Deposition Precipitation Catalyst Research Articles

Influence of 0.25% Indium Addition to Ni/CeO2 Catalysts for Dry Reforming of Methane

In this study, the surface and textural properties as well as the catalytic performance of Ni/CeO2 and NiIn/CeO2 catalysts prepared by wet impregnation (WI) and deposition–precipitation (DP) are investigated. The addition of Ni (3.0 wt.%) resulted in a decrease in the specific surface area and pore volume in the case of the WI method, possibly due to a blockage of mesopores. A minimal addition of In (0.25 wt.%) caused a further decrease in the surface area in both cases. XRD analysis showed that Ni deposited on CeO2 by DP resulted in some lattice incorporation, affecting the crystallinity of the support. The H2-TPR profiles altered depending on the different ways of Ni and In introduction. STEM-EDS-derived elemental maps indicated that the Ni and NiIn particles deposited on CeO2 using the DP method were somewhat smaller than in the WI synthesis. A comprehensive CO-DRIFTS analysis proved a direct Ni-In interaction in bimetallic samples, leading to the formation of a surface NiIn alloy. Ni/CeO2 catalysts showed a higher activity in the process of dry reforming of methane (DRM) than the bimetallic counterparts at 650 °C, with the Ni_DP sample performing slightly better. However, the Ni_DP catalyst showed significant coking, which was drastically reduced by the addition of In. The agglomeration of Ni and/or NiIn particles during the 6 h DRM reaction somewhat impaired the catalyst performance. Overall, this study highlights the intricate relationship between the catalyst preparation, surface properties and catalytic performance in the DRM reaction and emphasizes the beneficial role of In addition in reducing the coking of the monometallic catalyst and the critical location and surface morphology of nickel nanoparticles decorated with indium and in contact with ceria.

Highly Efficient CuO/α-MnO2 Catalyst for Low-Temperature CO Oxidation.

Copper manganese composite (hopcalite) catalyst has been widely explored for low-temperature CO oxidation reactions. However, the previous reports on the stabilization of such composite catalysts have shown that they deactivated severely under moist conditions. Herein, we developed an α-MnO2 nanorod-supported copper oxide catalyst that is very active and stable for the conditions with or without moisture by the deposition precipitation (DP) method. Incredibly, the CuO/MnO2 DP catalyst (with 5 wt % copper loading) achieves superior activity with a reaction rate of 9.472 μmol-1·gcat-1·s-1 even at ambient temperatures, which is at least double times of that for the reported copper-based catalyst. Additionally, the CuO/MnO2 DP catalyst is significantly more stable than the copper manganese composite catalysts reported in the literature under the presence of 3% water vapor as well as without moisture. A correlation between the catalytic CO oxidation activity and textural characteristics was derived via multitechnique analyses. The results imply that the superior activity of the CuO/MnO2 DP catalyst is associated with the proper adsorption of CO on partially reduced copper oxide as Cu(I)-CO and more surface oxygen species at the interfacial site of the catalyst.

Highly-dispersed Ni on BEA catalyst prepared by ion-exchange-deposition-precipitation for improved hydrodeoxygenation activity

BEA zeolite-supported nickel is a promising catalyst for the hydrodeoxygenation reaction. In this study, highly dispersed Ni/BEA catalysts prepared via ion-exchange-deposition-precipitation (IDP) utilising careful pH control were investigated in the hydrodeoxygenation of guaiacol. In comparison, catalysts prepared by incipient wetness impregnation (IWI) and deposition-precipitation (DP) methods were also studied and IDP catalysts were shown to have higher dispersion. Over these carefully prepared catalysts significantly increased selectivity toward hydrocarbons was observed. The presence of nickel hydrides was confirmed by H2-TPD and H2-FTIR. IDP catalyst displays a higher metal dispersion and higher concentration of nickel hydrides than impregnated and DP catalysts, while bigger Ni nanoparticles formed in impregnated catalysts exhibit a higher concentration of nickel hydrides per surface Ni. The guaiacol conversion was not significantly affected by the catalyst preparation method, while the product selectivity was altered. Higher cyclohexane formation rate was detected over IDP catalysts compared to DP and impregnated catalysts. Besides, cyclohexane formation rate displays a positive linear correlation with the concentration of nickel hydrides, suggesting nickel hydrides play a crucial role in the hydrodeoxygenation reaction.

