Physicochemical properties of pine-derived bio-chars modified by metal oxides and their performance in the removal of NO

Pine-derived bio-chars have been prepared at different temperatures with and without KOH chemical activation. Three metal oxides (V₂O₅, MnO and CuO) were loaded on this chars by incipient-wetness impregnation method respectively. Pine wood pellets were characterized by thermogravimetric, and pine-chars samples were characterized by SEM-EDS, XRD, N₂ physisorption and FTIR. Activity test for the selective catalytic reduction of NO with NH₃ was also carried out in dry simulated flue gas at fixed temperature 160 °C. The results show that pretreatment with KOH and carbonization at 600 °C seems to be the best method for pine-chars preparation. Active metal oxides are well distributed on the surface of carbon support and are partly reduced by carbon during preparation. The mesopores disappear in V- and Mn-containing samples, and V-addition could decrease the amount of micropores as well. At the fixed temperature 160 °C, the active metal oxides have an order of CuO > V₂O₅ >> MnO_x >> Non-modified sample on the NO reduction activity. Pine-chars modified by CuO seems to be the best option in this research.     

Synthesis of highly active and stable Pd/C catalysts toward HCOOH dehydrogenation by a simple NH3 adsorption method

Pd catalysts supported on activated carbon (Pd/C–NH₃) toward HCOOH dehydrogenation were prepared by a simple adsorption method using ammonia (NH₃) and Ar as the working gas. The results show that the TOF_initial of Pd/C–NH₃ was 459.8 h⁻¹ at 50 °C. When the reaction was carried out for 4 h, the HCOOH dehydrogenation ratio over Pd/C–NH₃ was about 81.2%, which was 1.15 and 1.13 times, respectively, as that of the as-prepared Pd/C catalyst without any treatment (Pd/C–As) and the Pd/C catalyst purchased from Sigma-Aldrich (Pd/C-CM). The total amount of H₂ and CO₂ produced by using Pd/C–NH₃ to decompose HCOOH in the third cycle was 99.4% of the gas produced by the first reaction cycle, and 1.80 and 12.60 times, respectively, as that of Pd/C–As and Pd/C-CM. The characterization results indicated that the Pd active species in Pd/C–NH₃ migrated to the outer surface of the carbon support during the reaction, and the pore volume of the carbon support became larger, which were beneficial to the reaction. These factors made Pd/C–NH₃ exhibit excellent HCOOH dehydrogenation activity and stability. NH₃ adsorption is a simple and effective method for preparing high-performance Pd/C HCOOH dehydrogenation catalysts, and has important guiding significance for the preparation of other carbon supported noble metal catalysts.     

Methanation of CO on Ru/graphitized-carbon catalysts: Effects of the preparation method and the carbon support structure

Two kinds of Ru/C catalysts prepared by two different methods and supported on two graphitized carbons differing in their surface area were studied in CO methanation in the H₂-rich gas. The textural parameters of the support materials were characterized by means of N₂ physisorption. XRPD, XPS, TEM and CO- chemisorption studies indicate that the application of wet impregnation leads to more homogeneous composition of the Ru/carbon system and higher Ru dispersion than dry impregnation for both supports. The activity of the Ru/carbon samples in CO methanation in a H₂-rich gas stream depends on the structure and average size of the active phase crystallites. The combination of wet impregnation and the use of graphitized carbon of appropriate structure in the preparation of the Ru/C catalyst lead to a complete conversion of CO at 240 °C.     

Catalytic dehydrogenation study of dodecahydro-N-ethylcarbazole by noble metal supported on reduced graphene oxide

