Types Of Carbon Species Research Articles

Effect of O2 and temperature on the catalytic performance of Ni/Al2O3 and Ni/MgAl2O4 for the dry reforming of methane (DRM)

Al2O3 and MgAl2O4 supported 10% (w/w) Ni catalysts having a dispersion of 1.5 and 2.0% are active for DRM at 600 and 750 °C. High temperature reduction of both the calcined catalysts resulted in metallic Ni being formed, suggesting strong support metal interactions. The CH4 and CO2 conversion during DRM are relatively constant with time-on-stream, and are higher for Ni/MgAl2O4 than Ni/Al2O3. Carbon-whiskers are also detected on both catalysts. O2 co-feed of 2.6% (v/v) and increasing reaction temperature to 750 °C helped in decreasing the amount of carbon deposited, except for Ni/MgAl2O4 at 600 °C. Furthermore, higher conversions and H2/CO ratios are achieved. It appears that on spent Ni/MgAl2O4 a different type of carbon species was formed, and this carbon species was difficult to remove by oxygen at 600 °C. Thus, co-feeding O2, using an appropriate temperature, and choosing a suitable support can reduce the carbon present on the nickel catalysts during DRM.

Can formate dehydrogenase from Candida boidinii catalytically reduce carbon dioxide, bicarbonate, or carbonate to formate?

It was found that CbFDH was catalytically reduce only carbon dioxide to formate among the three types of carbonate species, carbon dioxide, bicarbonate and carbonate for the first time.

Synergy between sodium carbonate and sodium titanate nanotubes in the transesterification of soybean oil with methanol

Abstract Sodium titanate nanotubes (STN) modified by the addition of sodium carbonate (3–10 wt. %) were tested as catalysts for the transesterification of soybean oil with methanol giving good results. Prepared catalysts were characterized by N2 physisorption, X-ray diffraction, FT-IR, temperature-programmed desorption of CO2, scanning and transmission electron microscopy. The STN catalysts modified with sodium carbonate were significantly more active in the transesterification reaction than the reference catalyst containing 5 wt. % of Na2CO3 on alumina. The most active catalyst, STN with 10 wt. % of Na2CO3, resulted in the 97% yield of methyl esters at a short reaction time (30 min) in mild conditions (80 °C). High activity of the prepared catalysts was attributed to a synergetic effect between the support and the deposited sodium carbonate leading to a noticeable increase in the amount of strong basic sites able to generate methoxide anions required for the transformation of triglycerides to methyl esters. According to the FT-IR characterization, the above synergy was attributed to the presence of different types of carbonate species in the alumina and STN-supported catalysts. Upon reutilization, Na2CO3-containing STN catalysts showed a decrease in their activity due to leaching of the active phase in the reaction media.

A variable temperature infrared spectroscopy study of CaA zeolite dehydration and carbonate formation.

Variable temperature diffuse reflection infrared spectroscopy is used to monitor the dehydration of calcium enriched Linde type A zeolite (CaA). Infrared spectrum changes indicate that the energy imparted to the zeolite by heating causes water desorption and also facilitates reactions between water and zeolite framework, yielding SiOHAl acid sites. Water also reacts with ambient carbon dioxide producing carbonic acid, which readily dissociates to form carbonate. Three types of carbonate species are reported. The most thermally stable carbonate is coordinated to Ca2+ as a monodentate ligand. A second carbonate-containing species may be simultaneously interacting with Ca2+ and the zeolite framework. The third type of carbonate is characterized by infrared absorption consistent with a highly symmetric configuration, suggesting weak interactions with the local environment. Temperature-dependent infrared spectrum variations suggest that protons from carbonic acid dissociations react with framework and Ca(OH)+ moieties, altering internal CaA pore structure configurations.

Hydrogen production from glycerol dry reforming over Ag-promoted Ni/Al2O3

Abstract In recent times, glycerol has been employed as feedstock for the production of syngas (H2 and CO) with H2 as its main constituent. This study centers on dry reforming of glycerol over Ag-promoted Ni/Al2O3 catalysts. Prior to characterization, the catalysts were synthesized using the wet impregnation method. The reforming process was carried out using a fixed bed reactor at reactor operating conditions; 873–1173 K, carbon dioxide to glycerol ratio of 0.5 and gas hourly space velocity (WHSV) in the range of 14.4 ≤ 72 L gcat−1 h−1). Ag (3)-Ni/Al2O3 gave highest glycerol conversion and hydrogen yield of 40.7% and 32%, respectively. The optimum conditions which gave highest H2 production, minimized methane production and carbon deposition were reaction temperature of 1073 K and carbon dioxide to glycerol ratio of 1:1. This result can attributed to the small metal crystallite size characteristics possessed by Ag (3)–Ni/Al2O3, which enhanced metal dispersion in the catalyst matrix. Characterization of the spent catalyst revealed the formation of two types of carbon species; encapsulating and filamentous carbon which can be oxidized by O2.

