| Summary: | 博士 === 國立清華大學 === 化學系 === 86 === Beta沸石具有較大的孔洞及適中的酸性，故可廣泛的被應用於很多石
化工業上。直接以水熱法製得的高矽鋁比之Beta沸石，結晶性與結晶產率
均不佳。一般可試以脫鋁的方法，由低矽鋁比的樣品為起始物來製作。本
研究旨在探討以不同脫鋁方法，包括酸萃取與Si取代等法，試由較低矽鋁
比之Beta沸石製得較高矽鋁比者；尋求較適宜的脫鋁條件。再由beta沸石
承載Pt後之TPR圖譜，了解脫鋁過程中缺陷位置之生成與消失。此TPR技術
亦被用來探討Pt在Beta沸石中可能存在的物種與其分佈。 酸萃取法主
要是將沸石置於不同濃度的無機酸水溶液中攪拌三天後，經過濾，水洗，
乾燥與焙燒的步驟而得。經酸萃取法處理後，PQ公司生產之beta沸石的矽
鋁比值可從11提高至150 以上，並導致沸石酸量減少，強酸座之比例則相
對提高。XRD 測試結果顯示，以高至6 M 之硝酸或鹽酸處理，脫鋁後Beta
沸石仍能保有其結晶結構，但熱穩定性並不因矽鋁比值之提高而增加。此
是因脫鋁後缺陷位置增多之故。溫度對酸處理之效果的影響不甚明顯。脫
鋁的程序探討，由酸處理後之樣品中有水合鋁離子與Al(H2O)4(SO4)+之物
種存在，可說明其乃經鋁之萃取與水合之步驟。該水合鋁離子可被NaNO3
交換出來，顯示其可取代沸石晶格之陽離子，而有平衡沸石結構電荷之作
用。 矽取代法是以(NH4)2SiF6水溶液為矽源，在80℃下處理Beta沸石
，以進行脫鋁和植矽的反應。此法的脫鋁效果受矽溶液之濃度的影響頗甚
。當每克Beta沸石中SiO2添加量高於2.25 mmole時，由XRD可知沸石的結
晶結構已受破壞。此是因反應過程中有強酸性的HF生成之故。利用此法將
矽植入1 M HNO3處理後之Beta沸石中，矽鋁比可由90提高到127。由NMR光
譜可知，在植矽的過程中水合鋁離子會被交換出來，加入之矽則會植入因
脫鋁而產生的缺陷位置中。由於矽的填補，植矽前後樣品的結晶度並無明
顯的差異。 白金離子以初濕含浸或離子交換法添加於Beta沸石後，由
TPR (程溫還原， Temperature-Programmed Reduction)的測試結果可知
，其可能存在的物種及其還原溫度分別為：PteO及PteO2 (沸石孔洞外表
面之白金氧化物，Tr分別為-50 ℃與20 ℃)，PtoO及PtoO2 (孔洞內白金
氧化物，Tr 分別於80 ~ 110 ℃與130 ℃)，平衡晶格電位之Pt4+離子(
Pt4+ coordinated to Al-OH，Tr = 250 ℃)與Pt-(-O-Si≡)yn-y物種
(和Si-OH鍵結之白金物種，n = 2或4，y = 1 ~ 4，Tr = 400 ~ 550 ℃)
等。在不同脫鋁程度之beta沸石承載白金的樣品中，由Pt-(-O-Si≡)yn-y
物種的存在與否，可知脫鋁後沸石結構上的變化。即沸石經酸處理後，結
構上產生許多具有SiOH基團的缺陷位置，而使添加的白金可嵌入其中，產
生Pt-(O-Si≡)yn-y (n = 2或4，y = 1 ~ 4)之物種。植矽後，則因植入
之矽補到該hydroxyl nest中，所添加的白金則無法進入此種結構。故於
TPR圖譜中看不到Pt-(O-Si≡)yn-y物種被還原的訊號。 由TPR探討製
備條件對Beta沸石上之白金物種及其還原特性的影響則發現，(1)不同白
金前驅物由於在水中解離出之白金錯離子的電性不同，其進入沸石孔道之
難易程度依序為: PtCl4 > Pt(NH3)4(NO3)2 > H2Pt(OH)6。(2)一般
而言，白金錯離子較偏好留在沸石之外表面。但提高白金溶液濃度，可使
白金錯離子較易進入沸石孔道中。此錯離子一旦進入Beta沸石孔道後，會
先和≡Si-OH基團作用，其餘則留在孔道中，再經焙燒後便會形成PtoOx
。(3)沸石之陽離子形式不同，對白金物種的還原溫度亦有所影響。陽離
子為H+形式時，因有穩定白金粒子的功能，需較高溫度才能使白金物種還
原。再氧化效果亦受沸石陽離子不同而異。對Na+形式者而言，在再氧化
的過程中，白金物種幾乎不再回到沸石孔道中。而在H+形式之沸石中，則
當再氧化溫度為400 ℃時，即可使部分白金物種回到孔道中，而得和新鮮
樣品相近的結構。當再氧化溫度為500 ℃時，不論陽離子為何種形式均可
見有脫氧的現象。
Beta zeolite has been widely used in many petrochemical
industries due to its high Si/Al ratio, 12-ring pore opening and
moderate acidity. There is an optimum range in Si/Al for getting
Beta zeolite with good crystillinity and high crystal yield by
directly hydrothermal synthesis. The alternative method for
highly siliceous zeolite Beta is post synthesis. In this work,
we studied dealuminations of the Beta zeolite with acid leaching
and Si-replacing.Prepared samples were characterized by ICP/AES,
MAS NMR, NH3-TPD, XRD, etc. to realize the variation in
composition, acidity and thermal stability. Platinum were then
added to the parent and dealuminated Beta zeolites. TPR
(temperature-pregrammed reduction) technique was used to study
the reduction properties of all Pt/Beta zeolite samples.
