Uncalcined Catalysts Research Articles

Xanthium strumarium seed as a potential source of heterogeneous catalyst and non-edible oil for biodiesel production

A sustainable process has been developed for synthesis of biodiesel by utilizing seed shell ash and non-edible seed oil from Xanthium strumarium seeds. The catalyst prepared by open air burning (UC), calcinations at 550 °C (C550) and 700 °C (C700) was characterized by powder X-ray diffraction (XRD), fourier transform infrared (FT-IR), field emission scaning electron microscope (FESEM), energy dispersive X-ray (EDX), field emission transmission electron microscope (FETEM), X-ray photoelectron spectrometer (XPS), thermogravimetric (TG) and brunauer-emmett-teller (BET) analysis. Elemental analysis by XPS and EDX displayed the presence of potassium (34 wt%) in high concentrations that can contribute effectively to the transesterification process. The derived catalyst provides a high biodiesel yield (98.3%) at optimum operating conditions viz. 6 wt% catalyst concentrations, 9:1 methanol to oil ratio at 60 °C within 70 min. FFA content reduced from 5.63 mg in the oil to 0.28 mg in the biodiesel due to presence of considerable amount of amphoteric SiO2 and acidic P2O5 in the catalyst. The catalyst prepared at 550 °C showed the highest pH value of 11.78. The Hammett indicator test provides higher basicity for C550 (0.513 mmol/g) than that of C700 and uncalcined catalyst. The reaction follows pseudo-first-order kinetics and the activation energy was found to be 37.413 kJ mol−1. The reusability study also showed satisfactory biodiesel yield (82.3%) at 3rd round of transesterification reaction. The prepared biodiesel was characterized by 1H and 13C NMR, GC-MS analysis and the fuel parameters are evaluated by the standard protocols.

Ni-H-Beta Catalysts for Ethylene Oligomerization: Impact of Parent Cation on Ni Loading, Speciation, and Siting

Ni-H-Beta catalysts for ethylene oligomerization (EO) were prepared by ion exchange of NH4-Beta and H-Beta zeolites with aqueous Ni(NO3)2 and characterized by H2-temperature-programmed reduction (TPR), NH3-temperature-programmed desorption (TPD), and diffuse-reflectance infrared Fourier-transform spectroscopy (DRIFTS). Quadruple exchange of NH4-Beta at 70 °C resulted in 2.5 wt.% Ni loading corresponding to a Ni2+/framework aluminum (FAl) molar ratio of 0.52. [NiOH]+ and H+ are the primary charge-compensating cations in the uncalcined catalyst, as evidenced by TPR and DRIFTS. Subsequent calcination at 550 °C in air yielded a Ni-H-Beta catalyst containing primarily bare Ni2+ ions bonded to framework oxygens. Quadruple exchange of H-Beta at 70 °C gave 2.0 wt.% Ni loading (Ni2+/FAl = 0.41). After calcination at 550 °C, the resulting Ni-H-Beta catalyst comprises a mixture of bare Ni2+ ions: [NiOH]+ and NiO species. The relative abundance of [NiOH]+ increases with the number of exchanges. In situ pretreatment at 500 °C in flowing He converted the [NiOH]+ species to bare Ni2+ ions via dehydration. The bare Ni2+ ions interact strongly with the Beta framework as evidenced by a perturbed antisymmetric T-O-T vibration at 945 cm−1. DRIFT spectra of CO adsorbed at 20 °C indicate that the Ni2+ ions occupy two distinct exchange positions. The results of EO testing at 225 °C and 11 bar (ethylene) suggested that the specific Ni2+ species initially presented (e.g., bare Ni2+, [NiOH]+) did not significantly affect the catalytic performance.

