Impregnation Order Research Articles

Impact of the incipient wetness impregnation sequence during the preparation of La or Ce promoted NiCu-Al2O3 on low-temperature hydrodeoxygenation

The performance of La- or Ce-promoted NiCu-Al2O3 catalysts in the low-temperature (200 °C) hydrodeoxygenation (HDO) is assessed. Co-impregnation of the promoter with NiCu does not affect the bulk structure, although the catalytic activity of the Ce-promoted catalyst increases due to strong NiCu-Ce interactions. For sequential impregnation, the impregnation order for Ce improves either the HDO selectivity or the activity. For La, both sequentially impregnated catalysts exhibit an improved HDO selectivity, but a different activity. First impregnating La is especially interesting due to the catalysts enhanced stability after an initial deactivation period of 30 h TOS.

Study of the impregnation sequence of active phase and effect of cobalt content over Co-CeO2/MgΑl2O4 catalysts in ethanol steam reforming

Co–CeO2/MgAl2O4 catalysts were obtained by varying the impregnation order (sequential or co‒impregnation) of active phase (Co) and Ce and were evaluated in the ethanol steam reforming (ESR) reaction. Results from TPR and XPS revealed that the impregnation order influenced the metal‒metal and/or metal‒support interactions and Co0/Con+, Ce3+/Ce4+ and the Co/Ce surface molar ratio, affecting the catalyst behavior in the ESR reaction. The solids prepared by sequential impregnation, Co/Ce/S and Ce/Co/S exhibited a greater degree of reduction than the solid obtained by co‒impregnation (CoCe/S), though these systems displayed low dispersion of Co species and low content of surface Co°. The solid CoCe/S showed the highest dispersion (68.5%) and greater presence of Co0 on the surface. The effect of the cobalt content (4, 8 and 12 wt%) was also examined in catalysts prepared using the co‒impregnation method. With the increase in cobalt content, a greater loss of stability and a greater amount of carbon deposits were observed. The highest H2 yield (5.3 mol H2/mol C2H5OH) and stability were achieved over the solid obtained by co‒impregnation with 8 wt% Co, which was attributed to the high dispersion of the active phase and its high content of surface metallic cobalt.

Analysis by temperature-programmed reduction of the catalytic system Ni-Mo-Pd/Al2O3

Alumina-supported nickel catalysts are used to facilitate many reactions at various scales. However, the deactivation of these catalysts is an important problem that has prompted the search for solutions such as the addition of other metals that act as promoters. In this research, the interactions that form between the support and the metals have been studied, a fundamental property that directly affects the performance of the catalyst. With this idea, several Ni-Pd and Ni-Mo bimetallic and various Ni-Mo-Pd trimetallic samples have been prepared, and the reduction capacity of the oxide phases by temperatura-programmed reduction has been analyzed and studied. It has been found that in bimetallic catalysts, Pd favors the appearance of NiO species that are more easily reducible than Mo. In the same way, the data obtained from the trimetallic simples suggest that the impregnation order of Mo and Pd is not a determining factor in these catalysts. In addition, it has been found that the co-impregnation of Ni with Pd gives better results than the sequential impregnation of these metals. The results obtained have also shown that the order of nickel impregnation is decisive. In the case of Ni-Mo catalysts, by impregnating the molybdenum first, catalysts with better reducing properties can be obtained.

Comprehensive Model for the Synthesis of γ-Al2O3 Microsphere-Supported Bimetallic Iron- and Copper Oxide Materials.