Morphology-Dependent Properties of Cu/CeO2 Catalysts for the Water-Gas Shift Reaction

CeO2 nanooctahedrons, nanorods, and nanocubes were prepared by the hydrothermal method and were then used as supports of Cu-based catalysts for the water-gas shift (WGS) reaction. The chemical and physical properties of these catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption/desorption, UV-Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), hydrogen temperature-programmed reduction (H2-TPR) and in situ diffuse reflectance infra-red fourier transform spectroscopy (DRIFTS) techniques. Characterization results indicate that the morphology of the CeO2 supports, originating from the selective exposure of different crystal planes, has a distinct impact on the dispersion of Cu and the catalytic properties. The nanooctahedron CeO2 catalyst (Cu-CeO2-O) showed the best dispersion of Cu, the largest amount of moderate copper oxide, and the strongest Cu-support interaction. Consequently, the Cu-CeO2-O catalyst exhibited the highest CO conversion at the temperature range of 150–250 °C when compared with the nanocube and nanorod Cu-CeO2 catalysts. The optimized Cu content of the Cu-CeO2-O catalysts is 10 wt % and the CO conversion reaches 91.3% at 300 °C. A distinctive profile assigned to the evolution of different types of carbonate species was observed in the 1000–1800 cm−1 region of the in situ DRIFTS spectra and a particular type of carbonate species was identified as a potential key reaction intermediate at low temperature.

Renewable hydrogen from glycerol reforming over nickel aluminate-based catalysts

Nickel aluminate (NiAl2O4) was synthesized by citrate method and used as a precursor for supported Ni catalysts. This bulk sample as well as an alumina-supported NiAl2O4 and a dual catalytic system obtained by its simple and straightforward physical mixture with alumina were investigated on glycerol reforming at different water:glycerol molar ratio conditions. All catalyst precursors and the reduced catalysts made thereof were characterized by XRF, porosity, H2-TPR, powder XRD and temperature-resolved XRD. Spent catalysts were complementarily analyzed by TPO/TGA-MS and FE-SEM in order to infer on deactivation process. NiAl2O4 precursor structure rendered highly active systems accomplishing a level of glycerol conversion to gaseous products roughly equivalent to glycerol global conversion. Therefore, hydrogen and CO2 were the main products obtained, reaching hydrogen yields usually higher than 80% with respect to the theoretical maximum production. The way NiAl2O4 phase is settled in catalyst formulation (bulk, supported or physically mixed) revealed an important influence on catalyst deactivation. Deactivation was associated with the formation of carbon filaments as no other type of carbon species, more or less reactive, could be identified.

Solid-State 13C NMR Spectroscopy Applied to the Study of Carbon Blacks and Carbon Deposits Obtained by Plasma Pyrolysis of Natural Gas

Solid-state 13C nuclear magnetic resonance (NMR) spectroscopy was used in this work to analyze the physical and chemical properties of plasma blacks and carbon deposits produced by thermal cracking of natural gas using different types of plasma reactors. In a typical configuration with a double-chamber reactor, N2 or Ar was injected as plasma working gas in the first chamber and natural gas was injected in the second chamber, inside the arc column. The solid residue was collected at different points throughout the plasma apparatus and analyzed by 13C solid-state NMR spectroscopy, using either cross polarization (CP) or direct polarization (DP), combined with magic angle spinning (MAS). The 13C CP/MAS NMR spectra of a number of plasma blacks produced in the N2 plasma reactor showed two resonance bands, broadly identified as associated with aromatic and aliphatic groups, with indication of the presence of oxygen- and nitrogen-containing groups in the aliphatic region of the spectrum. In contrast to DP experiments, only a small fraction of 13C nuclei in the plasma blacks are effectively cross-polarized from nearby 1H nuclei and are thus observed in spectra recorded with CP. 13C NMR spectra are thus useful to distinguish between different types of carbon species in plasma blacks and allow a selective study of groups spatially close to hydrogen in the material.