The Development of Uncalcined Cu-Based Catalysts by Liquid Reduction Method for CO2 Hydrogenation to Methanol

The Development of Uncalcined Cu-Based Catalysts by Liquid Reduction Method for CO2 Hydrogenation to Methanol

Fischer-Tropsch Synthesis: The Characterization and Testing of Pt-Co/SiO2 Catalysts Prepared with Alternative Cobalt Precursors

Different low-cost cobalt precursors (acetate, chloride) and thermal treatments (air calcination/H2 reduction versus direct H2-activation) were investigated to alter the interaction between cobalt and silica. H2-activated catalysts prepared from cobalt chloride had large Co0 particles (XRD, chemisorption) formed by weak interactions between cobalt chloride and silica (temperature programmed reduction (TPR), TPR with mass spectrometry (TPR-MS), TPR with extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge spectroscopy (XANES) techniques) and retained Cl-blocked active sites, resulting in poor activity. In contrast, unpromoted Co/SiO2 catalysts derived from cobalt acetate had strong interactions between Co species and silica (TPR/TPR-MS, TPR-EXAFS/XANES); adding Pt increased the extent of the Co reduction. For these Pt-promoted catalysts, the reduction of uncalcined catalysts was faster, resulting in larger Co0 clusters (19.5 nm) in comparison with the air-calcined/H2-activated catalyst (7.8 nm). Both catalysts had CO conversions 25% higher than that of the Pt-promoted catalyst prepared in the traditional manner (air calcination/H2 reduction using cobalt nitrate) and three times higher than that of the traditional unpromoted Co/silica catalyst. The retention of residual cobalt carbide (observed in XANES) from cobalt acetate decomposition impacted performance, resulting in a higher C1–C4 selectivity (32.2% for air-calcined and 38.7% for uncalcined) than that of traditional catalysts (17.5–18.6%). The residual carbide also lowered the α-value and olefin/paraffin ratio. Future work will focus on improving selectivity through oxidation–reduction cycles.

Influence of calcination on physico-chemical properties and Ficher–Tropsch activity of titanosilicate supported cobalt catalysts with different pore sizes

Titanosilicate supports of different pore sizes were synthesized by a surfactant-free templating method. Cobalt was loaded by incipient wetness impregnation on the synthesized supports and commercial γ-Al2O3. The Fischer–Tropsch activities of the catalysts were studied with and without prior calcination in a fixed bed reactor at 220 °C, 1.83 MPa and 2000 mLsyngas/mLcatalyst/h after in situ reduction. XANES analysis of the catalysts revealed that after reduction, a greater fraction of the loaded cobalt had been reduced in the calcined catalyst (74 %) compared to the uncalcined catalyst (58 %). Activity studies revealed that the CO conversion and C5+ selectivities of the catalysts with medium pore titanosilicate supports was higher (80 % conversion, 81–85 % selectivity) than the CO conversion by Co/γ-Al2O3 (77 % conversion, 76 % selectivity). Calcination in air increased the liquid product selectivity of all the catalysts towards the diesel fraction from 21–24 % to 25–32 %.

Fischer-Tropsch synthesis: Direct cobalt nitrate reduction of promoted Co/Al2O3 catalysts

Direct reduction of cobalt nitrate versus conventional calcination/reduction treatment was conducted using alumina with identical methodology as previously applied to SiO2 and TiO2. Similar BET surface areas, pore volumes and pore size distributions were obtained for the activated calcined and uncalcined catalysts indicating no significant difference in morphological properties. However, the reducibility slightly increases and Co crystallite size is smaller for activated uncalcined samples. Reduction phenomena were analyzed by TPR-MS and TPR-EXAFS/XANES. Combining these techniques allows an explanation of the complex phenomena occurring during the direct reduction of cobalt nitrate, as both nitrate decomposition and cobalt oxide reduction are involved. Cobalt nitrate species are converted to CoOx intermediates. These species are oxidized by NOX (from nitrate decomposition) to Co3O4 spinel, which is converted to CoO prior to Co0 formation. Noble metals (Pt, Re, Ru and Ag) improve cobalt oxide reducibility, especially for the final reduction step (i.e., CoO to Co0). The effect of direct nitrate reduction on FT activity was investigated using a 1 L CSTR. Activated unpromoted and Pt-promoted uncalcined catalysts achieved higher initial and steady-state CO conversions in comparison to the corresponding calcined catalysts. The best performance was achieved with direct reduction of uncalcined 0.5 %Pt-25 %Co/Al2O3.

