Collins Sebastián E, Baltanás Miguel A, Bonivardi Adrian L
Instituto de Desarrollo Tecnológico para la Industria Química (CONICET, UNL), Güemes 3450, S3000GLN Santa Fe, Argentina.
J Phys Chem B. 2006 Mar 23;110(11):5498-507. doi: 10.1021/jp055594c.
The adsorption of CO(2) over a set of gallium (III) oxide polymorphs with different crystallographic phases (alpha, beta, and gamma) and surface areas (12-105 m(2) g(-1)) was studied by in situ infrared spectroscopy. On the bare surface of the activated gallias (i.e., partially dehydroxylated under O(2) and D(2) (H(2)) at 723 K), several IR signals of the O-D (O-H) stretching mode were assigned to mono-, di- and tricoordinated OD (OH) groups bonded to gallium cations in tetrahedral and/or octahedral positions. After exposing the surface of the polymorphs to CO(2) at 323 K, a variety of (bi)carbonate species emerged. The more basic hydroxyl groups were able to react with CO(2), to yield two types of bicarbonate species: mono- (m-) and bidentate (b-) [nu(as)(CO(3)) = 1630 cm(-1); nu(s)(CO(3)) = 1431 or 1455 cm(-1) (for m- or b-); delta(OH) = 1225 cm(-1)]. Together with the bicarbonate groups, IR bands assigned to carboxylate [nu(as)(CO(2)) = 1750 cm(-1); nu(s)(CO(2)) = 1170 cm(-1)], bridge carbonate [nu(as)(CO(3)) = 1680 cm(-1); nu(s)(CO(3)) = 1280 cm(-1)], bidentate carbonate [nu(as)(CO(3)) = 1587 cm(-1); nu(s)(CO(3)) = 1325 cm(-1)], and polydentate carbonate [nu(as)(CO(3)) = 1460 cm(-1); nu(s)(CO(3)) = 1406 cm(-1)] species developed, up to approximately 600 Torr of CO(2). However, only the bi- and polydentate carbonate groups still remained on the surface upon outgassing the samples at 323 K. The total amount of adsorbed CO(2), measured by volumetric adsorption (323 K), was approximately 2.0 micromol m(-2) over any of the polymorphs, congruent with an integrated absorbance of (bi)carbonate species proportional to the surface area of the materials. Upon heating under flowing CO(2) (760 Torr), most of the (bi)carbonate species vanished a T > 550 K, but polydentate groups remained on the surface up to the highest temperature used (723 K). A thorough discussion of the more probable surface sites involved in the adsorption of CO(2) is made.
通过原位红外光谱研究了一系列具有不同晶相（α、β和γ）和表面积（12 - 105 m² g⁻¹）的氧化镓（III）多晶型物对CO₂的吸附情况。在活化氧化镓的裸露表面（即在723 K下于O₂和D₂（H₂）中部分脱羟基），O - D（O - H）伸缩振动模式的几个红外信号被归属于与处于四面体和/或八面体位置的镓阳离子键合的单配位、双配位和三配位OD（OH）基团。在323 K将多晶型物表面暴露于CO₂后，出现了多种（双）碳酸盐物种。碱性更强的羟基能够与CO₂反应，生成两种类型的碳酸氢盐物种：单齿（m - ）和双齿（b - ）[ν（as）（CO₃） = 1630 cm⁻¹；ν（s）（CO₃） = 1431或1455 cm⁻¹（对于m - 或b - ）；δ（OH） = 1225 cm⁻¹]。与碳酸氢盐基团一起，归属于羧酸盐[ν（as）（CO₂） = 1750 cm⁻¹；ν（s）（CO₂） = 1170 cm⁻¹]、桥式碳酸盐[ν（as）（CO₃） = 1680 cm⁻¹；ν（s）（CO₃） = 1280 cm⁻¹]、双齿碳酸盐[ν（as）（CO₃） = 1587 cm⁻¹；ν（s）（CO₃） = 1325 cm⁻¹]和多齿碳酸盐[ν（as）（CO₃） = 1460 cm⁻¹；ν（s）（CO₃） = 1406 cm⁻¹]物种的红外吸收带出现，直至CO₂压力达到约600 Torr。然而，在323 K对样品进行脱气后，只有双齿和多齿碳酸盐基团仍保留在表面。通过体积吸附法（323 K）测量的吸附CO₂的总量，在任何一种多晶型物上约为2.0 μmol m⁻²，这与（双）碳酸盐物种的积分吸光度与材料表面积成正比一致。在流动的CO₂（760 Torr）下加热时，大多数（双）碳酸盐物种在T > 550 K时消失，但多齿基团在所用的最高温度（723 K）下仍保留在表面。对参与CO₂吸附的更可能的表面位点进行了深入讨论。
