以皂土及二氧化鈦混合擔體製備顆粒及蜂巢式觸媒用於低溫SCR處理NOx之研究

Abstract

選擇性觸媒還原法(Selective catalytic reduction, SCR)廣泛用於商業上處理氮氧化物(Nitrogen oxides, NOx)。於SCR相關研究中，常以TiO2作為活性相觸媒之擔體，但其不具黏性需添加黏著劑方能鑄造蜂巢載體。故有學者將未改質皂土(Bentonite)作為黏著劑鑄造蜂巢載體或觸媒擔體所用，但其所製備之SCR觸媒脫硝效率不佳。因此本研究以共沉澱法將Mn-Fe作為活性相擔持於Bentonite-TiO2混合擔體，探討顆粒觸媒與蜂巢觸媒之NO轉換效率，找出最佳混合擔體(Bentonite:TiO2)比例，其需具備高脫硝效率、高蜂巢觸媒擔載量及可鑄造成一體成形蜂巢觸媒之特性。 所製備之觸媒於反應溫度150 °C下進行脫硝反應，比較本研究之Bentonite-TiO2顆粒觸媒與未改質Bentonite擔體觸媒SCR文獻，顯示本研究所使用之Bentonite-TiO2混合擔體及Bentonite單一擔體觸媒均有較高之NO轉換效率(> 90%)，並未因添加Bentonite而喪失TiO2之催化能力。另外，蜂巢式觸媒結果顯示，MnFe/TiO2¬觸媒黏度較低，且蜂巢觸媒之擔載量也最低；當Bentonite-TiO2混合擔體比例為1:1~1:3時，可提升蜂巢觸媒之擔載量，然而當混合擔體之Bentonite比例再持續提升時，其雖有較高之黏度，但蜂巢觸媒擔載量卻下降。另外，發現MnFe/Bentonite:TiO2=1:3觸媒在一次披覆時即可得到高披覆量及高脫硝效率。最後由一體成形蜂巢觸媒參數實驗得知，以50 wt%觸媒混合50 wt%水，可成功鑄造出一體成形蜂巢觸媒，而TiO2擔體混合Bentonite，可提升一體成形蜂巢觸媒鑄造之成功率。

Selective catalytic reduction of nitrogen oxides with NH3 is one of the most effective methods for removal of NOx from flue gases. In the SCR studies, TiO2 is developed as a superior support that exhibts high reactivity; however, it has no plasticity to extrude monolith applying on the field. Bentonite (clays) appears to have a relevant role as an inorganic binder and support. However, previous report showed that unmodified clays did not have great NO removal. Therefore, the aim of this research is to combine bentonite and TiO2 as bi-support, and then the catalysts were prepared by co-precipitation method. The NO conversion efficiencies of pellets and monolithic catalysts are discussed. To find out the best ratio of bi-supports, catalysts with high loading on the monolith and sucessful extruded monoliths were tested. The results show that bentonite-TiO2 catalysts had higher NO conversions than literature data which used unmodified Bentonite as support of SCR catalysts. The catalyst loading test on the monolithic showed that MnFe/TiO2 had low viscosity and less loading amount. However, bentonite:TiO2 ratios of 1:1, 1:2 and 1:3 have high viscosity and the highest loading amounts. In addition, MnFe/Bentonite:TiO¬2=1:3 could approach high NO conversion by only one time washcoat.