Highly Dispersed Ce x Zr1−x O2 Nano-Oxides Over Alumina, Silica and Titania Supports for Catalytic Applications

Abstract

We have been exploring the utilization of supported ceria and ceria-zirconia nano-oxides for different catalytic applications. In this comprehensive investigation, a series of Ce x Zr 1-x O composite oxide catalysts were synthesized and subjected to thermal treatments from 773 to 1073 K to examine the influence of support on thermal stability, textural properties and catalytic activity of the ceria-zirconia solid solutions. The physicochemical characterization studies were performed using X-ray diffraction (XRD), Raman spectroscopy (RS), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HREM), thermogravimetry and BET surface area methods. To evaluate the catalytic properties, oxygen storage/release capacity (OSC) and CO oxidation activity measurements were carried out. The XRD analyses revealed the formation of Ce 0.75 Zr 0.25 O 2 , Ce 0.6 Zr 0.4 O 2 , Ce 0.16 Zr 0.84 O 2 and Ce 0.5 Zr 0.5 O 2 phases depending on the nature of support and calcination temperature employed. Raman spectroscopy measurements in corroboration with XRD results suggested enrichment of zirconium in the Ce x Zr 1-x O 2 solid solutions with increasing calcination temperature thereby resulting in the formation of oxygen vacancies, lattice defects and oxygen ion displacement from the ideal cubic lattice positions. The HREM results indicated a well-dispersed cubic Ce x Zr 1-x O 2 phase of the size around 5 nm over all supports at 773 K and there was no appreciable increase in the size after treatment at 1073 K. The XPS studies revealed the presence of cerium in both Ce 4? and Ce 3? oxidation states in different proportions depending on the nature of support and the treatment temperature applied. All characterization techniques indicated absence of pure ZrO 2 and crystalline inactive phases between Ce-Al, Ce-Si and Ce-Ti oxides. Among the three supports employed, silica was found to stabilize more effectively the nanosized Ce x Zr 1-x O 2 oxides by retarding the sintering phenomenon during high temperature treatments, followed by alumina and titania. Interestingly, the alumina supported samples exhibited highest OSC and CO oxidation activity followed by titania and silica. Details of these findings are consolidated in this review.

A Rapid Microwave-Induced Solution Combustion Synthesis of Ceria-Based Mixed Oxides for Catalytic Applications

“…Figure 10 shows the Si 2p, Ti 2p, Zr 3d and Al 2p photoelectron peaks pertaining to MWCS, MWCT, MWCZ and MWCA samples, respectively. The binding energy of the Si 2p photoelectron peak observed at 103.2 eV for ceria-silica agrees well with the values reported in the literature [88]. However, the poor intensity of the spectra with large peak widths indicates that SiO 2 is not easily accessible at the surface due to the presence of cerium oxide over layer.…”

Dimethyl carbonate synthesis via transesterification of propylene carbonate with methanol by ceria-zinc catalysts: Role of catalyst support and reaction parameters

“…Borgmann and Wedler [38] have reported similar trend of BET surface area for cobalt supported impregnated silica, aluminum and titania catalysts. Reddy et al [25] also observed similar BET surface area trend for aluminum, silica and titania supported ceriazirconia catalyst.…”

“…Metal precursors such as hexahydrates of cerium nitrate and zinc nitrate were dissolved separately in double distilled water with a 1 : 1 molar ratio and mixed together at room temperature. The supporting oxide was dispersed in water, stirred vigorously and thereafter metal precursor cerium-zinc solutions were mixed together [25]. The prepared mixture was diluted with 100 mL of double distilled water and stirred for 1 h. Liquid ammonia was added drop by drop in the mixture under vigorous stirring until the pH reached 8.5.…”

Catalytic Wet Oxidation of Pharmaceutical Sludge by Molecular Sieve Loaded with Cu/Ce

“…The preparation of efficient and durable catalysts is still a challenge. Molecular sieves when supported onto another functional material were exhibited high potential due to their high thermal stability, their relatively high specific surface area and/or their beneficial role in terms of resistance to poisons [5,6]. Many materials containing mainly metals as the precursors supported/intercalated on/in molecular sieves are proposed as catalysts for the oxidation of organic compounds [7,8].…”