Investigating the dynamic structural changes on Cu/CeO2 catalysts observed during CO2 hydrogenation

CO2 hydrogenation is one route for partial CO2 abatement while producing valuable chemical products. Cu/CeO2 catalysts have attracted great interest as materials that facilitate the efficient hydrogenation of CO2 into methanol and CO. This paper investigates the effect of preparation methods on the structure, function and activity of Cu/CeO2 catalysts. The catalysts have been prepared by deposition–precipitation (DP) and the co-precipitation (CP) methods. The activity tests for the catalysts were conducted in a high-pressure packed bed reactor in the temperature range of 200–300 °C at 50 bar pressure. The DP catalyst showed higher methanol productivity and lower methanol selectivity compared its CP counterpart. The reasons for the higher performance of the DP catalyst and other structural and functional differences have been investigated through in-depth characterization using synchrotron radiated in-situ powder diffraction, DRIFTS, XPS, HR-TEM, TPR and N2O decomposition used to determine copper surface area. The higher methanol productivity in the DP catalyst was attributed to the higher Cu surface area and dispersion. Additionally, the in-situ synchrotron-based powder diffraction measurements provide fundamental insights on the interesting differences in the CeO2 structure i.e. the lattice parameter and the lattice microstrain during the reduction step that could be attributed to the size difference in the CeO2 support nanoparticles.

The Influence of RuO2Distribution and Dispersion on the Reactivity of RuO2−SnO2Composite Oxide Catalysts Probed by CO Oxidation

AbstractTo elucidate the distribution and dispersion of RuO2species on the reactivity, RuO2−SnO2catalysts with 2 % and 5 % Ru contents have been prepared with impregnation (IMP), deposition‐precipitation (DP) and co‐precipitation (CP) methods, and probed by CO oxidation. With IMP and DP methods, RuO2crystallites are predominantly formed on the catalyst surface, which is favorable for CO oxidation. Moreover, the IMP catalyst possesses surface RuO2having smaller mean crystallite size and better dispersion than the DP catalyst, thus SnRuO‐IMP displays higher activity than SnRuO‐DP at the same Ru loadings. However, with CP method, RuO2species is mainly present as Ru4+cations in the lattice of rutile SnO2to form a solid solution structure below the lattice capacity, which is less reactive than the surface RuO2due to the restriction by the SnO2lattice. In conclusion, surface RuO2is revealed to be the active species, whose amount and dispersion determine the activity of the catalysts. By changing preparation methods, the distribution of RuO2species in the catalysts is varied and impacts the reactivity of the catalysts evidently. The traditional impregnation is found to be the best method to prepare RuO2−SnO2, which shows the highest activity among all the catalysts.

Highly Active and Stable Co3O4/ZSM-5 Catalyst for Propane Oxidation: Effect of the Preparation Method

Co3O4 supported on ZSM-5 (Co3O4/ZSM-5) catalysts were prepared by impregnation (IM), deposition precipitation (DP), and hydrothermal (HT) methods. Their catalytic performances for the total oxidation of propane were tested, and their physicochemical properties were investigated by low-temperature N2 adsorption, XRD, FT-IR absorption spectroscopy, XPS, H2-TPR, TEM, and CO chemisorption. The results show that the catalytic activity of Co3O4/ZSM-5 for propane oxidation is higher than that of 1.5 wt % Pd/ZSM-5, and the preparation methods remarkably affect the catalytic activity of Co3O4/ZSM-5. Among four Co3O4/ZSM-5 catalysts prepared by different methods, the catalyst prepared by the HT method possesses the highest catalytic activity for propane oxidation, and their catalytic activities are varied in the order of HT > DP > IM. For the Co3O4/ZSM-5 (DP) catalysts, the precipitant has an evident influence on their catalytic activities. For instance, the DP catalyst prepared with ammonium bicarbonate precipitant has a higher catalytic activity than the catalyst prepared with sodium hydroxide precipitant. The excellent catalytic activity of Co3O4/ZSM-5 (HT) may be attributed to the better reducibility of Co3+, higher Co3+ content, higher surface concentration, and fast migration of the lattice oxygen of Co3O4 on this catalyst. Furthermore, the Co3O4/ZSM-5 catalyst prepared by the HT method exhibits a high stability after being used at 500 °C for 40 h.