The effects of incipient wetness impregnation synthesis conditions on the macro- and microscopic properties of bimetallic iron oxide/copper oxide@γ-Al2O3 microspheres were elucidated. The key steering factors for the macroscopic distribution of the metals throughout the support, and for the metal nanoparticle sizes, were the pH of the impregnation solution, the counterions present in the metal precursor, the amount of negatively charged groups on the alumina, the complexation of iron, the impregnation strategy (simultaneous or sequential) and, in the latter case, the order of impregnation. The interactions taking place during impregnation are identified as competitive adsorption of charged dissolved species (Fe/Cu cations, protons, and additional anions) in the impregnation solution. Adsorption can take place on either charged alumina sites or previously deposited metal (i.e., iron on iron, copper on copper, iron on copper, and copper on iron) and is affected by counterion shielding. Modeling of these interactions via simulation on an in-house-developed python code allowed quantification of the adsorption constants for each of the above-mentioned processes, where iron adsorbs much faster than copper on all surfaces, and adsorption of iron on both alumina surface groups and previously deposited copper contributes majorly to the final iron distribution. The findings in this work will allow for better prediction and control over bimetallic materials synthesized via the simple and scalable impregnation procedure.

Activity and Stability of Pd Bimetallic Catalysts for Catalytic Nitrate Reduction

In this work, we study the effect of modifying the metal loading (0.5–1.5 wt.% Pd and 0.1–1 wt.% Sn or In), the impregnation order of noble or promoter metal (Pd–Sn or Sn–Pd), and the type of promoter metal (Sn or In) during the preparation process for a Pd bimetallic catalyst, supported on γ-alumina, used in the catalytic reduction of nitrate. The deposition of the noble metal over the promoter metal, especially with Pd:Sn ratios (wt.) of 1:10 and 1:2, favored the hydrogen spillover rate and increased the H concentration on the catalyst surface, enhancing NH4+ production. On the other hand, Pd–In catalysts showed higher activity than the Sn catalysts, as well as higher NH4+ selectivity. The stability of the Pd–Sn/Al2O3 (1.5–1 wt.%) catalyst was evaluated in long-term experiments for the treatment of synthetic water (100 mg L−1 NO3−) and three different commercial drinking waters. This Pd–Sn/Al2O3 catalyst achieved a stable nitrate conversion for a duration of 50 h in the synthetic water treatment. However, the catalyst showed a significant activity loss in the presence of other ions (different to NO3−) in the reaction medium, increasing slightly the selectivity to NH4+.

Single-walled carbon nanotube buckypaper as support for highly permeable double layer polyamide/zeolitic imidazolate framework in nanofiltration processes

The development of membranes for nanofiltration applications requires not only selective layers but also suitable supports to control their synthesis as well as to enable efficient and competitive membrane performances. Single-walled carbon nanotube free-standing films (denoted as buckypaper) have been used as supports for the preparation of polyamide (PA) layers by interfacial polymerization (IP) and tested for dead-end nanofiltration for dyes removal (265–1017 Da) from water and organic solvents. The arrangement of the phases during the IP is essential, thus impregnation on the buckypaper support, first with the organic phase and then with the aqueous phase (denoted as inverse IP, iIP) leads to permeances (of up to 28.0 and 31.4 L m−2 h−1 bar−1 for water and methanol, respectively) and rejection values (>96%) that exceed those of the membranes prepared by reversing the impregnation order. Secondly, a double layer PA/zeolitic imidazolate framework (ZIF-8 or ZIF-93) was prepared on the buckypaper (bp). The design of this double layer led to superior membrane performance, in particular for the hydrophilic ZIF-93, as it changes the PA layer properties (increasing both hydrophilicity and surface roughness) providing higher permeances (up to 59.3 and 76.0 L m−2 h−1 bar−1 for water and methanol, respectively) and dye rejections (>98.5%) than the bare PA layer prepared by iIP. This attractive performance of the PA/ZIF-93/bp membrane has been corroborated with experiments in cross-flow nanofiltration and dead-end nanofiltration of aqueous salt solutions, long-term stability nanofiltration and the study the membrane separation performance after a chlorine treatment. The results reported here therefore show the enormous potential of these membrane architectures for a variety of selective separation processes.

