Ga ion-doped ZrO2 Catalyst Characterized by XRD, XAFS, and 2-Butanol Decomposition

Takashi Yamamoto, Akihito Kurimoto
2019 Analytical Sciences  
Group 2, 3, and 13 element-doped zirconium oxide catalysts M-ZrO 2 (M = Mg, Sr, Y, La, Ce, Sm, Er, Yb, B, Al, Ga, In, and Tl. 5 mol%) were prepared by impregnation of each metal salt aqueous solution on amorphous zirconium hydroxide, followed by calcination at 773 K. The M-ZrO 2 samples were characterized by the catalytic performance of 2-butanol decomposition at 573 K, XRD, XANES and EXAFS spectroscopic techniques. Detailed analyses were performed herein for a series of Ga-ZrO 2 with various
more » ... rO 2 with various doping amounts in the range of 1-60 mol%. The addition of Group 2 and 3 elements little influenced the catalytic performance of ZrO 2 itself to promote dehydration to produce 1-butene with 90% selectivity. Ga-ZrO 2 and In-ZrO 2 gave methyl ethyl ketone as the main product via dehydrogenation. The doped Ga ion mainly existed inside the bulk of zirconia by forming the Ga x Zr 1−x O 2 solid solution up to 5 mol%. Highly doped species more than 10 mol% aggregated to form -Ga 2 O 3 . Each fraction forming the solid solution and Ga 2 O 3 -like species was evaluated by XANES analysis. performance of ZrO 2 . In the present study, we prepared Group 2, 3, and 13 element-doped ZrO 2 prepared by impregnation of metal salt onto amorphous zirconium hydroxide, followed by calcination. The surface properties were examined using 2-butanol conversion as a model catalytic reaction. The textural and local structures were also investigated by X-ray diffraction (XRD) and XAFS. Experimental Zr(OH) x was obtained by hydrolysis of ZrOCl 2 ·8H 2 O (Nacalai Tesque, GR) with 25 mass% NH 3 aqueous solution at room temperature 16, 20 . The final pH value was adjusted to 10, and the aging time was 12 h. The obtained gel was repeatedly washed with distilled water until free of Cl − by the AgNO 3 test, then dried at 383 K for 12 h. Metal-ion-doped zirconium oxides were prepared by impregnation of Zr(OH) x with an aqueous solution of metal salt at 353 K, followed by calcination at 773 K for 3 h in air. As for the metal salt, H 3 BO 3 , Al(NO 3 ) 3 ·9H 2 O, Y(NO 3 ) 3 ·nH 2 O, In(NO 3 ) 3 ·3H 2 O, Ce(NO 3 ) 3 ·6H 2 O, Sm(NO 3 ) 3 ·nH 2 O, Yb(NO 3 ) 3 ·nH 2 O, TlNO 3 (Wako Pure Chemical), Mg(NO 3 ) 2 ·6H 2 O, La(NO 3 ) 3 ·6H 2 O (Nacalai), Ga(NO 3 ) 3 ·nH 2 O (Kojundo Chemical Laboratory), Sr(NO 3 ) 2 (Kishida Chemical), and Er(NO 3 ) 3 ·nH 2 O (Rare Metallic) were utilized. The prepared catalyst is denoted as M-ZrO 2 or xMZ, where x and M refer to the molar fraction of a metal atom to zirconium and a kind of doped element, respectively. Except for Ga, the amounts of doped element were 5 mol% based on a monomer molecule. Gallium oxide and oxyhydride polymorphs were prepared with reference to a previous publication 22, 23 . -GaO(OH) was obtained by the hydrolysis of the gallium nitrate aqueous solution with the NH 3 aqueous solution at pH 9 and filtration, followed by drying at 383 K for 12 h. -Ga 2 O 3 was obtained by calcination of -GaO(OH) at 773 K for 3 h in air. The and -Ga 2 O 3 were obtained by calcination of gallium nitrate in air for 3 h at 1073 and 773 K in air, respectively. The XRD patterns were recorded with a Miniflex diffractometer (Rigaku) equipped with a Ni-filtered Cu K radiation source. The Ga K-edge X-ray absorption spectra were recorded with a Looper (Rigaku) laboratory-type spectrometer 24 in transmission mode at room temperature. An open-type X-ray tube equipped with a Analytical Sciences Advance Publication by J-STAGE
doi:10.2116/analsci.19sap03 fatcat:dtwuuf77cbaptgp7p2xy6eigne