이온은 O(3) 산소이온으로 된 (111)평면에서 0.37Å 소다라이트케이지 쪽으로 나머지 1개 Ag^(+)이온은 큰 洞空 쪽으로 0.78Å 移動한 위치에 있었으며 이들 3.5개의 Ag^(+)이온을 모두 3回 回轉軸上에 位置하고 있어서 O(3) 산소이온과 結合하고 있었다. 이 구조는 I>3σ(I)가 되는 239回折點을 써서 R_(1)=14%를 얻었다. The crystal structure of hydrated cesium and silver exchanged zeolite A, Cs_(8.5) Ag_(3.5)-A has been determined by a single crystal X-ray diffraction the method in cubic space group Pm3m at 24(1)℃;a=12.311Å. The structure was refined to the final error indices R_(1)=0.140 using 239 independent reflections for which I>3σ(I). Crystallographic analysis shows that three Cs^(+) ions are located at the center of 8-oxygen rings, and three Cs^(+) ions in the large cavity opposite 4-rings. 2.5 Cs^(+) ions are on the threefold axes and are associated with 6-ring oxygen. These ions recessed deep into the large cavity, 2.13Å from the (111)plane at 0(3). 3.5 Ag^(+) ions are located at the three different crystallographic sitis on the threefold axes. All the Ag^(+) ions are associated with 6-ring oxygens.

Silver Ions in Zeolite A Are Reduced H₂Only at High Temperatures When 8-Rings Are Blocked by Cesium Ions

Kim, Yang,Karl Seff 부산대학교 기초과학연구소 1988 부산대학교 기초과학연구소 연구논문집 Vol.8 No.-

The structures of dehydrated Ag_(9)Cs₃-zeolite A treated with hydrogen gas at three different temperatures have been determined by single-crystal X-ray diffraction techniques. Their strutures were solved and refined in the cubic space group pm3m at 23(1)℃. All crystals were ion exchanged in flowing streams of aqueous AgNO₃/CsNO₃with a mole ratio of 1:3.0 to achieve the desired crystal composition. The structures treated with hydrogen at 23℃(a=12.288(1)Å) and 310℃ (a=12.291 (2)Å)refined to the final error indices R₁=0.091, R₂=0.079 with 216 reflections. and 0.065, 0.073 with 227 reflections,respectively, for which I>3σ(I). In both of these structures,per unit cell, eitht Ag+ions are found nearly at 6-ring centers and three Cs+ions lie at the centers of the 8-rings. One Ag^(0)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 bloked all 8-rings. However, at 470℃ and 200 Torr,hydrogen could diffuse slowly into the zeolite and was able, in about 10 min, to reach and to reduce about half of the Ag+ions in the single crystal. The silver atoms produced migrated out of the zeolite framework, and the protons generated led to substantial crystal damage.