Influence of Fe‐modified Mn–Ce–Fe–Co–Ox/P84 catalytic filter materials for low‐temperature NO removal synergistic Hg0oxidation

AbstractA series of Mn–Ce–Fe–Co–Ox/P84 (polyimide) catalytic filter materials by in situ method (ISM) were investigated for the low‐temperature catalytic activities for NO and elemental mercury Hg0in the simulated flue fixed‐bed system, especially under mixed atmosphere conditions with water and sulfur. The influence of Fe and Co doping ratio, Fe of loading sequence, and the types of precursors are systematically investigated under 8% H2O and 75 ppm SO2atmosphere. Results showed that the toxic effects of H2O and SO2on the catalytic filter materials were obvious. When using Mn–Ce–Fe–Co–Ox/P84 catalytic filter materials (Mn/Ce/Fe/Co = 4:5:0.5:0.5, in mol), the NO reduction and Hg0oxidation decreased from 95.0% to 40.0% and 55%, respectively. As the molar ratio of Fe/Co increased, the anti‐sulfur and water resistance activity of catalytic filter materials showed a trend of first increasing and then decreasing. Active components of Mn–Ce–Fe–Co–Ox/P84 (Mn/Ce/Fe/Co = 4:5:1.25:1 in mol) could achieve 81.0% of NO reduction and 79.2% Hg0oxidation simultaneously. As the molar ratio of Fe/Co increased, the NOxsynergistic Hg0conversion efficiency of the catalytic filter materials was first promoted and then suppressed. Comparing the order of Fe impregnation and the types of Fe precursors revealed that using Fe(NO3)3to generate Fe2O3was more active than directly using Fe2O3at 170°C to 260°C. Electron transfer between Mn, Ce and Fe increases the high ratio of Mn4+/(Mn4++Mn3+) and Ce3+/(Ce3++Ce4+) which may enhance the sulphur and water resistance of the catalytic filter materials.

Exploring the reasons for Zr-improved performance of alumina supported cobalt fischer-tropsch synthesis

In order to investigate the enhancement of Zr in FTS performance, a series of Zr-modified 20 wt% Co/Al2O3 catalysts has been prepared by regulating the Zr and Co impregnation order and Zr amount and then the catalytic performance were evaluated in a fixed reactor. The Zr addition leads to a significant increase in activity, olefin/paraffin ratio for C3 and C4 at a similar CO conversion, and selectivity to C5+ compared with the Co/Al2O3 catalysts. The co-impregnation of Zr and Co shows the most attractive catalytic performance. This can be attributed to the higher reducibility of the catalyst as well as the formation of Co–Zr interface. The introduction of Zr can enhance the interaction between C∗ and cobalt active sites and weaken the CO bond, making CO easier to be dissociated and the selectivity of C5+ is improved.

The effects of MoO3 impregnation order on the catalytic activity for propane combustion over Pt/ZrO2 catalysts: the crucial roles of Pt–MoO3 interfacial sites density

MoO3 promoted Pt/ZrO2 catalysts were prepared by co-impregnation (Pt–Mo/ZrO2) or stepwise impregnation (Pt/Mo/ZrO2 and Mo/Pt/ZrO2) for propane combustion.

Direct conversion of ethylene to propylene based on molybdenum catalysts

The series of molybdenum catalysts prepared by the incipient wetness impregnation of porous alumina with a different impregnation order of the NiO (PdO) and MoO3 precursors was studied in the direct conversion of ethylene to propylene. The maximum propylene yield (28 wt.%) was achieved at 70 °C MoO3/PdO/Al2O3 catalyst obtained by sequential impregnation of the palladium precursor and then the molybdenum precursor. The samples containing stable oxidized forms of palladium or bonded to the surface of the support nickel cations exhibited a high activity in ethylene conversion. It was found that palladium-containing catalysts were more selective than nickel-containing, probably due to an easier formation of reduced active molybdenum sites in the presence of palladium.

Fabrication of Ce-Promoted Ni/Al₂O₃ Methane Steam Reforming Catalysts by Impregnation.

