Structure Analysis of Al-Modified TiO₂ Nanocatalyst Supports

Abstract

The structures of Al-modified anatase TiO 2 supports were analyzed using traditional analysis techniques of X-ray diffraction, transmission electron microscopy, and N 2 sorption as well as X-ray absorption near-edge spectroscopy, 27 Al magic-angle spinning NMR, and low-temperature heat capacity. The combined results from these characterizations reveal that the Al dopant is incorporated either on the surface or in vacancies depending on the details of the synthetic method used. Alumina incorporated on the surface stabilizes TiO 2 by lowering the surface energy of anatase and stabilizing planes with high surface energy that would otherwise join to achieve a reduced surface energy. On the other hand, Al incorporated in TiO 2 vacancies stabilizes the structure through increasing lattice strain and limiting mass transport necessary for grain growth. The 22 mol % Al-modified TiO 2 with Al on the surface had average crystallite diameter of 6 nm, surface area of 184 m 2 g −1 , pore volume of 0.34 cm 3 g −1 , and pore diameter of 6.4 nm compared with the 22 mol % Al-modified TiO 2 with Al incorporated in vacancies and on the surface which had average crystallite diameter of 2− 3 nm, surface area of 471 m 2 g −1 , pore volume of 0.44 cm 3 g −1 , and pore diameter of 4.4 nm. This work demonstrates the importance of structure analysis of doped nanomaterials in the development of stabilized catalysts and catalyst supports.

Rapid Synthesis of C-TiO2: Tuning the Shape from Spherical to Rice Grain Morphology for Visible Light Photocatalytic Application

“…The spherical morphology (CT-1) of C-TiO 2 shows a sharp decline in the desorption branch indicating its mesoporosity, whereas the hysteresis (Type-IV, H1) between the two curves suggests the pores to have a diffusion bottleneck structure. 41 The following parameters were estimated for CT-1: surface area 62 m 2 /g, pore volume 0.24 cc/g, and BJH pore diameter 18.0 nm. In addition, it showed a unimodal pore size distribution that was a little broad in the range due to its spherical morphology.…”

Fabrication of highly homogeneous Al‐doped TiO2 nanotubes by nanolamination of atomic layer deposition

“…Recently, there has been a growing interest in fabricating advanced functional nanocomposites which display superior physical, chemical, or mechanical properties compared to their bulk constituents. The Al 2 O 3 –TiO 2 system has drawn extensive attractions because it has been widely used as a support material in the field of catalysis.…”

“…The Al 2 O 3 –TiO 2 system has drawn extensive attractions because it has been widely used as a support material in the field of catalysis. Modifying or stabilizing with the dopant of Al is regarded as an effective strategy for promotion of thermal stability, surface area, and porosity of TiO 2 . Besides, TiO 2 with the high dielectric constant (ĸ>40) and refractive index (n>2.4) has been considered as a promising material for the capacitor of dynamic random access memory (DRAM) .…”

“…However, according to the binary TiO 2 –AlO 1.5 phase diagram (Figure ), except the compound Al 2 TiO 5 , there is essentially no solubility of Al 2 O 3 in TiO 2 at T <1200 K, even though many studies based on the “nominal composition” of Al‐doped TiO 2 have been reported. With conventional synthesis methods, the dopants might be present in TiO 2 in a number of ways besides solid solution, such as surface species or intermixed segregated phases . In order to address and clarify this issue, the present work fabricated nanolaminated multi‐layers of Al 2 O 3 and TiO 2 with each thickness less than a nanometer by the atomic layer deposition (ALD) process.…”

Al- and Ga-Doped TiO2, ZrO2, and HfO2: The Nature of O 2p Trapped Holes from a Combined Electron Paramagnetic Resonance (EPR) and Density Functional Theory (DFT) Study

“…Al-doped ZrO 2 has been investigated also for logic devices and for resistive memories. More traditional areas where Al or Ga impurities have been introduced in titania are those of catalysis 9 and photocatalysis 10,11,12,13 or in the design of dye-sensitized solar cells. 14 The purpose is that to increase the surface activity of the oxides or to enhance the capture of solar light for photoinduced processes, thanks to the presence of the dopants.…”