Carbon gasification from Fe–Ni catalysts after methane dry reforming

Carbon species removal was studied from a Fe–Ni catalyst supported on MgAl2O4 after methane dry reforming at 1023K, atmospheric pressure and a CH4/CO2 molar ratio of 1:1. The deactivated and regenerated catalysts were characterized using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and energy-dispersive X-ray spectroscopy (EDX)-STEM mapping. The catalyst regeneration was studied by CO2 and O2 temperature programmed oxidation (TPO) and by operando time-resolved X-ray diffraction (XRD). A transient response technique, Temporal analysis of products (TAP), was applied to investigate the isothermal carbon species gasification.Two different types of carbon species, graphitic and amorphous, were present after reaction. CO2 oxidation could remove part of the carbon species, although EDX-STEM mapping showed the presence of carbon species located far from active metals phase even after CO2–TPO at 1123K. Carbon species removal by CO2 involves two contributions: (1) the dissociation of CO2 over Ni followed by the oxidation of carbon species by surface oxygen; (2) Fe oxidation by CO2 and subsequent carbon species oxidation by Fe oxide lattice oxygen. The oxidation of carbon species by O2 was identified from temperature programmed and isothermal experiments as a process including two processes: (1) oxidation of surface carbon by lattice oxygen and (2) particles migration to carbon species deposited far from active metals and subsequent oxidation through lattice oxygen of the iron and/or nickel oxides. The contribution of oxygen spillover in carbon gasification was considered to be negligible.

Carbon deposition behavior of a Co–Ni aerogel catalyst in CH4 oxy-CO2 reforming using various types of reactors

Carbon deposition behavior of a Co–Ni aerogel catalyst in CH4 oxy-CO2 reforming is investigated using a deactivation method in three types of reactors including a magnetic field assisted fluidized bed (MAFB) reactor, a conventional fluidized bed reactor and a fixed bed reactor. The spent catalysts are analyzed by TG/DSC and FESEM. It is found that the reactor influences the amount as well as type of carbon species on the spent catalysts. The amount of carbon on the spent catalyst in the MAFB reactor is 11.7 wt.%, which is 10.8 wt.% and 2.6 wt.% less than those in the fixed bed and conventional fluidized bed reactors. Fluidization behavior analysis reveals that agglomerate and bubble size of the catalyst are obviously decreased with the application of the MAFB, which should be accounted for the enhanced carbon resistance of the reactor.

Fischer–Tropsch Synthesis on Co/Al2O3 Catalyst: Effect of Pretreatment Procedure

The effect of pretreatment procedure on catalytic performance during Fischer–Tropsch synthesis (FTS) of unpromoted cobalt on alumina (15 %Co/Al2O3) catalyst was studied in a fixed-bed reactor. Pure carbon monoxide or a mixture of hydrogen and carbon monoxide were used as reducing agents prior to FTS. Pretreatments with pure CO result in low activity and high selectivity to methane and gaseous hydrocarbons in comparison to standard hydrogen reduction. The use of synthesis gas (H2/CO = 2/1) as a reducing agent resulted in high initial activity and high selectivity to gaseous hydrocarbons. Pretreatment procedure that utilized synthesis gas after the CO reduction resulted in low activity but high selectivity to high molecular weight hydrocarbons. Catalyst performance is strongly affected by the presence of cobalt carbides, cobalt oxide and/or various types of carbon species on the surface as determined by X-ray diffraction and temperature-programmed hydrogenation and oxidation characterization techniques.

Surfactant-free preparation of nickel carbonate hydroxide in aqueous solution and its toxic ion-exchange properties

In this paper, we have demonstrated a simple surfactant-free solution method for the synthesis of sea urchin-like nickel carbonate hydroxide, which was characterized by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, thermal gravimetric analysis, nitrogen adsorption–desorption isotherms, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Two types of carbonate species, a surface unidentate carbonate-like species and a crystal lattice carbonate species, were proposed based on the FTIR and symmetry analysis. The toxic ion-exchange properties towards As(V), Cd(II), and Cu(II) ions were investigated. At pH 5.0, the exchange capacities of Cd(II) and Cu(II) ions were 120.5 and 109.3 mg g−1, respectively, through the ion-exchange between nickel ions with them, which was confirmed by XPS. For As(V) ion removal, the maximum exchange capacity was 49.6 mg g−1 without any pH adjustment, which should be of importance for water treatment. Furthermore, a novel ion-exchange mechanism between the surface unidentate carbonate-like species and As(V) ions was proposed, which was revealed by XPS and FTIR.