CeO₂-promoted Ni/Al₂O₃ catalysts were fabricated by impregnation. The effects of the CeO₂ promotion and impregnation order on the microstructural evolution and catalytic durability were investigated for methane steam reforming. The CeO₂-promoter nanoparticles resulted in good dispersion and reduced particle size of Ni catalysts. The enhanced durability of CeO₂-promoted Ni/Al₂O₃ catalysts might be associated with the depression of carbon deposition by the presence of CeO₂-promoter nanoparticles.

Oxidative Esterification of 5‐Hydroxymethylfurfural under Flow Conditions Using a Bimetallic Co/Ru Catalyst

AbstractFuranic di‐carboxylate derivatives of 5‐Hydroxymethylfurfural (HMF) are nowadays important in the polymer industry as they are used as building blocks for bio‐based polyesters. The high reactivity of HMF compels to avoid harsh synthetic conditions. Therefore, developing mild catalytic processes for its selective oxidation is a challenging task. Herein, we report the first oxidative esterification of HMF to dimethyl furan‐2,5‐dicarboxylate (FDCM) under flow conditions using oxygen as oxidant. For that purpose, a new series of nitrogen‐doped carbon‐supported bimetallic Co/Ru heterogeneous catalysts were prepared and characterized by XRD, XPS and N2 physisorption. These analyses revealed that the porosity of the materials and order of impregnation of the metals to the carbon supports lead to varying catalytic activities. Under optimized conditions the flow reactor showed a 15‐fold increase on the production of FDCM compared to batch conditions.

Cu location onto spherical SiO2@Mn make a profound difference for catalytic oxidative removal Na2S in waste water with air as an oxidant at ambient conditions

Different location Cu species on the SiO2@Mn catalysts surface was prepared to form well-defined core-shell material for enhancing the catalytic efficiency of degrading Na2S in waste water. The modified location of Cu species was tuned through changing the order of impregnation. The species of Cu in the middle layer perform the best activity and selectivity. Integrating XRD, HAADF-STEM, H2-TRP, UV–vis, XPS, CV and Na2S removal tests, the decisive factor for improved the catalytic efficiency for Na2S removal probably is the unique structural advantages of Cu species in the middle layer, which produces higher ratio of Mn4+/(Mn4+ + Mn3+) and provides rich surface active oxygen. And Na2S in waste water could be degraded as high as 92.77% in 4 h with air as an oxidant at ambient conditions. Recycling experiments indicate that no significant deactivation occurred for the catalysts during tests in seven times. This work provides a novel sight for preparing high-efficient and stable catalysts for Na2S degradation.

Silver/Platinum Supported on TiO2 P25 Nanocatalysts for Non-photocatalytic and Photocatalytic Denitration of Water

Denitration of water was investigated by non-photocatalytic and/or photocatalytic processes (UV-A irradiation at 365 nm) using a mixture of Ag/P25 + Pt/P25 monometallic catalysts and Ag–Pt(Pt–Ag)/P25 bimetallic catalysts (2 wt% Ag; 4 wt% Pt) prepared by drop-wise wetness impregnation of TiO2 P25 support. In the bimetallic samples, the influences of the Pt precursor (H2PtCl6·6H2O; K2PtCl6) and of the impregnation order of the metallic salts were examined. The highest N2 yield (42.3%) in the non-photocatalytic process was achieved with the Ag/P25 + Pt/P25 mixture but with ca. 12.6% NO2 − yield. Photocatalytic activity was enhanced in presence of H2 in comparison to H2-free condition. Ag/P25 is the most active photocatalyst, however high NO2 − yield is obtained (32.5%). The bimetallic samples exhibit high versatility, being active both in the non-photocatalytic and the photocatalytic processes. Low NO3 − conversion and high NO2 − selectivity results were obtained from impregnation of Ag first. In contrast, impregnation of Pt precursor from K2PtCl6 first effectively promoted NO3 − reduction towards N2 yield of 36% and particularly low NO2 − yield of 2.7%, due the presence of metallic nanoparticles of different sizes and interaction with TiO2 with a peculiar strong Pt and Ag interaction. Best results obtained in non-photocatalytic and photocatalytic processes are almost similar.