X-ray diffraction study of Ag_(+), Ag_(0), and Ag clusters in Zeolite A

Kim, Yang,Karl Seff 부산대학교 1983 자연과학논문집 Vol.35 No.-

전공하에서 Na_(x)Ag_(12-x)-A(0≤x≤9.2)를 탈수시키고, H_(2)로 환원시키고, O_(2)로 산화시킨 제올라이트를 X선 분말법으로 연구하였다. 실온에서 H_(2)로 처리한 Ag_(6)Na_(6)-A의 구조는 Pm3m의 공간군을 써서 X-선 단결정법으로 해석하였다. 탈수된 Ag_(12)-A는 수소 기류하 15분간 처리하니 은의(111), (200)회절점 이외는 회절 패턴을 관찰할 수 없었으나, 이 수소로 처리한 Ag-A를 100℃ 및 200℃에서 각각 산소를 통과 시키니, 제올라이트 분말은 좋은 X-선 회절 패턴을 주므로, 제올라이트의 구조가 산소처리로 회복됨을 나타내었다. 따라서, 수소 처리로 제올라이트의 구조가 완전히 파괴되는 것은 아니다. 탈수한 Ag_(6)Na_(6)-A를 50 torr의 수소기체로 처리하고 구조를 결정한 결과, 6개의 Na^(+)이온은 6-링 가까이, 3회 회전축 상에 놓여있고, 이 이온은 O(3)의 (111)평면으로부터 0.19Å 큰 공동쪽으로 물러나와 위치하고 있었다. 1.27 Ag^(+) 이온은 6-링의 다른 3회 회전축 상에 놓여 있었고, O(3) 평면에서 0.98Å 큰 공동쪽으로 나와서 위치했다. 이들 Ag^(+) 이온은 2.54개의 Ag^(0) 원자와 결합하여, 단위세포당 1.27개의 Ag_(3)^(+) 은의 크리스터를 이루고 있었다. 또 단위 세포당 0.7개의 Ag_(3)^(2+) 은의 크리스터는 8링 가까이에 위치하고 있었다. 이 구조는 I。>3σ(I。)인 168개의 회절점은 쓰서 R_(1)=0.134이었다. The vacuum dehydrated Na_(x)Ag_(12-x)-A(0≤x≤9.2), reduced by H_(2) and then oxidized by O_(2), have been studied by x-ray powder diffraction method. The crystal structure of Ag_(6)Na_(6)-A treated with hydrogen at room temperature has been also studied by a single crystal x-ray diffraction method in cubic space group Pm3m at 24℃. a=12.221.(2)Å. The dehydrated Ag_(12)-A, treated by flowing hydrogen gas for 15 minutes, gave almost no diffraction pattern except (111) and (200) reflections of silver metal. However, after the hydrogenated Ag_(12)-A was treated by flowing oxygen at 100℃ and 200℃, respectively, for 15 minutes, these zeolite powder samples gave good x-ray diffraction patterns. Therefore, the zeolite structures were restored. For Na_(x)Ag_(12-x)-A (x=4.5 and x=9.2, respectively), the structures of zeolite were not destroyed upon hydrogen treatment. The structure of dehydrated Ag_(6)Na_(6)-A treated with 50 Torr of hydrogen gas has the following unit cell composition; 6 Na^(+) ions located on the threefold axes of 6-rings and recessed into the large cavity by 0.19Å from (111) plane at O(3). 1.27 Ag+ ions were located at another crystallographically different threefold axes of 6-rings and recessed into large cavity by 0.98Å from (111) plane of O(3). These Ag^(+) ions were associated with 2.54 Ag^(0) atom and formed 1.27 Ag_(3)^(+) cluster per unit cell. 0.7 Ag_(3)^(2+) cluster was also found per unit cell nearby the 8-oxygen rings. The structure was refined to the final error indices, R_(1)=0.134 and R_(2) (weighted)=0.147, using 168 independent reflections for which I。>3σ(I。).

Crystal Structure of Dehydrated Partially Ag$^+$-Exchanged Zeolite A, Ag$_{4.6}Na_{7.4}$-A, Treated with Hydrogen at 350${^{\circ}C}$

김양,Kim Yang,Seff Karl Korean Chemical Society 1985 Bulletin of the Korean Chemical Society Vol.6 No.4

The crystal structure of The crystal structure of $Ag^+$-Exchanged Zeolite A, $Ag_{4.6}Na_{7.4}-A$, dehydrated, treated with $H_2$, and evacuated, all at $350^{\circ}C$, has been determined by single crystal x-ray diffraction methods in the cubic space group Pm3m at $24(1)^{\circ}C;$ a = $12.208(2)\AA.$ The structure was refined to the final error indices R1 = 0.088 and R2 (weighted) = 0.069 using 194 independent reflections for which II_0$ > $3{\sigma}(I_0)$. On threefold axes near the centers of 6-oxygen rings, $7.4 Na^+$ ions and $0.6 Ag^+$ ions are found. Two non-equivalent 8-ring $Ag^+$ ions are found off the 8-ring planes, each containing about $0.6 Ag^+$ ions. Three non-equivalent Ag atom positions are found in the large cavity, each containing about 0.6 Ag atoms. This crystallographic analysis may be interpreted to indicate that $0.6 (Ag_6)^{3+}$ clusters are present in each large cavity. This cluster may be viewed as a nearly linear trisilver molecule $(Ag_3)^0$ (bond lengths, 2.92 and 2.94 $\AA;$ angle, $153^{\circ})$ stabilized by the coordination of each atom to a Ag^+$ ion at 3.30, 3.33, and 3.43 $\AA$, respectively. In addition, one of the silver atoms approaches all of the 0(1) oxygens of a 4-ring at $2.76\AA.$ Altogether $7.4 Na^+$ ions, $1.8 Ag^+$ ions, and 1.8 Ag atoms are located per unit cell. The remaining $1.0 Ag^+$ ion has been reduced and has migrated out of the zeolite framework to form silver crystallites on the surface of the zeolite single crystal.