A Photoemission Study of Ethylene Decomposition on a Co(0001) Surface: Formation of Different Types of Carbon Species

We have studied the interaction of ethylene on Co(0001) in detail by X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). At 130 K, the chemisorption and decomposition of C2H4 were found to depend on the vacant sites available on Co(0001). C2H4 chemisorbs dissociatively at low exposures but both dissociatively and molecularly at large exposures. Upon heating, some C2H4(a) desorbs molecularly from the surface, releasing vacant surface sites that result in the simultaneous decomposition of other C2H4(a). C2H2(a) is the surface intermediate for the decomposition of C2H4(a) on Co(0001). At elevated temperatures, C2H2(a) simultaneously undergoes the direct dehydrogenation and the cyclopolymerization–dehydrogenation to form surface C2 cluster and graphitic carbon on Co(0001). At 500 K, C2H4 directly decomposes on Co(0001), forming surface atomic carbon. These results provide novel information on the chemisorption and decomposition of C2H4 on Co(0001) and the nature of resulted carbon species, greatly deepening our fundamental understanding of the relevant heterogeneous catalytic reactions catalyzed by Co-based catalysts and the growth of graphene on Co surfaces by chemical vapor deposition.

The promoting effect of La, Mg, Co and Zn on the activity and stability of Ni/SiO 2 catalyst for CO 2 reforming of methane

CO 2 reforming of methane into synthesis gas over Ni/SiO 2 catalysts promoted by La, Mg, Co and Zn was investigated. The catalysts were prepared by impregnation method and characterized by XRD, TPR, SEM and TG-DTA techniques. Ni–La/SiO 2 catalyst was found to exhibit high activity and excellent stability with the addition of suitable amount of La promoter, which increased the dispersion of NiO and the interaction between NiO and SiO 2. Two different types of carbon species, namely, easily oxidized carbonaceous species and inert carbon, were observed on the surface of the used catalysts. The inert carbon deposited on Ni–Mg/SiO 2 catalyst may be the main reason for its deactivation, while the principal reason for the deactivation of Ni–Co/SiO 2 catalyst might be the sintering of metallic Ni. The addition of La and Mg decreased the contribution of reverse water-gas shift reaction, leading to higher H 2 yield.

Methane dry reforming with CO 2: A study on surface carbon species

Methane dry reforming with a mixture of 29% CO 2 and 71% CH 4 over 8 wt% NiMgAl 2O 4 in a plug flow reactor with temperature programmed mode has been investigated. It was established that in sequential reactions the catalyst was deactivated due to graphite like carbon deposit measured by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) while by X-ray photoelectron spectroscopy (XPS) only Ni–carbide was observed. The discrepancy found by XPS and TEM can be explained by the different types of carbon species, i.e. it is assumed that after the first reaction mostly carbide is deposited, whereas after several subsequent reactions the carbon on the surface is graphitized forming carbon nanotubes (TEM). Addition of 0.5 wt% gold to NiMgAl 2O 4 improves the catalytic activity and on gold containing bimetallic catalyst the formation of nanotubes is vanished. The results are interpreted by the formation of non-crystalline NiC x which – depending on the conditions – is transferred to graphitic carbon species.

Characterization and Analysis of Carbon Deposited during the Dry Reforming of Methane over Ni/La2O3/Al2O3 Catalysts

Ni/La2O3/γ-Al2O3 and Ni/La2O3/α-Al2O3 catalysts were prepared by the incipient wetness impregnation and evaporation methods. Their catalytic properties for the dry reforming of methane without a diluting gas were studied. The fresh and used catalysts and deposited carbon were characterized by H2 temperature-programmed reduction, N2 adsorption-desorption, X-ray diffraction, transmission electron microscopy, thermogravimetry coupled to differential scanning calorimetry, and temperature-programmed hydrogenation. The results showed that there were four carbon species that existed as three types, namely, amorphous (polymeric), filamentous, and graphitic carbon. The amount and type of carbon species on the catalysts depended on the size of Ni particles and texture of the support. The formation and morphology of filamentous carbon were clearly related to the size of Ni particles. Ni particles less than 15 nm suppressed the formation and deposition of filamentous carbons, decreased the amount of carbon deposition, and had more active Cα species, resulting in a better activity and higher stability of the catalysts.