Effect of Rh Addition to Ni/MgO-Al2O3 Catalysts for Dry Reforming of Methane

Objective: This study has analyzed the performance of Ni and Ni-Rh catalysts based on MgO/g-Al2 O3 in the process of dry reforming of methane (DRM). Methods/Statistical Analysis: The samples were prepared using the incipient wetness impregnation method and were characterized by N2 adsorption, X-ray diffraction (XRD), temperature-programmed reduction (TPR), diffuse reflectance spectroscopy (DRS), surface acidity, X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis (TGA), and Raman spectroscopy. The catalysts were reduced with hydrogen and measured in the reaction of CH4 with CO2 at two CH4 /CO2 ratios. Findings: The 0.5% Rh addition to Ni/MgO-g-Al2 O3 improves the activity and the stability for this process. In the bimetallic catalysts, the reduction temperature of the active phase decreases due to the hydrogen spillover mechanism from the noble metal to the catalyst surface, which favors their catalytic activity. On the other hand, the interaction between Rh and the support would be the cause for the better performance of bimetallic catalysts. The Rh-Ni/MgO-g-Al2 O3 catalyst is the most active, indicating that the impregnation order affects the catalytic behavior. Improvements/Applications: This study gives promising results for this type of catalyst, also showing the effect of the catalyst preparation on the activity and its relationship with deactivation by coke. Keywords: Dry Reforming of Methane, Oxides, Rh-Ni Catalysts, Raman Spectroscopy and Scattering, Surface Properties

Metal effects in Mn-Na2WO4/SiO2 upon the conversion of methane to higher hydrocarbons

The roles of Na, Mn, W and silica, and the synergistic effects between each metal in the <TEX>$MnNa_2WO_4/SiO_2$</TEX> catalyst have been investigated for oxidative coupling of methane (OCM). The crystallisation of amorphous silica during calcination at <TEX>$900^{\circ}C$</TEX> was promoted primarily by Na, but Mn and W also facilitated this process. The interaction between Na and Mn tended to increase the extent of conversion of <TEX>$Mn_3O_4$</TEX> to <TEX>$Mn_2O_3$</TEX>. The formation of <TEX>$Na_2WO_4$</TEX> was dependent on the order in which Na and W were introduced to the catalyst. The impregnation of W before Na resulted in the formation of <TEX>$Na_2WO_4$</TEX>, but this did not occur when the impregnation order was reversed. <TEX>$MnWO_4$</TEX> formed in all cases where Mn and W were introduced into the silica support, regardless of the impregnation order; however, the formation of <TEX>$MnWO_4$</TEX> was inhibited in the presence of Na. Of the prepared samples in which a single metal oxide was introduced to silica, only <TEX>$Mn/SiO_2$</TEX> showed OCM activity with significant oxygen conversion, thus demonstrating the important role that Mn plays in promoting oxygen transfer in the reaction. The impregnation order of W and Na is critical for catalyst performance. The active site, which involves a combination of Na-Si-W-O, can be formed in situ when distorted <TEX>$WO_4^{2-}$</TEX> interacts with silica during the crystallisation process facilitated by Na. This can only occur if the impregnation of W occurs before Na addition, or if the two components are introduced simultaneously.

2-10 逐次含浸法で調製したCo/SiO_2触媒のFT合成活性と表面構造に及ぼす含浸順序の影響((3)天然ガス転換技術1,Session 2 天然ガス・メタンハイドレート等)

2-10 逐次含浸法で調製したCo/SiO_2触媒のFT合成活性と表面構造に及ぼす含浸順序の影響((3)天然ガス転換技術1,Session 2 天然ガス・メタンハイドレート等)

Roles of Promoters in V2O5/TiO2 Catalysts for Selective Catalytic Reduction of NOx with NH3: Effect of Order of Impregnation.

