Effects of Co dopants and flame conditions on the formation of Co/ZrO2 nanoparticles by flame spray pyrolysis and their catalytic properties in CO hydrogenation

The Co/ZrO₂ catalysts with various Co loadings (5–10 wt.%) were prepared by one-step flame spray pyrolysis (FSP) under different flame conditions. As revealed by XRD and TEM, all the resulting Co/ZrO₂ nanoparticles were composed of single-crystalline particles exhibiting the characteristic tetragonal structure of ZrO₂. Varying the amount of Co dopants during FSP synthesis did not alter the primary particle size of ZrO₂ which was determined to be ca. 14 nm. On the other hand, increasing precursor feed rate from 3 to 8 ml/min resulted in an increase of ZrO₂ crystallite size from 10 to 19 nm. The higher precursor feed rate produced higher enthalpy of flame and longer residence times, which increased coalescence and sintering of the particles. Compared to the Co/ZrO₂ prepared by conventional impregnation method, the catalytic activities of the FSP-made catalysts were much higher. Moreover, the hydrogenation rates of the FSP-made Co/ZrO₂ catalysts were increased with increasing Co loading and precursor feed rate. According to H₂ chemisorption and H₂ temperature program reduction results, the improvement of catalytic activity and C₂–C₆ selectivities of the FSP-made catalysts in the CO hydrogenation was attributed to the higher number of Co metal active sites and lower interaction between Co/CoO and ZrO₂ support obtained via the FSP synthesis.     

Selective Hydrogenation of Cinnamaldehyde over Pt/ZrO2 Catalyst Modified by Cr, Mn, Fe, Co and Ni

Hydrogenation properties of cinnamaldehyde (CMA) have been studied over Pt/ZrO₂ and PtM/ZrO₂ catalysts (M = Cr, Mn, Fe, Co and Ni) in ethanol at 343 K and 2.0 MPa. The effect of different content of Ni and base has also been investigated over PtNi/ZrO₂ catalyst. With introduction of transition metals to Pt/ZrO₂ catalyst shows a significant influence on the catalytic properties. PtCo/ZrO₂ catalysts show the best yield of cinnamyl alcohol (CMO), and PtNi/ZrO₂ catalyst shows good yield of hydrocinnamaldehyde (HCMA). In the presence of base solution, rate of the hydrogenation of CMA over PtNi/ZrO₂(0.4 wt%) catalyst increases significantly and side reaction is remarkably inhibited. More bare metal atoms situated remote from the interface region on PtNi/ZrO₂ catalyst surface are the reason of good selectivity of HCMA for PtNi/ZrO₂ catalyst.     

Enhancing the Fischer–Tropsch Synthesis Activity of Co-based Catalysts by Adding ZrOx to the SiO2 Support and Chelating Ligands to the Co-precursor

Abstract  

Co/ZrO _x /SiO₂ catalysts with enhanced dispersion of Co⁰ and turnover frequency were successfully prepared combining two different promotion effects, i.e., modifications of SiO₂ surface with ZrO _x by liquid phase deposition and influencing coordination structure of Co species using chelating agents or glycols. The catalysts exhibited ~6.3-fold higher CO conversion than Co/SiO₂ and those promoted by organic additives or ZrO _x alone, indicating activity enhancement was induced by cooperation of these two promoters.     

A contrastive study of the introduction of cobalt as a modifier for active components and supports of catalysts for NH3-SCR

Three catalysts Mn/Ce–ZrO_X, Mn–Co/Ce–ZrO_X and Mn/Co–Ce–ZrO_X were used for low-temperature NH₃-SCR of NO. XRD, TPR and XPS were performed to characterize the physicochemical property of the catalysts. Experimental results showed that Mn/Co–Ce–ZrO_X had a higher dispersion of manganese oxides, a better redox property, more surface acid sites and more surface adsorbed oxygen species and Mn⁴⁺ ion. These facts caused a better low-temperature activity for Mn/Co–Ce–ZrO_X which was 99.0% at 180 °C. Furthermore, Mn/Co–Ce–ZrO_X showed the best resistance to SO₂ and H₂O which mainly because the introduction of cobalt inhibited the formation of sulfate salts and hydroxyls on the surface of Mn/Co–Ce–ZrO_X.     