Through systematical experiments, a comparative study was conducted concerning several graphene-supported noble metal catalysts for dehydrogenation of dodecahydro-N-ethylcarbazole (12H-NEC). It was found that the catalytic activity of the prepared graphene-supported noble metal catalysts was following the order of Pd > Pt > Rh > Ru > Au for the dehydrogenation process. Pd supported on reduced graphene oxide (rGO) prepared by one-pot in situ synthesis has much more excellent catalytic performance than other kinds of catalysts investigated for comparison, simultaneously the using amount of noble metals can obviously be decreased. To be specific, at 453 K, the final dehydrogenation product catalyzed by the novel catalyst of Pd/rGO is N-ethylcarbazole (NEC) and the process selectivity was increased from 44.77% (commercial Pd/Al₂O₃) to 97.65%, as well as the dehydrogenation ratio reached 99.14%. In addition, the novel catalyst is also superior to other reported catalysts in terms of dehydrogenation performance of 12H-NEC. Its dehydrogenation activity at 443 and 433 K of Pd/rGO was tested and the catalytic performance keeps stable at the two temperatures. Based on the experimental data, kinetic calculation was carried out and some fundamental parameters regarding reaction kinetics was obtained.     

Activities of Pt/Sibunit-1562 catalysts in the ORR in PEMFC: Effect of Pt content and Pt load at cathode

In this paper, a systematic investigation was carried out of activities at 80 °C of Pt supported on Sibunit-1562 graphitized carbon in the electroreduction of oxygen in the polymer electrolyte fuel cell. Pt content in the Pt/Sibunit-1562 catalysts was 20, 40, and 60 wt.% and Pt load at the cathode was varied in the 200–6.25 μg_Pt cm⁻² interval. The results were compared with the activity of commercial 20 wt.% Pt/Vulcan XC-72 catalyst. To optimize the transport properties of the cathode layer and maintain its thickness upon using Pt/Sibunit −1562 catalysts with varied Pt content and Pt loads a definite amount of Vulcan-XC-72 carbon support was added to the cathode catalytic inks. Higher activity of Pt/Sibunit-1562 catalysts was found as compared to that of commercial 20 wt.% Pt/Vulcan XC-72 with similar particle size of the active component.     

Hydrogen production from oxidative steam reforming of ethanol over Ir catalysts supported on Ce–La solid solution

The Ce_1?xLa_xO_2?δ solid solution (CL) supported Ir (nIr/CL, n = 2, 5 and 10 wt.%) catalysts are studied for H₂ production from ethanol oxidative steam reforming (OSR). The Ir dispersion, surface area, oxygen vacancy density and carbon deposition resistance of nIr/CL catalysts are greatly enhanced compared with Ir/CeO₂. Among the tested catalysts, 5%Ir/CL shows the best catalytic performance, exhibiting >99.9% ethanol conversion at 400 °C with H₂ yield rate of 323 μmol·g_cata^?1·s^?1 and no obvious carbon deposition after used. The 5%Ir/CL catalyst contains the highest amount of reducible interface Ce⁴⁺, leading to a strong interaction with surface Ir species at the metal-support interface during the OSR reaction. The strong interaction induces Ir to be well dispersed on the CL support, and is associated with more redox-active sites (interface Ce⁴⁺/Ce³⁺), to guarantee high activity.     

Effect of surface hydrophilization on Pt/Sibunit catalytic activity in bicyclohexyl dehydrogenation in hydrogen storage application

The dehydrogenation of bicyclohexyl as a liquid organic hydrogen carrier on supported Pt/Sibunit catalysts based on the neutral and partially oxidized supports at a temperature of 320 °C and a space velocity of up to 1.5 h^?1 was studied. The oxidized Sibunit is a more effective support for Pt catalyst in terms of TOF, conversion and selectivity than the neutral carrier. The 3 wt% Pt catalyst shows a higher conversion and selectivity to biphenyl than the 0.5 wt% Pt catalyst on both carriers, but TOF of 0.5 wt% Pt catalyst reaches 238 and 182 mol(H₂)/(gPt * min) for 4 h of the reaction on oxidized Sibunit and neutral Sibunit, respectively. The TOF are 47 and 42 mol(H₂)/(gPt * min) for the corresponding catalysts with a 3 wt% Pt loading.     