Recently, various promoters for commercial selective catalytic reduction (SCR) catalysts are used to improve DeNOx activity at low temperature. We aimed at finding the optimum condition to prepare V2O5/TiO2 catalyst by changing promoters (W, Ce, Zr and Mn), not only for improving SCR reactivity, but also for reducing N2O formation at high temperature. In addition, we changed the order of impregnation between promoter and vanadium precursors on TiO2 support and observed its effect on activity and N2O selectivity. We utilized various analytical techniques, such as N2 adsorption-desorption, X-ray Diffraction (XRD), Raman spectroscopy, UV-visible Diffuse Reflectance Spectroscopy (UV-vis DRS) and Temperature Programmed Reduction with hydrogen (H2-TPR) to investigate the physicochemical properties of V2O5/TiO2 catalysts. It was found that W and Ce added V2O5/TiO2 catalysts showed the most active DeNOx properties at low temperature. Additionally, the difference in impregnation order affected the SCR activity. The superiority of low temperature activity of the vanadium firstly added catalysts (W or Ce/V/TiO2) is attributed to the formation of more polymerized V2O5 on the sample.

Performance and Stability of the Ru–Re/γ-Al2O3 Catalyst in the Total Oxidation of Propane: Influence of the Order of Impregnation

Ru–Re/γ-Al2O3 catalysts were prepared by two sequential impregnation methods and their performances for the total oxidation of propane were investigated. TEM, XRD and H2 chemisorption data showed that the metal particle size was about 1.8 nm on both bimetallic catalysts. However, compared to the Ru/γ-Al2O3 catalyst with dispersion of 0.52, the Ru dispersion was improved by the presence of Re going from 0.64 for the catalyst with Re deposited on Ru/γ-Al2O3, to 0.70 for the sample with Ru deposited on Re/γ-Al2O3. The O2 adsorption data indicated that in the Re-modified catalysts the subsurface oxidation of Ru was suppressed, while in the Ru/γ-Al2O3 catalyst ruthenium was oxidized to a larger extent under oxidizing conditions at room temperature. The Ru deposited on Re/γ-Al2O3 exhibited a catalytic performance slightly better than the catalyst with Re impregnated on Ru/γ-Al2O3, but activity of Re-modified catalysts was not improved as compared to the Ru/γ-Al2O3 catalyst. On the other hand, bimetallic Ru–Re/γ-Al2O3 catalysts present better online stability and no deactivation was observed after the on-line tests for 30 h at temperature of 220 °C. TEM and XRD data showed that oxidized rhenium species strongly interacted with γ-alumina prevented large agglomeration of the Ru phase under O2-rich reaction conditions. The used monometallic Ru catalyst contained RuO2 oxide with crystallite size of 26 nm, while in the used bimetallic catalysts with size of 6–7 nm. Thus, in the consecutive catalytic tests Re-promoted Ru/γ-Al2O3 catalysts present higher activity and extended resistance to deactivation.

Total oxidation of propane in vanadia-promoted platinum-alumina catalysts: Influence of the order of impregnation

Differently prepared vanadium promoted Pt/alumina catalysts have been prepared, characterized and tested for propane total oxidation. V-promoted Pt/Al2O3 catalysts have shown remarkably higher catalytic activity than V-free Pt/Al2O3 catalyst. Among V-promoted Pt catalysts that prepared by coimpregnation gave the highest alkane conversions in the whole range of reaction temperatures studied. Factors such as Pt particle size or the oxidation state of platinum do not seem to be the responsible for the enhanced performance. Modification of the redox properties of the catalyst (i.e. high reducibility of vanadium species) likely provoked by the close contact between platinum particles and vanadium species and the partial introduction of vanadium in the platinum particles can be related to the improved reactivity of the PtV catalysts.