The Effect of Surface Acidic and Basic Properties on the Performance of Cobalt-Based Catalysts for Ethanol Steam Reforming

In this study, the effect of surface acidic and basic properties of y-Al₂O₃-, ZrO₂-, and CeO₂-supported cobalt catalysts on their catalytic performance during ethanol steam reforming was investigated using various characterization techniques including temperature programmed desorption, CO₂ and NH₃ pulse chemisorption, and diffuse reflectance infrared fourier transform spectroscopy. The steady-state reaction experiments showed that catalyst exhibited decreasing performance (i.e., less activity and worse stability) by following the order of Co/CeO₂?>?Co/ZrO₂?>?Co/Al₂O₃. Characterization results showed the catalysts had the reverse order of surface acidity (i.e., Co/CeO₂?<?Co/ZrO₂?<?Co/Al₂O₃), indicating that the performance difference could be attributed to the variation of surface acidic and basic properties in addition to the oxygen mobility variations reported previously.     

Selective Production of C4 Hydrocarbons from Syngas Using Fe‐Co/ZrO2 and SO42—/ZrO2 Catalysts

Modified Fischer‐Tropsch (MFT) syntheses were carried out to convert synthesis gas to C₄ hydrocarbons over Fe‐Co/ZrO₂ (FT) and SO₄^2—/ZrO₂ (SZ) catalysts in a dual reactor system, keeping the FT to SZ catalysts ratio at 1:1.5. Five Fe‐Co/ZrO₂ catalysts with different Fe and Co loading, and SZ with 15 wt% SO₄^2— were prepared and extensively characterized using various physico‐chemical methods. The FT synthesis process was initially performed using a Fe‐Co/ZrO₂ catalyst in a single reactor and the effects of Fe and Co mass ratio, reaction temperature, space velocity on the production of C₄ hydrocarbons and C₂‐C₄ olefins were investigated. Results indicated that a 3.71% Fe—8.76% Co/ZrO₂ mixed oxide catalyst alone at 260°C and 5 h^—1 gave high selectivities of C₂‐C₄ olefins (～26.1 wt%) and total C₄ hydrocarbon product (～16.2 wt%). The MFT process 150°C gave higher C₄ (～31.6 wt%), isobutane (～22.9 wt%) and C₂‐C₄ (31.1 wt%) selectivities.     

Synthesis of highly active superacids of SO4/ZrO2 with Ir,Pt, Rh,Ru, Os,and Pd substances for reaction of butane

Highly acidic catalysts stronger than the SO₄/ZrO₂ superacid with an acid strength of Ho –16.04 were obtained by kneading Zr(OH)₄ with ammonium sulfate together with chlorides of Ir, Pt, Rh, Ru, Os, and Pd followed by calcining in air at 600°C, the metal concentration being equivalent to Pt of 7.5 wt% based on the hydroxide. The catalysts with Ir and Pt materials were highest in activity for the skeletal isomerization of butane to isobutane. The present catalysts were not obtained by treating the crystallized oxide, ZrO₂ calcined at 700°C, but the amorphous form followed by calcination to the crystallization.Superacids by metal oxides, VI. For previous publication in this series see ref. [1].     

