Activity In Dry Reforming Research Articles

Dry reforming of methane at moderate temperatures over modified Co-Al Co-precipitated catalysts

M-Co-Al (M = Ca, La, Li or Mg) materials were synthesised by co-precipitation and investigated for dry reforming of methane. Thermogravimetry, temperature-programmed oxidation, reduction and CO2 desorption, specific area and X-ray diffraction were utilised for characterisation. Activity tests were conducted at atmospheric pressure, temperatures between 400-550oC , CH4/CO2 molar ratio of 1 and GHSV of 6000 NmL CH4·g-1·h-1. The partial substitution of Co by a third element increased the area and changed the acid/base properties, reducibility and crystallinity of the oxides. These modifications resulted in higher activity for dry reforming of methane, mainly related to the decrease in the acidity of the promoted materials and, consequently, lower carbon formation. The Li-modified sample presented the lowest coke deposition due to the increase in stronger basic sites. The Mg-promoted catalyst exhibited the best activity performance. This depicts the enhancement in the reducibility and acid/base properties found in the MgCoAl sample.

Palladium nanoparticle's surface structure and morphology effect on the catalytic activity for dry reforming of methane

Low loaded Pd/α-Al2O3 catalysts (<0.5wt% Pd) were characterized and tested for CH4 reforming with CO2 at 650°C. The catalysts were prepared by a recharging procedure, using an organometallic precursor, followed by intermediate washing and calcination steps. FTIR spectra of adsorbed CO showed that the Pd surface structure and the particle size were dependent on the number of post-impregnation washing steps. A catalyst sample with a metal dispersion of 33% showing well defined low-index planes (by FTIR) and nearly spherical particles (by TEM) was obtained using two-washing steps. In the reaction, it exhibited a high initial activity followed by a pronounced deactivation due to carbon nanofiber's formation and sintering. TEM analysis of the used catalyst revealed the presence of spherical Pd particles at the end of the fibers that were not attached to the support surface. On the other hand, a high dispersion sample (78%) with a large fraction of Pd atoms with low coordination was obtained by applying three washing steps after impregnation. The presence of small hemispherical particles and larger nearly-flat ones attached to the support were found by TEM. In this case, the catalyst initially showed a very low activity that increased slowly up to a steady value. Although sintering also occurred and the surface structure of the used catalyst resembled the one of the low dispersion catalyst, the amount of carbon formed was quite low. The observed activation under reaction conditions was associated with the slow development of a surface structure that exhibited mainly the (100) plane favoring methane dissociation. However, the initial interaction of the particles with the support suggested by TEM micrographs seems to remain unaltered despite the particle size increase. Consequently, the process of nanofiber formation and particle separation was inhibited.

Insights into dynamic surface processes occurring in Rh supported on Zr-grafted γ-Al2O3 during dry reforming of methane

γ-Al2O3 support was modified with zirconia by the grafting method, using zirconium(IV) n-propoxide as precursor. Rh catalysts were prepared by wet impregnation of pure γ-Al2O3 (Rh/A), Zr modified γ-Al2O3 (Rh/100Z-A), and pure ZrO2 (Rh/Z) supports. Rh/A presents a good activity in dry reforming of methane and exhibits a high amount of surface oxidized rhodium (92% of surface Rh atoms) after the reaction. Rh/Z is poorly active and 45% of Rh surface atoms remain reduced during the reaction. The catalytic activity significantly increased when using Rh/100Z-A. Tetragonal ZrO2 crystallites are formed on the surface of modified alumina. It was obtained that, after Rh deposition, the grafted catalyst is composed by Rh/A and Rh/Z, as separated catalytic particles in good contact. To further understand the high activity of the grafted catalyst, mechanical mixtures of Rh/A and Rh/Z catalysts were synthesized. Compared with the single catalysts, an important synergistic effect in methane conversion and yields to CO and H2 was observed when high amounts of Rh/A were mixed with Rh/Z catalyst, along with a promotion of rhodium oxidation in Rh/Z, which leads to a high surface fraction of RhOx (88%) in the mixture. The formation of mixed phases between the supports and the migration of Rh atoms from one phase to the other were discarded. It is suggested that a catalytic cooperation occurs due to the presence and mobility of oxygen species generated by the dissociation of CO2 on Rh/A, which migrate to the Rh/Z catalyst promoting the oxidation of rhodium at its surface, and the catalytic activity. This cooperation mechanism is also expected to operate in the Rh/100Z-A catalyst, between the Rh/A and Rh/Z particles present in the surface. The importance of oxidized Rh for dry reforming of methane is evident from the high catalytic activity achieved when highly oxidized rhodium atoms are present together with the metallic Rh sites where methane activation occurs.

Catalytic Dry Reforming of Methane on Ruthenium-Doped Ceria and Ruthenium Supported on Ceria

Two types of Ru–ceria catalysts were investigated, one prepared by combustion to create an atomically doped metal oxide, and the other, prepared by impregnation, as supported Ru oxide. They have different physical properties (as measured by X-ray photoelectron spectroscopy, X-ray diffraction, and Infrared spectra of adsorbed CO) but identical catalytic activity for dry reforming of methane. We show that the catalyst for dry reforming is partially reduced using XPS and IR spectroscopy. Furthermore, transient oxidation reaction spectroscopy with oxygen pulses confirms partial reduction of the catalyst is necessary for dry reforming activity.