Liquid Phase Hydrogenolysis of Biomass‐derived Lactate to 1,2‐Propanediol over Silica Supported Cobalt Nanocatalyst

AbstractLiquid phase hydrogenolysis of ethyl lactate to 1,2‐propanediol was performed over silica supporting cobalt catalysts prepared by two different methods: precipitation‐gel (PG) technique and deposition‐precipitation (DP) procedure. The cobalt species (Co3O4/cobalt phyllosilicate) present in the corresponding calcined PG and DP catalysts were different as a consequence of the preparation methods, and CoOHCo olation and SiOCo oxolation molecular mechanisms were employed to elucidate the chemical phenomena during the different preparation procedures. In addition, the texture (BET), reduction behavior (TPR and in‐situ XRD), surface dispersion and state of cobalt species (XPS), and catalytic performance differ greatly between the samples. Because of small particle size, high dispersion of cobalt species and facile reducibility, the Co/SiO2 catalyst prepared by precipitation‐gel method presented a much higher activity than the catalyst prepared by deposition‐precipitation method. Metallic cobalt is assumed to be the catalytically active site for the hydrogenolysis reaction according to the catalytic results of both cobalt samples reduced at different temperatures and the structure changes after reaction.

Influence of microwave irradiation on catalytic decomposition of nitrous oxide over Rh/Al2O3 catalyst

Abstract Alumina-supported Rh catalysts were prepared by deposition–precipitation (DP) and impregnation (IMP) methods adopting conventional heating (CH) and microwave irradiation (MW), characterized by temperature programmed reduction (TPR), X-ray diffraction, XRD, CO-diffuse reflectance infrared Fourier transform spectroscopy (CO-DRIFTS) techniques and evaluated for their activity in N 2 O decomposition. The activity of the DP catalyst was found to be significantly higher than the IMP catalyst, which was manifested in the formation of electron deficient Rh species, as observed by CO-DRIFTS analysis. MW irradiation further enhanced the number of the Rh active sites. A combination of DP and MW irradiation produced a catalyst with a superior activity than that prepared by either of the methods.

Characterization of bamboo-shaped CNTs prepared using deposition-precipitation catalyst

The deposition-precipitation method was employed to prepare the Ni/Al catalyst precursor, Ni(OH) 2/Al, which was then calcined and reduced to form Ni/Al catalyst. The results showed that the active nickel nanoparticles were uniform in size with the diameters of 10–20 nm. After the catalytic decomposition of methane, a mass of multi-walled carbon nanotubes (CNTs) have been synthesized. The diameters of the CNTs were also in the range of 10–20 nm and the high-resolution transmission electron microscope images exhibited that the CNTs have a bamboo-shaped structure. X-ray photoelectron spectroscopy characterization on the CNTs showed that the base-growth mode predominated in the deposition-precipitation catalyst and the nitrogen as a carried gas could stimulate the formation of the bamboo-shaped CNTs.

Direct decomposition of nitrous oxide over Ru/Al2O3 catalysts prepared by deposition–precipitation method

Abstract Alumina-supported ruthenium catalysts were prepared by the deposition–precipitation (DP) and impregnation (IMP) methods. The catalysts were characterized by BET surface area, X-ray diffraction, temperature-programmed reduction (TPR) and diffused reflectance infra-red spectroscopic (DRIFTS) techniques. The DP catalysts showed higher activity than their IMP analogues. The DRIFTS analysis revealed preferential formation of Ru n + species on the surface of DP catalysts. Both Ru n + and Ru 0 species appeared on IMP catalysts, with the composition of Ru 0 increasing with increase in metal loading. The temperatures at which the peak maxima appeared were higher in the TPR patterns of the DP catalysts, indicating greater interaction between Ru and alumina, which explained the formation of the cationic Ru species. The high activity of the catalysts prepared by DP method was related to the formation of electron deficient Ru sites during the preparation of the catalyst.