ZrC–C and ZrO2–C as Novel Supports of Pd Catalysts for Formic Acid Electrooxidation

The Pd/ZrC–C and Pd/ZrO₂–C catalysts with zirconium compounds ZrC or ZrO₂ and carbon hybrids as novel supports for direct formic acid fuel cell (DFAFC) have been synthesized by microwave‐assisted polyol process. The Pd/ZrC–C and Pd/ZrO₂–C catalysts have been characterized by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), energy dispersive analysis of X‐ray (EDAX), transmission electron microscopy (TEM), and electrochemical measurements. The physical characteristics present that the zirconium compounds ZrC and ZrO₂ may promote the dispersion of Pd nanoparticles. The results of electrochemical tests show that the activity and stability of Pd/ZrC–C and Pd/ZrO₂–C catalysts show higher than that of Pd/C catalyst for formic acid electrooxidation due to anti‐corrosion property of zirconium compounds ZrC, ZrO₂, and metal–support interaction between Pd nanoparticles and ZrC, ZrO₂. The Pd/ZrC–C catalyst displays the best performance among the three catalysts. The peak current density of formic acid electrooxidation on Pd/ZrC–C electrode is nearly 1.63 times of that on Pd/C. The optimal mass ratio of ZrC to XC‐72 carbon is 1:1 in Pd/ZrC–C catalyst with narrower particle size distribution and better dispersion on surface of the mixture support, which exhibits the best activity and stability for formic acid electrooxidation among all the samples.     

New Catalysts for the Hydrogenation of Glucose to Sorbitol

Nickel catalysts supported on ZrO₂, TiO₂ and ZrO₂/TiO₂ mixtures performed more active, selective and stable than Ni/SiO₂ catalysts in the hydrogenation of glucose to sorbitol. This was shown by catalytic testing as well as by determination of Ni crystallite size before and after the test. The reason for the better performance was assumed to be metal‐support interaction in the Ni/ZrO₂, Ni/TiO₂ and Ni/ZrO₂/TiO₂ catalysts.     

Reaction performance and characterization of Co/Al2O3 Fischer–Tropsch catalysts promoted with Pt, Pd and Ru

A series of noble metal (Pt, Ru or Pd) promoted Co/Al₂O₃ catalysts were prepared by sequential impregnation method. The catalysts were characterized by XRD, TPR, H₂-TPD and TPSR techniques, and their catalytic performance in Fischer–Tropsch synthesis was investigated in a fixed-bed reactor. The results of activity measurements show that the addition of small amounts of noble metal greatly improved the activity of the Co/Al₂O₃ catalyst. TPR experimental results demonstrate that hydrogen spillover from the noble metal to cobalt oxide clusters facilitated the reduction of cobalt oxide and, thus significantly increased the reducibility of Co/Al₂O₃ catalyst. The presence of noble metal increased the amount of chemisorbed hydrogen and weakened the bond strength of Co–H. TPSR results indicate that CO was adsorbed in a more reactive state on the promoted catalysts.     

Silica Gel-Supported, Metal-Promoted MoS2 Catalysts for HDS Reactions

Silica-supported, metal-promoted MoS₂ catalysts were prepared. Sol–gel method was used for providing the SiO₂ support as well as for including the catalyst precursors and promoter in one single step of preparation. The general idea in this approach is to obtain the promoted MoS₂ catalyst phase finely and uniformly distributed in the SiO₂ support. Scanning electron microscopy of the obtained catalysts shows a fine and homogeneous distribution of the metal-promoted MoS₂ particles on the SiO₂ matrix with surface area between 62 and 104m²/g. Metal promoter affects the surface area, pore size distribution and the hydrodesulfurization (HDS) activity and selectivity. When different promoters were used at the same amount, the highest selectivity for direct C–S bound cleavage is observed for Ru/MoS₂/SiO₂ catalyst, and at different amounts of Co the highest selectivity was occurred with Co/MoS₂/SiO₂ at 12% of Co/MoS₂, X-ray diffraction studies showed that the catalysts are poorly crystallized with a very weak intensity of the (002) line of 2H-MoS₂. Comparison on the catalytic activities of the catalysts with different metal promoters was made. Catalytic activity results showed the method of preparation used in this study is successful in producing very efficient catalysts for the HDS of dibenzothiophene (DBT). Silica-supported, cobalt-promoted MoS₂ catalyst showed the highest activity.     