Fischer-Tropsch synthesis: Direct cobalt nitrate reduction of promoted Co/TiO2 catalysts

The effect of the direct reduction of cobalt nitrate versus the more conventional calcination/reduction treatment has been investigated. Porosity properties of the catalysts are not significantly modified by avoiding the calcination step, as similar BET surface area, pore volume and pore diameter are obtained for the activated catalysts. In contrast, the cobalt reducibility decreases, but smaller cobalt particles size and higher dispersion are obtained. The reduction phenomena occurring for the uncalcined catalysts are more complex because of the additional nitrate decomposition steps. TPR-MS and TPR-XANES point out that CoOx intermediate species are formed during the reductive nitrate decomposition. However, these species are oxidized by NOX (formed by nitrate decomposition) to spinel type Co3O4, which is then converted to CoO prior to the final reduction step to Co0. The addition of promoters (Pt, Re, Ru, Ag) improves the cobalt reducibility, especially by shifting the final reduction step (i.e., CoO to Co0) to lower temperature. FT activity testing data show that activated uncalcined catalysts have higher CO conversion following the initial decline and leveling off period relative to the activated calcined catalyst. The best performance is achieved with uncalcined Pt-12%Co/TiO2. This catalyst has the highest CO steady state conversion, which is 1.2 times higher than the Pt-promoted calcined catalyst. Moreover, its deactivation rate is 0.13%/h compared to 0.2%/h for the corresponding calcined catalyst. The difference in the catalytic activity is even higher for the un-promoted samples, where the activated uncalcined catalyst has almost double the CO conversion as compared to its calcined counterpart. Finally, the addition of other promoters such as Ru, Re and Ag has no significant effect on catalytic activity.

Preparation of amorphous copper - chromium oxides catalysts for selective oxidation of cyclohexane

In this work, amorphous copper-chromium catalysts with different Cu/Cr molar ratios have been prepared by a sol-gel method and were used in the oxidation of cyclohexane to KA-oil. The catalysts have been characterized by a variety of analytical techniques including XRD, XPS, Raman, FT-IR, BET, TEM and SEM. XRD results confirmed that the formation of amorphous structure. The XPS and Raman results indicated that most of Cu species existed in well-dispersed tetrahedral coordination before calcination. After calcination, the tetrahedrally coordinated Cu ions are transformed into octahedral coordination and the activity of catalyst is significantly reduced. The results show that the tetrahedrally coordinated Cu ions play the synergistic catalytic role with Cr ions. Interestingly, oxidation of cyclohexane is more inclined to produce cyclohexanol with uncalcined catalyst due to the presence of the tetrahedrally coordinated Cu ions; however, the appearance of surface lattice oxygen makes the reaction more conducive to cyclohexanone after calcination. After optimizing conditions, Cu-Cr oxide catalyst with the molar ratio 1:1 shows the highest activity, which obtains 62.2% yield and 92.4% selectivity for KA-oil using H2O2 as oxygen source.

Effect of Precursors on Morphology and Catalytic Activities of Birnessite for Methylene Blue Degradation

Manganese oxides having birnessite structure have been successfully synthesized by precipitation method. These materials were fabricated based on the reaction between KMnO4 and citric acid or oxalic acid as reductant. The precipitated solid products were heated up to 120 °C and calcined up to 600 °C. The materials were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic absorption spectroscopy (AAS), and its average oxidation state (AOS) together with the zero point charge (pHzpc) were also determined. The XRD results showed the calcined citric-prepared birnessite displayed more crystalline structure than oxalic-prepared birnessite. The SEM results indicated that the citric precursor produced aggregation particles with needle-like appearance on its crystal faces, while oxalic acid generated irregular aggregation particles. The catalytic activities of as-prepared birnessite prior to and following to calcinations were evaluated for the degradation of methylene blue (MB) with H2O2 as an oxidant. The un-calcined samples displayed much higher catalytic degradation for MB compared to calcined samples. The maximum of MB degradation obtained using un-calcined catalyst from citric acid precursor was 98%, whereas the oxalic acid was 90%. The high catalytic activity of un-calcined samples especially for citric-prepared birnessite was correlated with high defect concentration due to its low AOS Mn and small crystal size.