The influence of carbon support porosity on the activity of PtRu/Sibunit anode catalysts for methanol oxidation

In this paper we analyse the promises of homemade carbon materials of Sibunit family prepared through pyrolysis of natural gases on carbon black surfaces as supports for the anode catalysts of direct methanol fuel cells. Specific surface area (S_BET) of the support is varied in the wide range from 6 to 415 m² g⁻¹ and the implications on the electrocatalytic activity are scrutinized. Sibunit supported PtRu (1:1) catalysts are prepared via chemical route and the preparation conditions are adjusted in such a way that the particle size is constant within ±1 nm in order to separate the influence of support on the (i) catalyst preparation and (ii) fuel cell performance. Comparison of the metal surface area measured by gas phase CO chemisorption and electrochemical CO stripping indicates close to 100% utilisation of nanoparticle surfaces for catalysts supported on low (22–72 m² g⁻¹) surface area Sibunit carbons. Mass activity and specific activity of PtRu anode catalysts change dramatically with S_BET of the support, increasing with the decrease of the latter. 10%PtRu catalyst supported on Sibunit with specific surface area of 72 m² g⁻¹ shows mass specific activity exceeding that of commercial 20%PtRu/Vulcan XC-72 by nearly a factor of 3.     

Lowering risk of methanation of carbon support in Ru/carbon catalysts for CO methanation by adding lanthanum

Two series of Ru/C catalysts doped with lanthanum ions are prepared and studied in CO methanation in the H₂-rich gas. The samples are characterized by N₂ physisorption, TG-MS studies, XRD, XPS, TEM/STEM and CO chemisorption. Two graphitized carbons differing in surface area (115 and 80.6 m²/g) are used as supports. The average sizes of ruthenium crystallites deposited on their surfaces are 4.33 and 5.95 nm, respectively. The addition of the proper amount of La to the Ru/carbon catalysts leads to an above 20% increase in the catalytic activity along with stable CH₄ selectivity higher than 99% at all temperatures. Simultaneously, lanthanum acts as the inhibitor of methanation of the carbon support under conditions of high temperature and hydrogen atmosphere. Such positive effects are achieved at a very low concentration of La in the prepared samples, a maximum 0.04 La/Ru (molar ratio). 0.01 mmol La introduced to the Ru/C system leads to 98% CO conversion at 270 °C.     

Catalytic supercritical water gasification of aqueous phase directly derived from microalgae hydrothermal liquefaction

Microalgae (N. chlorella) hydrothermal liquefaction (HTL) was conducted at 320 °C for 30 min to directly obtain original aqueous phase with a solvent-free separation method, and then the supercritical water gasification (SCWG) experiments of the aqueous phase were performed at 450 and 500 °C for 10 min with different catalysts (i.e., Pt-Pd/C, Ru/C, Pd/C, Na₂CO₃ and NaOH). The results show that increasing temperature from 450 to 500 °C could improve H₂ yield and TGE (total gasification efficiency), CGE (carbon gasification efficiency), HGE (hydrogen gasification efficiency), TOC (total organic carbon) removal efficiency and tar removal efficiency. The catalytic activity order in improving the H₂ yield was NaOH > Na₂CO₃ > None > Pd/C > Pt-Pd/C > Ru/C. Ru/C produced the highest CH₄ mole fraction, TGE, CGE, TOC removal efficiency and tar removal efficiency, while NaOH led to the highest H₂ mole fraction, H₂ yield and HGE at 500 °C. Increasing temperature and adding proper catalyst could remarkably improve the SCWG process above, but some N-containing compounds were difficult to be gasified. This information is valuable for guiding the treatment of the aqueous phase derived from microalgae HTL.     

Oxygen reduction and hydrogen oxidation reaction on novel carbon supported PdxIry electrocatalysts

In the present work Vulcan XC-72 carbon supported Pd, Ir and Pd_xIr_y (with x:y atomic ratios of 3:1, 1:1, 1:3) electrocatalysts are thoroughly investigated for the reactions of hydrogen oxidation (HOR) and oxygen reduction (ORR). The catalysts are prepared via a pulse-microwave assisted polyol synhtesis method. The techniques of X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) are adopted to investigate the elemental composition, the structure, and the morphology of the as prepared electrocatalysts.Their electrocatalytic properties toward HOR and ORR are evaluated by the aid of cyclic voltammetry (CV) and rotating disk electrode (RDE) techniques. It is found that after the addition of even a small amount of iridium, the electrocatalytic activity of pure palladium is enhanced toward both reactions.According to the obtained results the highest HOR and ORR electrocatalytic activity enhancement is exhibited by PdIr (1:1) sample. The order of the electrocatalytic activity is found to be PdIr > PdIr₃ > Pd₃Ir > Pd > Ir for HOR and PdIr > Pd₃Ir > PdIr₃ > Pd > Ir for the ORR, respectively.     