Acid-leached Beta zeolite were prepared by suspending zeolite
powders in inorganic acid (such as nitric acid, hydrochloric
acid and sulfuric acid) solutions and stirred at room
temperature for three days. Suspended solutions were
subsequently filtrated, washed, dried in 100 ℃ and calcined up
to 540 ℃. The Si/Al of Beta zeolite can increase from 11 to
higher than 150 after leached with 4 M HNO3 solution. The acid
amount and the weak acid sites decreased as Al content on
framework decreased. The thermal stability of Beta zeolite
become poor after dealumination due to a formation of defect
sites. The Al(H2O)63+ species are found occluded in zeolite
cavity and act as cations in acid-leached zeolites. Si-
replacement of Beta zeolite was performed by stirring a
suspension of Beta in (NH4)2SiF6 solution at 80 ℃. The
concentration of (NH4)2SiF6 solution significantly affected the
resulted Si/Al ratio. The zeolite structure damaged severely as
the Si amount added was higher than 2.25 mmole per gram Beta
zeolite due to a formation of HF during Si-treatment. Si/Al
ratio of acid-leached Beta zeolite can be increased from 90 to
127 by further Si-replacement. In this treatment, the Al(H2O)63+
ions were exchanged byNH4+ ions. And the Si added would insert
into the hydroxyl nest of dealuminated Beta zeolite. It
maintained the crystillinity of dealuminated Beta zeolite due to
Si insertion. Platinum ions were dispersed onto the starting
and the treated samples through impregnation and/or ion-exchange
of aqueous Pt(NH3)4(NO3)2. Chemical environments of dispersed
platinum were characterized by TPR technique. Five major
signals, in reduction temperature (Tr) regions around -50, 20,
80, 130 and 480 ℃ were distinguished from these TPR traces and
characterized as reductions of platinum oxides dispersed on the
external surface of zeolite, PteO (Tr = -50 ℃) and PteO2 (Tr =
20 ℃), platinum oxides occluded in channels (PtoO and PtoO2, Tr
= 80 and 130 ℃, respectively), and Pt-(-O-Si()yn-y (Tr around
480 ℃, n = 2 or 4, y = 1 ~ 4) complexes coordinated to external
surface or defects of zeolite. From the variation in the
contribution of the 480 ℃ peak in TPR traces, a formation of
Si-OH silanol function groups on the zeolite surface during the
dealumination treatment and an elimination of these groups
during the silicon-insertion treatment are indicated. The
distribution of platinum was found to vary with the cation form
(H+ or Na+) of Beta zeolite, and the type and the concentration
of platinum precursor used in the preparation stage. The Pt(
OH)62- anion tended to deposit on the external surface of
zeolite, while cations of PtCl4-x(H2O)xx+ and Pt(NH3)42+
preferred to be occluded into zeolite channels and coordinated
to silanol groups on zeolite defects. When the concentration of
platinum solution was high, Pt(NH3)42+ ions also tended to be
occluded into zeolite channels. The occluded and coordinated Pt
sintered onto the external surface upon reduction. Upon a
reoxidation treatment at 400 ℃, the sintered platinum stayed on
the external surface if the zeolite is in the Na-form, but might
redisperse back into zeolite channels in the H-form zeolite.
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