Cordierite honeycomb monoliths coated with Al(III)/ZrO2 as an efficient and reusable catalyst for the Knoevenagel condensation: A faster kinetics

Al(III)/ZrO2 with 5–25 wt% Al(III) was coated on honeycomb monoliths by dip & dry technique and were also prepared in their powder forms for the purpose of comparison. These prepared catalysts were characterized for their total acidity, crystallinity, and morphology. The catalytic activity of Al(III)/ZrO2 was examined in 3 different modes of heating, i.e., conventional, ultrasonic, and microwave. The effect of calcination temperature of the catalyst, poisoning of acid sites of the catalyst by adsorbing pyridine adsorption on the physico-chemical properties and the catalytic activity was also studied. The results indicated that the microwave heating mode shows highest catalytic activity when compared to either ultrasonic or conventional modes. The honeycomb form of the catalysts shows almost 1.2 fold time increase in their catalytic activity when compared to their powder forms. Pre-adsorption studies disclose that the Knoevenagel condensation reaction obeys the Langmuir-Hinshelwood type which involves chemisorptions of both of the reactants. A faster kinetic study confirms that monolithic catalysts [15Z-A (CHM)] possess the least energy of activation (35.6 kJ/mol) while their powder forms analogs [15Z-A (PFM)] posses highest activation energy (59.2 kJ/mol) correspondingly with a shorter reaction time indicating that monolithic catalysts are highly efficient compared to their powder forms. Reusability tests pertaining to both calcined and uncalcined catalysts authenticates that calcination enhances catalytic activity with the augmentation of catalytically active sites.

Esterification of high acidity vegetable oil catalyzed by tin-based catalysts with different sulfate contents: contribution of homogeneous catalysis

Biodiesel production costs can be significantly reduced by using nonrefined feedstock. Sulfated solid catalysts have been proposed for producing biodiesel from acid oils by esterification reactions. Nevertheless, leaching of sulfate species to the reaction medium may occur, but often it is not considered. In this article, a commercial tin sulfate (SnSO4) was used as a catalyst for the esterification of a feedstock with high content of free fatty acid in order to assess the contribution of the homogeneous catalysis in different situations. SnSO4 was calcined at different temperatures (300, 400, 500 and 700 °C) and converted into SnO2 after calcination at temperatures higher than 300 °C. Homogeneous catalysis seems possible to occur with all of the catalysts, but it was clearly observed for the uncalcined catalyst (SnSO4) and for that calcined at 300 °C (SnSO4(300)). For these catalysts, an important leaching of the sulfate species was confirmed. Higher conversions were obtained with the uncalcined SnSO4. Reactions at the same conditions using sulfuric acid as catalyst at concentrations of 0.1% were performed and confirmed conversions higher than 80%. Heterogeneous catalysis plays a significant role only with the catalyst that present the highest specific surface areas and acidity (SnSO4(400)). As some small amount of sulfate species is retained in the structure or surface of the calcined catalysts (even after calcination at 700 °C), we cannot exclude the possibility that these species are also leached during reaction. Thus, a possible contamination of biodiesel through the use of sulfated catalysts cannot be ruled out.

Fischer-Tropsch synthesis: Foregoing calcination and utilizing reduction promoters leads to improved conversion and selectivity with Co/silica

Foregoing calcination and utilizing direct reduction of cobalt nitrate led to the formation of smaller cobalt oxide nanoclusters in stronger interaction with silica support as intermediates of the activation process to Co° nanoparticles; this was demonstrated by TPR, TPR-MS, TPR-XANES, and TPR-EXAFS experiments using hydrogen. These intermediate cobalt oxides included a spinel (e.g., Co3O4) formed from oxidation of Co2+ species by NO2, which in turn converted to CoO prior to formation of the metal. To improve the reducibility, metal promoters such as Pt, Re, Ru, and Ag were added. Hydrogen chemisorption and EXAFS experiments revealed smaller nanoparticles; Co-Co metal coordination numbers were significantly lower for the H2-activated Co metal nanoparticles when direct reduction of the nitrate was used relative to H2-activated air calcined catalysts. Comparing at the same space velocity, the best catalysts were Re and Pt promoted 12%Co/SiO2 catalysts utilizing direct reduction of the nitrate, where initial conversions in a CSTR were up to 3.8 times higher and 71% higher than unpromoted and Pt promoted air calcined catalysts, respectively. At these conditions, methane production was lower (6.8 and 8.0% for Re and Pt promoted catalysts, respectively, by direct reduction versus 12.5 and 10.1% for unpromoted and Pt promoted air calcined catalysts) and C5+ selectivity was higher (81.2% and 81.5% for Re and Pt promoted catalysts, respectively, by direct reduction versus 73.4 and 78.8% for unpromoted and Pt promoted air calcined catalysts). The uncalcined catalysts were slightly less stable than the calcined samples, with the only exception being the rhenium promoted sample, where no visible deactivation was observed; this catalyst also had the highest catalytic activity on a per gram catalyst basis.

