- 學位論文
以氧化釔溶膠將銅鋅催化劑洗積在不鏽鋼基材上之研究
Washcoating Stainless Steel Substrate with Cu/Zn-Al Catalyst by Yttria Sol
摘要
本研究的目的在使用氧化釔溶膠(yttria sol, Nyacol)為黏著劑，將CuO/ZnO/Al2O3催化劑洗積於不鏽鋼微流道板(microchannel plate)上。再將洗積的微流道板組裝成微反應器(microreactor, MCR)，進行催化甲醇蒸氣重組(Steam reforming of methanol, SRM)反應，來生產富氫氣(hydrogen rich gas)，作為質子交換膜燃料電池(proton exchange membrane fuel cell)之燃料。 在實驗室，先將氧化釔溶膠與CuO/ZnO/Al2O3催化劑以及去離子水混合成觸媒漿料(catalyst slurry)，來進行塗佈。漿料的製作參數包含了固體含量(solid content, S)、溶膠含量(B content, B)以及攪拌時間(stir time, t)。以毛刷方式將混合的觸媒漿料洗積在具有微流道結構的不鏽鋼基材片上，製成催化試片。經乾燥(80 oC)，煅燒(350 oC)與稱重後，再將試片浸於水浴中，進行130 W、30 min的超音波振盪。藉由基材上觸媒洗積層在此 「標準振盪程序」處理時的重量損失率(FL)，來估計洗積層的附著性強弱。研究發現好的洗積參數，能控制FL於5 %以內。證實，商購的氧化釔溶膠為系統不錯的黏著劑。 MCR的SRM研究結果顯示，以氧化釔溶膠作為黏著劑製出的催化試片，在反應溫度為300 oC時，才能夠達到甲醇轉換率(CMeOH) 為98 %的目標。且觸媒漿料中B的含量，對催化效能會造成顯著的影響。B過高時，氧化釔的顆粒會過度的包覆在催化劑的銅表面上，使得催化劑的活性降低。研究發現， B/C比從0.05增加到0.1，CMeOH會從98 %降至65 %。 氧化釔溶膠雖然可以作為黏著劑來製作穩固的催化試片，但製出試片的催化活性仍不如預期。離子層析的分析結果得知，氧化釔溶膠中含有300 ppm的氯離子。通常，氯離子會降低金屬催化劑的活性，因此在研究室自行製作了不含氯離子的氧化釔溶膠，並用以製備觸媒漿料，發現自製的溶膠也可把CuO/ZnO/Al2O3牢固的洗積在不鏽鋼基材上(FL ~ 5 %)。固定床反應器的活性測試顯示，自製溶膠黏著的催化劑能將CMeoH = 98%所需的溫度大幅從300降低到210 oC。
並列摘要
In this study, a yttria sol is explored as a binder to coat powders of Cu/ZnO/Al2O3 catalyst onto of micro-channels engraved on stainless steel plates. The catalyst was prepared in the laboratory through the sequential precipitation method. Coated plates were then used for fabrication of microchannel reactor (MCR) to produce hydrogen. Steam reforming of methanol (SRM) was used as a model reaction for the production. A series of coating slurries were prepared by mixing the catalyst powders with the yttria sol. Prepared slurries were coated on the surface or the micro-channels of stainless steel substrates through the brushing method. Adhesion stability of coated layers on the substrates was estimated by fraction of weight loss (FL) during a standard ultrasonic impulsion (130 W for 30 min) in a D.I water bath. Three preparation parameters, i.e., solid content (S), binder content (B) and stirring time (t), have been found to affect the coating stability. A low FL of 5 % or less may be attained at S ~ 40%, B = 1.9 % and t = 12 h. The commercial sol of yttria has been demonstrated in this study as a good binder for the coating. The activity of yttria coated catalysts has been tested with the SRM reaction in MCR. Experimental conversion of methanol (CMeOH) was found to decrease with B/C ratio in the slurry. Evidently, the binder tends to block the diffusion of reactants to active sites of catalysts. SRM activity of yttria bound catalysts was also tested with Packed Bed Reactor(PBR). A reaction temperature of Tr = 300 oC was required from for a methanol conversion of CMeoH = 100%. Ion exchange chromatograph analysis further indicated that commercial Y2O3 sol contained 300 ppm Cl- counter ions. Cl- is generally detrimental to activity of metal catalysts. Chlorine-free Y2O3 sol was therefore prepared in the laboratory to bind our SRM catalysts in laboratory. Packed bed reactor test confirmed that the temperature required for CMeOH = 98% may be significantly decreased from 300 to 210 oC on using the Cl- free sol.