Catalytic performance and structural characterization of ferric oxide and its composite oxides supported gold catalysts for low-temperature CO oxidation

Abstract

The preparation and catalytic activity of ferric oxide and its composite oxides supported gold catalysts for low-temperature CO oxidation were investigated detailedly, and characterized extensively by XRD, XPS, TPR, EC and XAFS techniques. It was found that containing highly dispersed Au of partially oxidized state, these nano-structured oxides supported Au/Fe 2 O 3 and Au/NiFe 2 O 4 catalysts had higher low-temperature activities. The possible catalytic active center is the gold of partially oxidized state (Au ζ+ ). Owing to its chemical inertia and difficulty in dispersion on the supports, gold has long been regarded as a much less active catalyst than platinum group metals. However, recent studies [1][2][3] have clearly shown that gold is extraordinarily active for low-temperature CO oxidation. Supported gold catalysts, such as Au/TiO 2 , Au/MnO x , Au/ZnO, Au/Fe 2 O 3 , Au/Al 2 O 3 and Au/NiFe 2 O 4 , have been identified as promising catalysts used in chemical sensors [4][5][6] , sealed CO 2 lasers [7,8] and air purification devices [9,10] . Some of them are also employed for hydrogen elimination from CO 2 feed gas in urea synthesis [11,12] . These reaction data and applications indicate that Au and support interact synergistically, exhibiting high long-term CO oxidation activity near room temperature. The reason for the enhancement of the catalytic performance of these supported gold catalysts is thought to be related to the CO oxidation reaction mechanism and the structure of gold catalyst, such as gold particle size and chemical state. In order to clarify the mechanism of the catalytic oxidation of CO with O 2 , in situ IR, ESR and TPD-ITD techniques have been used, and some insight into the catalytic mechanism was obtained [13][14][15][16] . Furthermore, some supported gold catalysts such as Au/MnO x , Au/Fe 2 O 3 , Au/Al 2 O 3 , Au/Co 3 O 4 and Au/Mg(OH) 2 were examined using XPS, TEM, XAFS and Mössbauer surface characterization techniques [17][18][19][20][21][22][23] . Relatively little was understood about the possible catalytic active center [24]

The influence of gold on the optical properties of sol–gel derived titania

“…Experimental estimation of Au-O bonding distances from EXAFS data for Au-TiO 2 system [61] gave even shorter (Au-O) distances than theoretical predictions [26]. The Au-O bonding was also experimentally detected for other supported Au catalysts [62][63][64][65][66]. Based on this previous experience, it seems reasonable to assume that the formation of Au-O bonds can be exploited in order to tailor the band gap energy of TiO 2 .…”

Influence of pretreatment conditions on low-temperature CO oxidation over Au/MOx/Al2O3 catalysts

“…The results of XPS indicated that the most portion of gold species on the catalyst surface were metallic gold, with minor portion gold species might be in an oxidized state. Our previous studies [11] showed that the catalyst precipitation precursor was Au(OH) 3 , when it was treated in an oxygen atmosphere at a relatively low-temperature, gold retained certain oxidized state. The oxidized Au phase was reduced almost completely to metallic Au with the increasing calcinations temperature.…”

“…Gold catalysts on a single oxide support were extensively studied. Also, some composite oxide supports, such as ZnFe 2 O 4 , NiFe 2 O 4 , MgFe 2 O 4 [11] were investigated. Recently, the composite oxides supports of MO x /Al 2 O 3 were employed by Grisel and Nieuwenhuys to prepare the Au/MO x /Al 2 O 3 catalysts, and used for oxidation of CO and CH 4 [12] and CO selective oxidation in H 2 -rich gas [13].…”

Evaluation of carbon monoxide oxidation over CeO2/Co3O4 catalysts: Effect of ceria loading

“…Many catalysts have been designed and tested for CO oxidation under low temperature. For instance, noble metal catalysts, such as Au/Co 3 O 4 , Au/a-Fe 2 O 3 , Au/MnO x , Pt/SnO 2 , Pd/SnO 2 have been demonstrated to be very effective in CO oxidation [5][6][7].…”