RuNiCo-based nanocatalysts with different nanostructures for naphthalene selective hydrogenation

The NiCo/Ni(OH)2-Co(OH)2/C bimetallic nanomaterials were prepared at room temperature (RT) via hydrazine hydrate reduction method. And the corresponding Ru/NiCo/Ni(OH)2-Co(OH)2/C (Ru-NiCo/C∼uncalcined) tri-metallic supported nanocatalysts were synthesized by galvanic replacement reaction. The multi-level supported nanostructure of ruthenium nanoclusters-on-NiCo-on-Ni(OH)2-Co(OH)2 nanoparticles (NPs) then loaded on carbon was proved by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM) and high resolution transmission electron microscope (HRTEM), high-angle annular dark-field scanning TEM (HAADF-STEM), STEM energy dispersive X-ray spectroscopy elemental mapping and line-scans (STEM-EDS), and high-sensitivity low-energy ion scattering spectroscopy (HS-LEIS) techniques. And the RuNiCo alloy/C and Ru@NiCo core-shell/C catalysts were obtained after the Ru-NiCo/C∼uncalcined catalyst annealed in hydrogen at 300 °C and 600 °C, respectively. The nanostructures of the reduced RuNiCo tri-metallic supported nanocatalysts were also characterized by the above-mentioned analysis techniques. The catalytic performance of these catalysts was evaluated by naphthalene hydrogenation. The Ru-NiCo/C∼uncalcined catalyst exhibited much more excellent catalytic performance and higher selectivity to decalin than the Ru/Ni/Ni(OH)2/C and Ru/Co/Co(OH)2/C catalysts, mainly attributed to its unique nanostructure and the positive synergistic effect among the related Ni, Co and Ru species. And Ru-NiCo/C∼uncalcined showed good stability under mild reaction conditions (reaction temperature – 60 °C and hydrogen pressure – 4.48 MPa). The effect of reaction temperature on the catalytic properties of the Ru-NiCo/C∼uncalcined catalyst was investigated in this work. However, the RuNiCo alloy/C and Ru@NiCo core-shell/C catalysts did not show any activity (yield to decalin < 0.1%) for this reaction due to their nanostructures and the absence of effective synergy effect.

Gold Nanoparticles Supported on Fe₂O₃–MO(x) (M = Al, Zr, Zn) Composite Oxides for Partial Oxidation of Methanol.

Selective production of hydrogen by partial oxidation of methanol (POM), using gold supported on composite metal oxides, Fe2O3–MO x (M: Al, Zr, Zn) was investigated. The catalysts were characterized by TGA, XRD, TEM and XPS analyses. TGA and DTGA analysis indicates that minimum decomposition temperature required to obtain α-Fe2O3 in Fe2O3–ZrO2 composite support is 570 K. The catalytic activity and stability of Au/Fe2O3 catalyst is improved by using Al2O3 as an additional support, but there is no improved activity was observed with ZrO2. The uncalcined catalysts shows high activity for selective formation of hydrogen. The presence of Al2O3 in Au/Fe2O3–Al2O3 stabilize the gold particles against sintering during calcination as evidenced from TEM analysis. XPS analysis revealed that in the uncalcined catalysts gold is present as Au2O3 and Auº. The amount of metallic gold (Auº) in the catalyst increases with increase in calcination temperature. The catalytic behavior is related to the presence of highly dispersed Au of partially oxidized state in the catalyst. Under the optimized condition, the most active catalyst Au/Fe2O3–Al2O3 shows 100% conversion and 48% H2 selectivity at 523 K. The catalytic activity of Au/Fe2O3–Al2O3 catalysts in the temperature range 423–548 K showed that methanol conversion increased with rise in temperature and attains 100% at 448 K; Hydrogen selectivity increased with rise in temperature up to 523 K and then decreased at high temperatures. The overall reactions involved are methanol combustion, partial oxidation, steam reforming and decomposition. CO produced by methanol decomposition and/or by reverse water gas shift is subsequently transformed into CO2 and H2 by the water gas shift and/or CO oxidation thereby reduce the CO selectivity. The low hydrogen selectivity at high temperature is due to reverse water gas shift and/or hydrogen combustion.