Hydrogen Production from Ethanol Steam Reforming Over Supported Cobalt Catalysts

Hydrogen production was carried out via ethanol steam reforming over supported cobalt catalysts. Wet incipient impregnation method was used to support cobalt on ZrO₂, CeO₂ and CeZrO₄ followed by pre-reduction with H₂ up to 677 °C to attain supported cobalt catalysts. It was found that the non-noble metal based 10 wt.% Co/CeZrO₄ is an efficient catalyst to achieve ethanol conversion of 100% and hydrogen yield of 82% (4.9 mol H₂/mol ethanol) at 450 °C, which is superior to 0.5 wt.% Rh/Al₂O₃. The pre-reduction process is required to activate supported cobalt catalysts for high H₂ yield of ethanol steam reforming. In addition, support effect is found significant for cobalt during ethanol steam reforming. 10% Co/CeO₂ gave high H₂ selectivity while suffered low conversion due to the poor thermal stability. In contrast to CeO₂, 10 wt.% Co/ZrO₂ achieved high conversion while suffered lower H₂ yield due to the production of methane. The synergistic effect of ZrO₂ and CeO₂ to promote high ethanol conversion while suppress methanation was observed when CeZrO₄ was used as a support for cobalt. This synergistic effect of CeZrO₄ support leads to a high hydrogen yield at low temperature for 10 wt.% Co/CeZrO₄ catalyst. Under the high weight hourly space velocity (WHSV) of ethanol (2.5 h⁻¹), the hydrogen yield over 10 wt.% Co/CeZrO₄ was found to gradually decrease to 70% of its initial value in 6 h possibly due to the coke formation on the catalyst.     

Steam reforming of ethanol on Ni–CeO2–ZrO2 catalysts: Effect of doping with copper, cobalt and calcium

Steam reforming (SR) and oxidative steam reforming (OSR) of ethanol were investigated over undoped and Cu, Co and Ca doped Ni/CeO₂–ZrO₂ catalyst in the temperature range of 400–650 °C. The nickel loading was kept fixed at 30 wt.% and the loading of Cu and Co was varied from 2 to 10 wt% whereas the Ca loading was varied from 5 to 15 wt.%. The catalysts were characterized by various techniques, such as surface area, temperature programmed reduction, X-Ray diffraction and H₂ chemisorption. For Cu and Co doped catalyst, CuO and Co₃O₄ phases were detected at high loading whereas for Ca doped catalyst, no separate phase of CaO was found. The reducibility and the metal support interactions were different for doped catalysts and varied with the amount and nature of dopants. The hydrogen uptake, nickel dispersion and nickel surface area was reduced with the metal loading and for the Co loaded catalysts the dispersion of Ni and nickel surface area was very low. For Cu and Ca doped catalysts, the activity was increased significantly and the main products were H₂, CO, CH₄ and CO₂. However, the Co doped catalysts showed poor activity and a relatively large amount of C₂H₄, C₂H₆, CH₃CHO and CH₃COCH₃ were obtained. For SR, the maximum enhancement in catalytic activity was obtained with in the order of NCu5. For Cu–Ni catalysts, CH₃CHO decomposition and reforming reaction was faster than ethanol dehydrogenation reaction. Addition of Cu and Ca enhanced the water gas shift (WGS) and acetaldehyde reforming reactions, as a result the selectivity to CO₂ and H₂ were increased and the selectivity to CH₃CHO was reduced significantly. The maximum hydrogen selectivity was obtained for Catalyst N (93.4%) at 650 °C whereas nearly the same selectivity to hydrogen (89%) was obtained for NCa10 catalyst at 550 °C. In OSR, the catalytic activity was in the order N > NCu5 > NCa15 > NCo5. In the presence of oxygen, oxidation of ethanol was appreciable together with ethanol dehydrogenation. For SR reaction, the highest hydrogen yield was obtained on the undoped catalyst at 600 °C. However, with calcium doping the hydrogen yields are higher than the undoped catalyst in the temperature range of 400–550 °C.     