Carbon dioxide reforming of methane to syngas over ordered mesoporous Ni/KIT-6 catalysts

The ordered mesoporous Ni/KIT-6 (KIT-6, an ordered mesoporous SiO₂) catalysts were prepared by impregnation method for carbon dioxide reforming of methane. The physicochemical properties of the prepared catalysts were characterized by H₂-TPR, XRD, BET, and TEM. The research results show that the specific surface area, pore diameter, crystal size of Ni species, and catalytic performance of the Ni/KIT-6 catalysts are obviously affected by the Ni content. Increasing Ni content results in the increment of the crystal size of Ni species, while the dispersion of Ni species shows the opposite trend. The specific surface area and pore size of the Ni/KIT-6 catalyst with the Ni loading of 3 wt% were 493.3 m² g^?1 and 6.22 nm, respectively. Besides, the Ni species are highly dispersed on the surface of KIT-6 support. Thereby, it exhibits the superior catalytic performance of carbon dioxide reforming of methane to syngas (CO and H₂). At atmospheric pressure, the CO₂ and CH₄ conversions for each catalyst following the order: NK3 ≈ NK4 > NK5 > NK2 > NK1 > bulk Ni. When the reaction temperature is 600 °C, the conversions of CH₄ and CO₂ of the NK3 catalyst are 65.1% and 37.0%, respectively. Meanwhile, it also shows excellent stability.     

Selective catalytic fast pyrolysis of Jatropha curcas residue with metal oxide impregnated activated carbon for upgrading bio-oil

Jatropha curcas waste was subjected to catalytic pyrolysis at 873 K using an analytical pyrolysis–gas chromatography/mass spectrometry in order to investigate the relative effect of various metal oxide/activated carbon (M/AC) catalysts on upgrading bio-oil from fast pyrolysis vapors of Jatropha waste residue. A commercial AC support was impregnated with Ce, Pd, Ru or Ni salts and calcined at 523 K to yield the 5 wt.% M/AC catalysts, which were then evaluated for their catalytic deoxygenation ability and selectivity towards desirable compounds. Without a catalyst, the main vapor products were fatty acids of 60.74% (area of GC/MS chromatogram), while aromatic and aliphatic hydrocarbon compounds were presented at only 11.32%. Catalytic pyrolysis with the AC and the M/AC catalysts reduced the oxygen-containing (including carboxylic acids) products in the pyrolytic vapors from 73.68% (no catalyst) to 1.60–36.25%, with Ce/AC being the most effective catalyst. Increasing the Jatropha waste residue to catalyst (J/C) ratio to 1:10 increased the aromatic and aliphatic hydrocarbon yields in the order of Ce/AC > AC > Pd/AC > Ni/AC, with the highest total hydrocarbon proportion obtained being 86.57%. Thus, these catalysts were effective for deoxygenation of the pyrolysis vapors to form hydrocarbons, with Ce/AC, which promotes aromatics, Pd/AC and Ni/AC as promising catalysts. In addition, only a low yield (0.62–7.80%) of toxic polycyclic aromatic hydrocarbons was obtained in the catalytic fast pyrolysis (highest with AC), which is one advantage of applying these catalysts to the pyrolysis process. The overall performance of these catalysts was acceptable and they can be considered for upgrading bio-oil.     