Gold nanoparticle-decorated halloysite nanotubes – Selective catalysts for benzyl alcohol oxidation

Preparation of gold nanoparticle-decorated halloysite nanotubes (Au-Hal) by a deposition method and evaluation of their catalytic activity in an oxidation of benzyl alcohol are reported. An electrostatic attraction between positively charged polyethylenimine (PEI)-capped gold nanoparticles and the negatively charged external surfaces of halloysite nanotubes (Hal nanotubes) was the key factor in fabrication of Au-Hal nanotubes. Au-Hal catalysts showed good conversions and surprisingly high benzaldehyde selectivities (above 90%) in the benzyl alcohol oxidation. Influence of the amount of PEI used as a capping agent, the gold content and calcination of Au-Hal catalysts on the conversion and selectivity was investigated. A notable increase in the benzaldehyde selectivity at higher PEI contents and a significant drop in the benzaldehyde selectivity on calcination clearly indicate the central role of PEI in the selective formation of benzaldehyde. The high benzaldehyde selectivity of uncalcined catalysts are probably due to PEI donor molecules coordinating to certain surface sites on Au nanoparticles and thus blocking the catalytic sites required for further oxidation of benzaldehyde to benzoic acid. The high combined selectivity of benzoic acid and benzyl benzoate obtained with the calcined catalysts indicates that naked gold nanoparticles have the catalytic sites available for the benzoic acid formation.

Hydrogen Production by Partial Oxidation of Methanol Over Gold Supported on Fe&lt;SUB&gt;2&lt;/SUB&gt;O&lt;SUB&gt;3&lt;/SUB&gt;

Partial oxidation of methanol (POM) to produce hydrogen was investigated over Au/Fe2O3 catalysts. The catalysts were prepared by inverse co-precipitation method. The influence of catalyst synthesis parameters such as precipitant, gold loading, calcination temperature and reaction parameter such as reaction temperature on POM reaction to produce hydrogen were investigated. The catalysts have been characterized by means of TGA, BET, XRD, TEM, SEM-EDS and XPS analyses. TGA and DTGA profiles clearly indicate that minimum decomposition temperature required to obtain Fe2O3 in Au/Fe2O3 catalysts is 660 K. SEM-EDS analysis confirms that Au and Fe in Au/Fe2O3 are homogeneously distributed over the agglomerate. A detailed microstuctural characterization of Au/Fe2O3 sample by XRD, TEM and XPS analyses has shown that nanometer sized gold particles with oxidized gold species is in predominant amount in the uncalcined catalysts sample. The mean particle size and metallic state of gold particles increase with increasing calcination temperature. A highly active Au/Fe2O3 catalyst is obtained by using Na2CO3 as precipitant with lower gold loading and calcination at 673 K. The catalytic behavior of the Au/Fe2O3 catalyst is related not only to the gold but also to the chemical state of the support. The effect of reaction temperature on the catalytic performance of the Au/Fe2O3 catalysts was studied in the temperature range of 423 to 523 K. Oxygen conversion was complete through out the examined temperature range. Methanol conversion increased with rise in temperature and attains 100% at 503 K; Hydrogen selectivity increased with rise in reaction temperature up to 523 K and then dropped off. The overall reactions involved are methanol combustion, partial oxidation, steam reforming and decomposition. CO produced by methanol decomposition and/or by reverse water gas shift is subsequently transformed into CO2 and H2 by the water gas shift and/or CO oxidation.

The effect of the amount of ammonia on the Cu0/Cu+ ratio of Cu/SiO2 catalyst for the hydrogenation of dimethyl oxalate to ethylene glycol

Abstract The effect of the amount of precipitant ammonia on the Cu0/Cu+ ratio of Cu/SiO2 prepared by the deposition–precipitation method is investigated. Species at different preparation stages, resulted from the amount of ammonia used, are identified by the XRD and FTIR techniques. Chrysocolla together with either copper nitrate hydroxide or copper hydroxide coexist in the uncalcined catalysts. Upon calcination, the latter two species are converted to CuO particles while chrysocolla remains. Following reduction, CuO is transformed to metallic Cu and chrysocolla is converted to Cu2O. The value of Cu0/Cu+ ratio can be evaluated using the peak areas in their TPR profiles. Hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG) shows that the selectivity of EG depends on the Cu0/Cu+ ratio. Catalyst prepared with the addition of ammonia solution at n(NH3)/n(Cu2+) = 0.9 for precipitation–deposition gains a more suitable Cu0/Cu+ ratio upon reduction and thus has a higher selectivity for EG.