Characterization of Cobalt Dispersed on Various Micro- and Nanoscale Silica and Zirconia Supports

Cobalt dispersion on various micro- and nanoscale SiO₂ and ZrO₂ was investigated. It revealed that Co/SiO₂ (M) exhibited higher activity than Co/SiO₂ (N) due to strong support interaction. However, Co/ZrO₂ behaved oppositely. In addition, Co dispersed on the nanoscale SiO₂ and ZrO₂ gave the similar activity for CO hydrogenation because of more uniform species.     

Influences of preparation methods of ZrO2 support and treatment conditions of Cu/ZrO2 catalysts on synthesis of methanol via CO hydrogenation

ZrO₂ supports were prepared by different methods (conventional precipitation method, shortened as “CP”, and alcogel/thermal treated with nitrogen method, shortened as “AN”), and Cu/ZrO₂ catalysts were prepared by impregnation method. The supports and catalysts were characterized by BET, XRD, TEM and TPR. The effects of the preparation methods of ZrO₂ supports and the treatment conditions (calcination and reduction temperatures) of the catalyst precursors on the texture structures of the supports and catalysts as well as on the catalytic performances of Cu/ZrO₂ in CO hydrogenation were investigated. The results showed that the support ZrO₂-AN had larger BET specific surface area, cumulative pore volume and average pore size than the support ZrO₂-CP. Cu/ZrO₂-AN catalysts showed higher CO hydrogenation activity and selectivity of oxygenates (C₁–C₄ alcohols and dimethyl ether) than Cu/ZrO₂-CP catalysts. Calcination and reduction temperatures of supports and catalyst precursors affected the catalytic performance of Cu/ZrO₂. The conversion of CO and the STY of oxygenates were 12.7% and 229 g/kg h, respectively, over Cu/ZrO₂-AN-550 at the conditions of 300 °C, 6 MPa.     

Suppression of carbon formation in steam reforming of methane by addition of Co into Ni/ZrO2 catalysts

We investigated the steam reforming of methane (SRM) over various NiCo bimetallic catalysts supported on ZrO₂ to determine whether the addition of Co on the Ni catalyst suppressed carbon formation. The effect of metal loading on SRM reaction was evaluated in a downflow tubular fixed-bed reactor under various steam-to-carbon (S/C) ratios and temperatures. For monitoring changes in the catalysts before and after the SRM reactions, several techniques (BET, XRD, TEM, and CHN analysis) were used. The effects of reaction temperature, gas hourly space velocity (GHSV), and molar S/C ratios were studied in detail over the various catalyst combinations. It was found that an Ni- to-Co ratio of 50: 50 supported on ZrO₂ provided the best catalytic activity, along with an absence of coking, when operated at a temperature of 1,073 K, a GHSV of 24 L g⁻¹ h⁻¹, and an S/C ratio of 3: 1.     

Catalytic Methanation of Carbon Dioxide by Active Oxygen Material CexZr1−xO2 Supported Ni?Co Bimetallic Nanocatalysts

A series of active oxygen material Ce_xZr_1?xO₂‐supported Ni? Co bimetallic nanosized catalysts were prepared by coprecipitation method, which is simple and fit for industrial use with lower cost than other methods. The effect of CeO₂/ZrO₂ mole ratio, Co metal addition, and PEG‐6000 addition were investigated. The catalysts were characterized through X‐ray diffraction, H₂ thermal‐programmed reduction, N₂ adsorption, Raman spectroscopy, CO pulse chemisorption, X‐ray photoelectron spectroscopy, oxygen storage capacity, and transmission electron microscopy‐energy dispersive X‐ray analysis. Modifications of the structural and redox properties of these materials were evaluated in relation to their catalytic performances. Particularly, the relationship between the active oxygen sites of the catalysts and their catalytic performances was investigated. The interaction between active metals (Ni and Co) and Ce_xZr_1?xO₂ support was found to be very important for catalytic performance. The active oxygen site of Ce_xZr_1?xO₂ can considerably improve catalytic performance. Appropriate Co metal addition also remarkably enhanced the catalytic stability and activity. Moreover, PEG‐6000 addition can improve the Brunauer–Emmett–Teller surface area and active metal dispersion of catalysts to improve their performances. The nanosized catalyst 15 wt % Ni‐5 wt % Co/Ce_0.25Zr_0.75O₂ prepared by adding 5 wt % PEG‐6000 achieved almost 85% CO₂ conversion and 98% selectivity to methane at 280°C when the gas hourly space velocity was 10,000 h^?1. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2567–2576, 2013     