Carbon dioxide reforming of methane to synthesis gas over Ni-MCM-41 catalysts

A series of nickel incorporated MCM-41 mesoporous molecular sieves (Ni-MCM-41) were prepared by direct hydrothermal synthesis. Nickel nitrate was used as the Ni precursor. The catalytic properties of the Ni-MCM-41 were studied for the reforming of methane with carbon dioxide. The catalysts were carefully characterized by X-ray diffraction (XRD), N 2 physisorption, H 2 temperature-programmed reduction (TPR), H 2 chemisorption, thermogravimetry, and Raman spectra. The results indicated that the presence of a suitable amount of nickel in Ni-MCM-41 was beneficial for maintaining high catalytic activity and long-term stability. The improved catalytic performance was suggested to closely associate with both the amount of active centers on the pore wall surface and the stabilized dispersion of these active sites by the silica matrix and/or the surrounding unreduced nickel ions. This anchoring effect facilitated the formation of the active Ni nano-clusters with high dispersion under reaction conditions. Hence the reforming reaction is favored and the carbon formation is suppressed. Two types of carbon species: active carbon and graphite were produced over the spent catalysts. The Ni-MCM-41 catalysts provided good catalytic activity, high stability and reasonable CO/H 2 ratios in the product. Thus, the Ni-MCM-41 catalyst prepared by the direct hydrothermal synthesis promised a novel and stable catalyst candidate for CO 2 reforming of CH 4.

Selective production of hydrogen via oxidative steam reforming of methanol using Cu–Zn–Ce–Al oxide catalysts

The oxidative steam reforming of methanol (OSRM) was carried out to produce the hydrogen selectively for polymer electrolyte membrane (PEM) fuel cell applications over Cu–Zn–Ce–Al oxide and Cu–Zn–Al oxide catalysts of varying compositions prepared by co-precipitation method. Catalyst performance was evaluated in a packed bed reactor over a wide range of operating conditions, and reaction parameters were optimized in order to maximize the hydrogen production with minimum carbon monoxide formation. The incorporation of ceria in Cu–Zn–Al oxide catalysts enhanced the activity greatly compared to without it. The Cu/Zn/Ce/Al:30/20/10/40 exhibited 100% methanol conversion and 244 mmol s - 1 kg cat - 1 hydrogen rate at 553 K with carbon monoxide as low as 995 ppm, which reduces the load on preferential oxidation of CO to CO 2 significantly before feeding the hydrogen rich stream to the PEM fuel cell as a feed. Ceria had improved the dispersion and specific surface area of copper in multi-component Cu–Zn–Ce–Al oxide catalysts which were confirmed by the physicochemical properties, X-ray diffraction (XRD), temperature programmed reduction (TPR) and CO chemisorption studies. The chemisorption studies were performed at 193 K in order to hinder the spillover of carbon monoxide to ceria. The time-on-stream stability test had shown Cu–Zn–Ce–Al oxide catalysts as more stable compared to Cu–Zn–Al oxide catalysts. The amount of carbon deposited onto the catalysts was determined using TG/DTA thermogravimetric analyzer and the type of carbon species were identified using C1s X-ray photoelectron spectroscopy (XPS) spectra.

Ru-Mo/HZSM-5 Catalyzed Methane Aromatization in Membrane Reactors

Oxygen-free methane conversion into benzene was carried out in a catalytic membrane reactor over 0.5%Ru-3%Mo/HZSM-5 in the temperature range 873-973 K following three reaction protocols: (i) straight-run catalytic reactor without hydrogen permeation (OFF), (ii) cycled OFF/ON hydrogen permeation sequences, and (iii) cycled OFF/ON hydrogen permeation sequences intertwined with CH4/H2 regenerative steps. X-ray photoelectron spectroscopy analysis of fresh and spent catalysts identified, in all cases, three types of carbon species that formed during aromatization, including carbide formation. The presence of a permeating membrane did not give rise to different chemical states of carbon and molybdenum on the catalyst from those known to form in straight runs under no hydrogen permeation. The ON mode, i.e., during permeation, led to the accumulation of graphite-like and aromatic-aliphatic (coke) species on the catalyst. However, both types of carbon were reduced during the OFF step either by autogenous hydrogen or via an external source of hydrogen under CH4/H2 regenerative steps.

Internal reforming over nickel/zirconia anodes in SOFCS oparating on methane: influence of anode formulation, pre-treatment and operating conditions

Internal methane reforming over nickel/zirconia cermet anodes has been studied in detail using a thin-walled extruded zirconia tubular SOFC reactor. The influence of anode formulation, anode pre-treatment, operating temperature and methane/steam ratio on the reforming characteristics, resistance to carbon deposition and durability of the anode have been investigated under actual operating conditions. Post-reaction TPO has been used to determine the amount of carbon deposition and its strength of interaction with the anode. A 90-vol.% nickel/zirconia anode shows higher activity than a 50-vol.% Ni anode at higher reforming temperatures, and shows very good durability. Pre-reducing the anodes in H 2 at 1173 K leads to a more active reforming catalyst. Carbon is removed from the anodes in two processes during TPO, suggesting two types of carbon species. As the reforming temperature increases both carbon types are removed at higher temperature, and there is an increase in the relative population of the more strongly bound form of carbon.