Effect of modifiers on the performance of Cu-ZnO-based catalysts for low-temperature methanol synthesis

A series of Cu-ZnO-based catalysts modified with Al, Zr, and Ce for the low-temperature methanol synthesis were prepared through co-precipitation and characterized by N2 sorption, H2-TPR, CO2-TPD, N2O titration, XRD, and high-resolution TEM; the effect of various modifiers and calcination temperature on their catalytic performance in methanol synthesis at 170°C was investigated. The results showed that the Cu-ZnO-based catalyst modified with ZrO2, among the various modifiers, exhibits the highest activity. Meanwhile, a lower calcination temperature is propitious to get a higher Cu dispersion, a smaller Cu crystal size, and a higher low temperature activity for methanol synthesis; as a result, the uncalcined catalyst exhibits excellent catalytic performance, with a productivity of 106.02 g/(kg·h) and a selectivity of 87.04% to methanol.

Preparation of Highly Active Alumina-Pillared Clay Montmorillonite-Supported Platinum Catalyst for Hydrodesulfurization

Effect of Pt precursor and pretreatment on hydrodesulfurization (HDS) activity of Pt/Al-PILM catalyst was examined to prepare highly active Pt-supported HDS catalyst. The order of HDS activities of Pt/alumina-pillared clay montmorillonite (Al-PILM) catalysts prepared by various Pt precursors was Pt(C5H7O2)2 > H2PtCl6 · 6H2O > [Pt(NH3)4](NO3)2 > [Pt(NH3)4]Cl2 · H2O > H2Pt(OH)6. This order was in accordance with that of Pt dispersion. Thus, high Pt dispersion is essential factor to prepare highly active Pt/Al-PILM catalyst for HDS reaction. On the other hand, the effect of pretreatment on the HDS activities of Pt/Al-PILM catalysts prepared by various Pt precursors was also evaluated. The UC-TPS Pt/Al-PILM catalyst showed the highest HDS activity among various pretreated Pt/Al-PILM catalysts, in which uncalcined catalyst was sulfided by temperature programmed sulfidation (TPS). We assumed that high HDS activity of UC-TPS Pt/Al-PILM catalyst is caused by partly sulfided Pt particle with high dispersion. It is concluded that the highly active Pt/Al-PILM catalyst for the HDS reaction could be prepared by using Pt(C5H7O2)2 as a precursor and UC-TPS treatment.

The interaction of cobalt species with alumina on Co/Al 2O 3 catalysts prepared by atomic layer deposition

Alumina supported cobalt catalysts were prepared by atomic layer deposition (ALD) of cobalt acetylacetonate precursors (Co(acac) 2 and Co(acac) 3). The main modes of interaction between the acetylacetonate precursors and the support were found to be the exchange reaction between the alumina OH-groups and the acac-ligands of the precursor and dissociative adsorption on coordinatively unsaturated Al 3+ sites. The amount of precursor that could adsorb on the support was determined by steric hindrance. Samples were prepared using 1–5 reaction cycles, i.e. subsequent precursor addition (Co(acac) 2) and calcination, resulting in catalysts containing ca. 3–10 wt.% Co. Samples were also prepared where the last calcination step was omitted, i.e. uncalcined catalysts. Calcination at 450 °C decreased the reducibility of the Co(acac) 2/Al 2O 3 catalysts due to formation of a cobalt oxide phase strongly interacting with the support and aluminate type surface species. The reducibility increased with metal loading on both calcined and uncalcined catalysts; however the reducibility of the calcined catalysts remained lower than of the uncalcined ones. The dispersion was found to be lower on the calcined catalysts. The cobalt particle sizes on the calcined samples was ca. 8 nm and on the uncalcined 4–5 nm, for cobalt loadings of ca. 6–10 wt.%. Catalytic activity was tested by gas phase hydrogenation of toluene in temperature programmed mode (30–150 °C).