Sol-derived AuNi/MgAl2O4 catalysts: Formation, structure and activity in dry reforming of methane

Ni nanoparticles doped with different amount of gold were supported on MgAl2O4 by deposition from aqueous metal sol producing a series of catalysts with different Au content. The sol procedure was allowed to obtain dispersed metal particles with different composition. The particle size and the particle composition of the sol were maintained even after being deposited on the support. The catalysts, characterized by several techniques such as TPR, XPS, XRD, TEM, HRTEM and EELS at the different stages of their life exhibited significant structural modification. In particular, thermal treatments in reducing and oxidizing environment produced NiAu alloy phases and NiO surface segregation, respectively. When testing for methane dry reforming with CO2 in temperature ramped reaction, the monometallic nickel catalyst was more active at lower temperature whereas the bimetallic catalysts were more active at higher temperature. The presence of gold slightly affected the CO/H2 ratio due to the occurrence of parallel reactions such as the reverse water gas shift reaction (RWGS). Both types of catalysts, monometallic and bimetallic ones, deactivated a little with time but the degree of activity loss was not in straightforward relation with Au content due to the different effect of gold on the stability and on the amount of carbon formation.

Mesoporous amorphous silicate catalysts for biogas reforming

A number of Ni-TUD-1 amorphous materials with different content of Ni (from 0 to 10wt%) was synthesized. The materials activity in dry reforming of methane (DRM) was compared and the optimal amount of Ni in the catalyst was evaluated. A Ni content of 3wt% in the amorphous silicate matrix of TUD-1 structure was chosen as the most active amongst the synthesized materials. The materials were tested in DRM both with argon dilution (different amount of diluting gas) and without diluting gas. It was shown that Ni-TUD-1 catalytic materials could be used in biogas reforming process in real conditions. The reaction outgas of the biogas (model mixture of 35mol% CO2 and 75mol% CH4) reforming test at 750°C was composed of 20vol% of H2. In general, it was shown that TUD-1 materials could be promising supports for Ni allowing its high dispersion in the silicate matrix. The same amorphous porous matrix was found to insure the stability of the Ni-TUD-1 catalysts to carbon deposition.

Structural studies of nanosized porous membrane catalytic systems highly active in dry reforming of biomass conversion products

The structures of porous ceramic membrane catalytic systems exhibiting high activity in dry reforming of biomass conversion products (methane, hydrocarbons C2–C4, and alcohols) to a hydrogen-containing gas were studied. The membrane catalytic systems represent porous inorganic membranes (supports) prepared by self-propagating high-temperature synthesis and modified by nanosized metallocompex components, which are uniformly distributed in the internal pore volume. Structural studies were carried out using scanning electron microscopy with energy dispersive analysis, transmission electron microscopy, temperature-programmed reduction with hydrogen, and X-ray diffraction analysis.

The Effect of CeO&lt;sub&gt;2&lt;/sub&gt; and Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Dopants on Ni/ Alumina Based Catalyst for Dry Reforming of Methane to Hydrogen

Methane reforming is the most feasible techniques to produce hydrogen for commercial usage. Hence, dry reforming is the environment friendly method that uses green house gases such as CO2and methane to produce fuel gas. Catalysts play a vital role in methane conversion by enhancing the reforming process. In this study Ni/γ-Al2O3was selected as based catalyst and CeO2and Fe2O3dopants were added to investigate their effect on catalytic activity in dry reforming. The catalysts synthesized through wet impregnation method and characterized by using XRD, TEM and SEM-EDX. The catalytic tests were carried out using temperature programmed reaction (TPRn) and the products were detected by using an online mass spectrometer. The results revealed that these dopants significantly affect the catalytic activity and selectivity of the catalyst during reaction. Hence, Fe2O3doped catalyst shows higher hydrogen production with stable catalytic activity.

Activity and stability enhancement of Ni-MCM-41 catalysts by Rh incorporation for hydrogen from dry reforming of methane

Ni incorporated and Ni–Rh incorporated bimetallic MCM-41 like mesoporous catalysts, which were synthesized following a one-pot hydrothermal procedure, showed very high activity in dry reforming of methane. Among the Ni incorporated catalysts, Ni-MCM-41-V, with a Ni/Si ratio of 0.19, showed the best catalytic performance. Rh incorporation into this catalyst by the one-pot procedure improved both activity and time on stream stability of the catalyst. However, Rh incorporation by impregnation caused instabilities due to coke formation, after about 11 h of reaction time. Occurrence of reverse water gas shift reaction caused higher CO selectivity than H 2 selectivity, with the Ni incorporated catalysts. Rh incorporation into these catalysts decreased the relative significance of reverse water gas shift reaction, with respect to dry reforming reaction.