Room temperature response and enhanced hydrogen sensing in size selected Pd-C core-shell nanoparticles: Role of carbon shell and Pd-C interface

In the present work, the effect of carbon shell around size selected palladium (Pd) nanoparticles on hydrogen (H₂) sensing has been studied by investigating the sensing response of Pd-C core-shell nanoparticles having a fixed core size and different shell thickness. The H₂ sensing response of sensors based on Pd and Pd-C nanoparticles deposited on SiO₂ and graphene substrate has been measured over a temperature range of 25 °C–150 °C. It is observed that Pd-C nanoparticle sensor shows higher sensitivity with increase in shell thickness and faster response/recovery in comparison to that of Pd nanoparticle samples. Pd-C nanoparticles show room temperature H₂ sensitivity in contrast to Pd nanoparticles which respond only at higher temperatures. Role of carbon shell is also understood by investigating H₂ sensing properties of Pd and Pd-C nanoparticles on graphene substrates. These results show that higher catalytic activity and electronic interaction at Pd-C interface, a complete coverage and protection of Pd surface by carbon and presence of structural defects in nanoparticle core are important for room temperature and higher sensing response.     

Porous stainless steel support for hydrogen separation Pd membrane; fabrication by metal injection molding and simple surface modification

We prepared a disc-shaped porous stainless steel (PSS) support for hydrogen separation Pd membrane via metal injection molding (MIM) method to facilitate the mass production of porous substrates. MIMed PSS supports obtained in a batch showed relatively higher apparent porosity (from 32.75% to 39.28%) than that reported for commercially available PSS substrate. In addition, the surface morphologies of the MIMed PSS, surface roughness of 1.119 μm and pore depth of 8.6 μm, indicate its suitability as a membrane support than the commercially available one. Pd membrane prepared over MIMed PSS, which was modified by a simple axial pressing method to control the surface morphologies, had a thinner Pd layer, 2.94 μm, and showed an extremely higher ideal H₂/N₂ selectivity with a hydrogen permeation flux of 21.3 ml/min/cm² at del-P = 1 bar and 400 °C, compared with Pd membrane over MIMed PSS modified with conventional surface modification.     

Electrocatalysis of oxygen reduction when varying the mass ratio of metal nanoparticles to carbon support for catalysts with a 10 to 10 to 80 mol% of Pt and Pd on Ag

The reduction of total Pt-loading in a cathode catalyst without sacrificing performance is one of the key objectives for the large-scale commercialization of proton exchange membrane fuel cell (PEMFC) technology. A core-shell type nanostructured catalyst with a Pt-loading 20 times lower than a commercial catalyst is demonstrated herein to be more active for the electrocatalysis of the oxygen reduction reaction (ORR) in acid electrolyte. The weight ratio of metal nanoparticles on carbon support is the key to achieving the highest ORR activity in a series of silver-based catalysts, all with 10 mol percent of Pt and 10 mol percent of Pd over 80 mol percent of silver (Ag) and supported on untreated Vulcan carbon to form an electrocatalyst (Ag@Pt₁₀Pd₁₀/C) with either 5, 10, 20 or 30 wt% of total metals on carbon; which correspond to a Pt concentration around 1, 2, 3 and 5 wt%, respectively. All metal nanostructures on carbon show a similar morphology, size and structure. Thin films of these four Ag@Pt₁₀Pd₁₀/C catalysts on rotating disk electrodes (TF-RDEs) all shown a 4-electrons pathway for the ORR and give higher exchange current densities (j_o > 3.8 mA/cm²) than a commercial Etek Pt₂₀/C catalyst (j_o = 2.4 mA/cm²). The Ag@Pt₁₀Pd₁₀/C catalyst with 5 wt% of total metals (1 wt% of Pt) on carbon gives the best electrocatalysis; reducing molecular oxygen to water two times faster and generating 25% higher current per milligram of platinum (mass activity) than the commercial catalyst (Pt₂₀/C). Therefore, the Ag@Pt₁₀Pd₁₀/C catalyst with 5 wt% of total metals is a new catalyst for ORR for a PEMFC with a lower Pt loading and cost.     