Selective CO oxidation in the presence of hydrogen over supported Pt catalysts promoted with transition metals

Selective CO oxidation in the presence of excess hydrogen was studied over supported Pt catalysts promoted with various transition metal compounds such as Cr, Mn, Fe, Co, Ni, Cu, Zn, and Zr. CO chemisorption, XRD, TPR, and TPO were conducted to characterize active catalysts. Among them, Pt-Ni/γ-Al₂O₃ showed high CO conversions over wide reaction temperatures. For supported Pt-Ni catalysts, Alumina was superior to TiO₂ and ZrO₂ as a support. The catalytic activity at low temperatures increased with increasing the molar ratio of Ni/Pt. This accompanied the TPR peak shift to lower temperatures. The optimum molar ratio between Ni and Pt was determined to be 5. This Pt-Ni/γ A1₂O₃ showed no decrease in CO conversion and CO₂ selectivity for the selective CO oxidation in the presence of 2 vol% H₂O and 20 vol% CO₂. The bimetallic phase of Pt-Ni seems to give rise to stable activity with high CO₂ selectivity in selective oxidation of CO in H₂-rich stream.     

Mesoporous molecular sieve MCM-41 supported Co–Mo catalyst for hydrodesulfurization of dibenzothiophene in distillate fuels

A mesoporous aluminosilicate molecular sieve with MCM-41 type structure was synthesized using aluminum isopropoxide as the Al source. Supported Co–Mo/MCM-41 catalysts were prepared by co-impregnation of Co(NO₃)₂·6H₂O and (NH₄)₆Mo₇O₂₄ followed by calcination and sulfidation. For comparison, conventional Al₂O₃-supported sulfided Co–Mo catalysts were also prepared using the same procedure. These two types of catalysts were examined at two different metal loading levels in hydrodesulfurization of a model fuel containing 3.5 wt% sulfur as dibenzothiophene in n-tridecane. At 350–375°C under higher H₂ pressure (6.9 MPa), sulfided Co–Mo/MCM-41 catalysts show higher hydrogenation and hydrocracking activities at both normal and high metal loading levels, whereas Co–Mo/Al₂O₃ catalysts show higher selectivity to desulfurization. Co–Mo/MCM-41 catalyst at high metal loading level is substantially more active than the Co–Mo/Al₂O₃ catalysts.     

SELECTIVE CARBON MONOXIDE OXIDATION IN H2-RICH GAS STREAM OVER Co3O4/CeO2/ZrO2, Ag/CeO2/ZrO2, AND MnO2/CeO2/ZrO2 CATALYSTS

Activity and selectivity of selective CO oxidation in an H₂-rich gas stream over Co₃O₄/CeO₂/ZrO₂, Ag/CeO₂/ZrO₂, and MnO₂/CeO₂/ZrO₂ catalysts were studied. Effects of the metaloxide types and metaloxide molar ratios were investigated. XRD, SEM, and N₂ physisorption techniques were used to characterize the catalysts. All catalysts showed mesoporous structure. The best activity was obtained from 80/10/10 Co₃O₄/CeO₂/ZrO₂ catalyst, which resulted in 90% CO conversion at 200°C and selectivity greater than 80% at 125°C. Activity of the Co₃O₄/CeO₂/ZrO₂ catalyst increased with increase in Co₃O₄ molar ratio.