XPS study of supported gold catalysts: the role of Au0 and Au+δ species as active sites

AbstractGold nanoparticles supported on different oxides (SiO2, CeO2 and TiO2) were prepared by the SMAD (solvated metal atom dispersion) and deposition–precipitation (DP) techniques. The physical and chemical characterization of the catalysts was performed by X‐ray photoelectron spectroscopy (XPS) and X‐ray diffraction (XRD) and the catalytic activity was tested during the reaction of low temperature CO oxidation. The structural and surface analyses evidenced the presence of small gold crystallites (cluster size ∼2–5 nm) in all the SMAD‐prepared samples and oxidized gold species in the case of the DP catalysts. A different surface distribution of ionic gold species was found on the different supports. By comparing the catalytic activities of the samples, the presence of Au+1 species seems to be the main requisite for the achievement of the highest CO conversion at the lowest temperature. The higher activity of Au/CeO2(DP) catalysts at T ≈ 250 K can be ascribed to a better stabilization of the AuO− species by the cerium oxide. Nanosized metallic gold particles exhibit a worse catalytic performance, both on ‘reducible’ and ‘inert’ supports, being significantly active only in the temperature range: 400–600 K. Copyright © 2006 John Wiley & Sons, Ltd.

Metal-support and preparation influence on the structural and electronic properties of gold catalysts

Nanostructured gold catalysts supported on CeO 2 and SiO 2 were prepared by the deposition–precipitation (DP) and the solvated metal atom dispersion (SMAD) techniques. The structural and electronic properties of the catalysts were investigated by X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS). Gold was found as small metal nanoparticles (cluster size ∼2 nm) in the SMAD-prepared samples and in ionic state in the DP catalysts. The catalytic activity of the samples was tested in the reaction of low temperature CO oxidation. Gold nanosized particles in a pure metallic state exhibited a worse catalytic performance, both on ceria and silica. The presence of non-metallic Au species seems to be the main requisite for the achievement of the highest CO conversion at the lowest temperature. The higher activity of the Au/CeO 2 (DP) sample with respect to the Au/SiO 2 (DP) catalyst can be ascribed to a better stabilization of the Au +1 ions, probably as AuO - species, by the cerium oxide.

Low-temperature catalytic combustion of methane over Pd/CeO 2 prepared by deposition–precipitation method

Ceria supported 2 wt% Pd catalysts for low-temperature methane combustion were prepared by the impregnation (IM) and deposition–precipitation (DP) methods, which are denoted as Pd–IM and Pd–DP, respectively. DP was found to be an available method for achieving high activity and stability of the Pd/CeO 2 catalyst. The temperatures for methane ignition ( T 10%) and total conversion ( T 100%) over Pd–DP are 224 and 300 °C at GHSV of 50,000 h −1, which are 83 and 110 °C lower than the corresponding temperatures of Pd/Al 2O 3. X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS) analyses show that palladium species in Pd–DP is highly dispersed, positively charged and difficultly reduced. Raman spectra disclosed that the largest concentration of defects and/or oxygen vacancies was formed in Pd–DP catalyst. A kind of cationic PdO δ+ sites with higher binding energies than PdO are in close vicinity to the oxygen vacancies in the CeO 2 support and might act as the active centers for methane oxidation. Furthermore, the deactivation and steam aging tests for Pd–DP showed that the performance of this type of palladium was very stable and could be repeatedly recovered after several long time aging tests.

Catalytic and noncatalytic CO oxidation on Au/TiO 2 catalysts

The CO oxidation reaction has been studied on Au/TiO 2 catalysts prepared by incipient wetness (IW) and deposition–precipitation (DP) methods, with a range of metal loadings from 0.1 to 5 wt% for the former. We have found that there are three types of CO 2 production from fresh catalysts which have been calcined to only 120 °C, namely noncatalytic (types I and II) and catalytic (type III). The DP catalysts are far more active for type III reaction, showing activity at room temperature, whereas the IW catalysts generally do not show steady-state conversion until >120 °C. However, IW catalysts with low loadings produce type I CO 2 (that formed at room temperature), whereas higher loadings produce only type II (that formed when heating), with intermediate loadings showing both. We associate type I CO 2 production with monolayer Au catalysts, which have intimate contact with the TiO 2, and are probably already in some oxidic form. Type II behavior we associate with three-dimensional oxidic Au, the surface of which is no longer in direct contact with the support. The poor performance of IW catalysts compared with DP catalysts is ascribed to the presence of chloride in the former, which induces a larger average particle size, and vulnerability to extensive sintering.