Catalytic Activity In Water-gas Shift Reaction Research Articles

Influence of gold presence and thermal treatment on recrystallization of copper-manganese ferrite catalysts

The present work aims to evaluate the influence of synthesis conditions and gold addition on structural and functional characteristics of copper-manganese ferrites. Object of the investigation is spinel ferrite with composition Cu0.5Mn0.5Fe2O4, thermally treated at different conditions. The influence of gold deposition on structure of ferrites and catalytic properties in water-gas shift reaction (WGSR) is studied on the ferrite sample obtained at 300 ∘C. Structural characteristics of samples are determined by Mossbauer spectroscopy and X-Ray diffraction. The Mossbauer spectra of treated at different temperature ferrite samples consist of sextet and doublet components. A comparative assessment of crystallite size of ferrite phase was accomplished from the calculated value of the hyperfine fields. It was established well expressed tendency of ferrite crystallite growth with increasing of thermal treatment temperature. Increasing of the ferrite crystallite size in presence of gold in the sample is established, too. The analysis of catalytic activity in WGSR shows unexpected result i.e. the activity of gold-modified ferrite sample is lower than that of the sample without gold. Probably this is due to complex factors, including recrystallization of the ferrite phase due to additional thermal treatment at higher temperature, addition of gold, changes of the structural features and phase composition during catalytic test.

The impact of synthesis method of CNT supported CeZrO2 and Ni-CeZrO2 on catalytic activity in WGS reaction

Carbon nanotube (CNT) supported catalysts containing ceria-zirconia mixed oxide (CeZrO2) and nickel were synthesized and tested in water gas shift (WGS) reaction. Physicochemical characterization including N2 adsorption, X-ray diffraction (XRD), scanning and transmission microscopy (SEM/TEM), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and temperature programmed reduction with H2 (H2-TPR), as well as catalytic tests of WGS reaction showed that the synthesis method had significant impact on composition, morphology, structural properties and catalytic performance of obtained hybrid materials. The catalysts obtained by co-precipitation of metal oxides (NiO and/or CeZrO2) on CNT walls demonstrated better dispersion of active phase and smaller particle size than catalyst obtained by depositing of powder CeZrO2 or Ni-CeZrO2. Moreover, the catalyst obtained by co-precipitation revealed better performance in WGS reaction; however, some CH4 formation was noticed over Ni-CeZrO2/CNT system. The role of CeZrO2 in catalysts performance in WGS as well as the importance of good metal-oxide contact were confirmed.

Nanostructured Pd modified Ni/CeO2 catalyst for water gas shift and catalytic hydrogen combustion reaction

Nanostructured Pd-modified Ni/CeO2 catalyst was synthesized in a single step by solution combustion method and characterized by XRD, TEM, XPS, TPR and BET surface analyzer techniques. The catalytic performance of this compound was investigated by performing the water gas shift (WGS) and catalytic hydrogen combustion (CHC) reaction. The present compound is highly active and selective (100%) toward H2 production for the WGS reaction. A lack of CO methanation activity is an important finding of present study and this is attributed to the ionic substitution of Pd and Ni species in CeO2. The creation of oxide vacancies due to ionic substitution of aliovalent ions induces dissociation of H2O that is responsible for the improved catalytic activity for WGS reaction. The combined H2-TPR and XPS results show a synergism exists among Pd, Ni and ceria support. The redox reaction mechanism was used to correlate experimental data for the WGS reaction and a mechanism involving the interaction of adsorbed H2 and O2 through the hydroxyl species was proposed for CHC reaction. The parity plot shows a good correspondence between the experimental and predicted reaction rates.

Zirconia modified monolithic macroporous Pt/CeO 2/Al 2O 3 catalyst used for water-gas shift reaction

Monolithic macroporous Pt/CeO 2/Al 2O 3 and zirconia modified Pt/CeO 2/Al 2O 3 catalysts were prepared by using concentrated emulsions synthesis route. The catalytic performances over the platinum-based catalysts were investigated by water-gas shift (WGS) reaction in a wide temperature range (180–300 °C). The samples were characterized with thermogravimetry (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and temperature programmed reduction (TPR) techniques as well. The SEM and HRTEM results indicated that the monoliths possessed macroporosity, in size of 5–50 μm, and platinum particles were homogeneously dispersed on macroporous materials. XRD and TPR results showed that the interaction between ceria and zirconia oxide was formed and the addition of zirconia could promote the reducibility of platinum oxide on the interface of ceria and zirconia particles, which led to an improvement of catalytic activity in WGS reaction. The results indicated that zirconia modified monolithic macroporous Pt/CeO 2/Al 2O 3 could be fabricated in small size (from millimeter lever to centimeter) and had good reaction activity, which was a potential new route for miniaturization of the WGS reactor.

FTIR study of low-temperature water-gas shift reaction on gold/ceria catalyst

Chemisorption and reactivity of the molecules involved in the water-gas shift (WGS) reaction on gold/ceria catalyst have been studied at 90 and 300 K by FTIR spectroscopy. Forward and reverse WGS reaction at 300 K and up to 573 K have been investigated, too. The FTIR results show that gold causes a strong modification of the surface properties of the support. The nanosized metallic gold particles in close contact with defective ceria play an essential role for the genesis of high catalytic activity in WGS reaction at low temperature and appear to be of crucial importance in explaining the remarkably high stability of this catalytic system. An electronic interaction between small gold metallic nanoparticles and ceria has been evidenced.

The behaviour of Ru/Fe 2O 3 catalysts and Fe 2O 3 supports in the TPR and TPO conditions

The texture of Fe 2O 3 support and Ru/Fe 2O 3 catalysts supported on iron oxides obtained from β-FeOOH (B) or δ-FeOOH (D) and their catalytic activity in WGSR were studied. Also their susceptibilities to reduction and reoxidation, were studied by TPR, using H 2 or CO and TPO methods. In the case of TPR CO the composition of the reducing mixture containing traces of H 2O enabled investigation of water gas shift reaction (WGSR). The catalysts from series D were found more readily reducible and oxidised than those from series B. The supported ruthenium enhanced the redox effects and caused the appearance of additional effects related directly to its presence. Depending on the kind of support and on ruthenium presence considerable differences in temperatures of WGSR onset were found. It is suggested that the susceptibility of the catalysts to reduction and oxidation is responsible for their activity in the WGSR.