Effect of support and reduction temperature in the hydrogenation of CO2 over the Cu–Pd bimetallic catalyst with high Cu/Pd ratio

Metal-support interaction and catalyst pretreatment are important for industrial catalysis. This work investigated the effect of supports (SiO₂, CeO₂, TiO₂ and ZrO₂) for Cu–Pd catalyst with high Cu/Pd ratio (Cu/Pd = 33.5) regarding catalyst cost, and the reduction temperatures of 350 °C and 550 °C were compared. The activity based on catalyst weight follows the order of Si > Ce > Zr > Ti when reduced at 350 °C. The reduction temperature leads to the surface reconstruction over the SiO₂, CeO₂ and TiO₂ catalysts, while results in phase transition over Cu–Pd/ZrO₂. The effect of reduction temperature on catalytic performance is prominent for the SiO₂ and ZrO₂ supported catalysts but not for the CeO₂ and TiO₂ ones. Among the investigated catalysts, Zr-350 exhibits the highest methanol yield. This work reveals the importance of the supports and pretreatment conditions on the physical-chemical properties and the catalytic performance of the Cu–Pd bimetallic catalysts.     

A novel Central Composite Design based response surface methodology optimization study for the synthesis of Pd/CNT direct formic acid fuel cell anode catalyst

At present, carbon nanotube supported Pd catalysts are synthesized via NaBH₄ reduction method to investigate their electro catalytic activity thorough formic acid electro oxidation. In order to optimize the synthesis conditions such as %Pd amount (X₁), NaBH₄ amount (times, X₂), water amount (ml, X₃), and time (min., X₄), Central Composite Design (CCD) experiments are designed and determined by the Design-Expert program to determine the maximum observed current (mA/mgPd). Formic acid electro oxidation current density of the catalyst is computed by the model as 974.80 mA/mg Pd for the catalyst prepared at optimum operating conditions (41.14 for %Pd amount, 280.23 NaBH₄ amount, 26.80 ml water amount, and 167.14 min time) obtained with numerical optimization method in CCD. This computed value is very close to the experimentally measured value as 920 mA/mg Pd. Finally, formic acid fuel cell measurements were performed on the Pd/CNT catalyst prepared at optimum operating conditions and compared with the commercial Pd black and Pt black catalysts. As a result, Pd/CNT exhibits better performance compared to Pd black, revealing that Pd/CNT is a promising catalyst for the direct formic acid fuel cell measurements.     

Metal loading effects on carbon-supported Pd electrocatalysts

We report for the first time effects of altering the amount of Pd supported on high-surface area carbon (Pd/C). Cyclic voltammetry in 0.1 M H₂SO₄ using Pd/C electrocatalysts with distinct metal-to-carbon ratio, Pd black and a Pd wire electrodes reveals unambiguously metal loading effects, such as a decrease in the peak potential for the reduction of palladium oxide (PdO), an increase of the charges of desorption of hydrogen, and formation/reduction of PdO with the Pd content. Such effects need to be taken into account when designing Pd-based Fuel Cells electrocatalysts.     

Hydrogen storage properties of various carbon supported NaBH4 prepared via metathesis

Sodium borohydride nanoparticles prepared via the metathesis reaction between LiBH₄ and NaCl were successfully deposited on various carbon supporting materials such as graphite, graphene oxide and carbon nanotubes. The X-ray diffraction analyses were conducted to identify the phase of NaBH₄ deposited on various carbon supporting materials. The transmittance electron micrograph analyses were also conducted to investigate the particle size and dispersion of NaBH₄ within carbon supporting materials. The particle size and size distribution of NaBH₄ on graphite were observed to be larger and broader than of other two supporting materials, graphene oxide and CNT due to the lower surface energy as compared to GO and CNT. The bonding state of NaBH₄ was confirmed by the Fourier-transformed infrared spectroscopy analysis. The TG and PCT results show that the hydrogen desorption of the NaBH₄ deposited on carbon supports takes place at temperature (130 °C～) significantly lower than that of pure NaBH₄ (above 500 °C) and the amount of desorption was in the order of graphene oxide (12.3 mass %) > CNT (9.8 mass %) > graphite (5.7 mass %). The reversibility of hydrogen adsorption after five cycles of adsorption-desorption showed that NaBH₄/GO and NaBH₄/CNT were much better than that of pure NaBH₄ due to excellent structural stability.