The effect of impregnation strategy on methane dry reforming activity of Ce promoted Pt/ZrO 2

Dry reforming of methane has been studied over Pt/ZrO 2 catalysts promoted with Ce for different temperatures and feed compositions. The influence of the impregnation strategy and the cerium amount on the activity and stability of the catalysts were investigated. The results have shown that introduction of 1 wt.% Ce to the Pt/ZrO 2 catalyst via coimpregnation method led to the highest catalytic activity and stability. 1 wt.%Ce–1 wt.%Pt/ZrO 2 catalyst prepared by sequential impregnation displayed inferior CH 4 and CO 2 conversion performances with lowest H 2/CO production ratios. 1 wt.%Ce–1 wt.%Pt/ZrO 2 catalyst prepared by coimpregnation showed the highest activity even for the feed with high CH 4/CO 2 ratio. The reason for high activity was explained by the intensive interaction between Pt and Ce phases for coimpregnated sample, which had been verified by X-ray photoelectron spectroscopy and Energy Dispersive X-Ray analyses. Strong and extensive Pt–Ce surface interaction results in an increase in the number of Ce 3+ sites and enhances the dispersion of Pt.

Effect of adding CaO to ZrO 2 support on nickel catalyst activity in dry reforming of methane

Nickel catalysts with a load of 5 wt% Ni, supported on pure ZrO 2 and ZrO 2 stabilized with 4, 8 and 14 mol% CaO, were prepared by the polymerization method. The samples were characterized by X-ray diffraction (XRD), temperature-programmed reduction with hydrogen (TPR-H 2), specific surface area (BET) and impedance spectroscopy (IS) and tested in the carbon dioxide reforming of methane. The XRD patterns showed the presence of the oxide precursor (NiO) and the tetragonal phase of CaO–ZrO 2 solid solutions. According to the TPR-H 2 analysis, the reduction of various NiO species was influenced by the support composition. The electrical properties of the support have a proportional effect on the catalytic activities. Catalytic tests were done at 800 °C for 6 h and the composition of the gaseous products and the catalytic conversion depended on the CaO–ZrO 2 solid solution composition and its influence on supported NiO species. A direct relation was found between the variation in the electrical conductivity of the support, the nickel species supported on it and the performance in the catalytic tests.

Characterization and activity in dry reforming of methane on NiMg/Al and Ni/MgO catalysts

Dry reforming of methane has been investigated on two series of catalysts either prepared by co-precipitation: n(Ni x Mg y )/Al, Ni x Mg y and Ni x Al y or prepared by impregnation: Ni/MgO (mol% Ni = 5, 10). The catalysts, calcined at 600–900 °C, were characterized by different techniques: BET, H 2-TPR, TPO, XRD, IR, and TEM-EDX analysis. The surface BET (30–182 m 2 g −1) decreased with increasing the temperature of calcination, after reduction and in the presence of Mg element. The XRD analysis showed, for n(Ni x Mg y )/Al catalysts, the presence of NiAl 2O 4 and NiO–MgO solid solutions. The catalyst reducibility decreased with increasing the temperature of pretreatment. The n(Ni x Mg y )/Al catalysts were active for dry reforming of methane with a good resistance to coke formation. The bimetallic catalyst Ni 0.05Mg 0.95 (calcined at 750 °C and tested at 800 °C) presents a poor activity. In contrast, the 5% Ni/MgO catalyst, having the same composition but prepared by impregnation, presents a high activity for the same calcination and reaction conditions. For all the catalysts the activity decreased with increasing the temperature of calcination and a previous H 2-reduction of the catalyst improves the performances. The TPO profiles and TEM-EDX analysis showed mainly four types of coke: CH x species, surface carbon, nickel carbide and carbon nanotubes.

Synthesis gas production from dry reforming of methane over CeO2 doped Ni/Al2O3: Influence of the doping ceria on the resistance toward carbon formation

Abstract Doping of CeO2 as an additive promoter on Ni/Al2O3 was found to improve dry reforming activity for H2 and CO productions at solid oxide fuel cell (SOFC) operating temperature (800–900 °C). The catalyst provides significantly higher reforming reactivity and resistance toward carbon deposition compared to conventional Ni/Al2O3. These enhancements are mainly due to the influence of the redox property of ceria. During dry reforming process, in addition to the reactions on Ni surface, the gas–solid reactions between the gaseous components presented in the system (CH4, CO2, CO, H2O, and H2) and the lattice oxygen (Ox) on ceria surface also take place. The reactions of adsorbed methane and carbon monoxide (produced during dry reforming process) with the lattice oxygen (Ox) on ceria surface (CH4 + Ox → CO + H2 + Ox−1 and CO + Ox ⇔ CO2 + Ox−1) can prevent the formation of carbon species on Ni surface from methane decomposition reaction and Boudard reaction. In particular, CeO2 doped Ni/Al2O3 with 8% ceria content showed the best reforming activity among those with the ceria content between 0 and 14%. The amount of carbon formation decreased with increasing Ce content. However, Ni was oxidized when more than 10% of ceria was doped. According to the post-XPS measurement, a small formation of Ce2O3 was observed after exposure in dry methane reforming conditions with low inlet CH4/CO2 ratio (1.0/0.3). The intrinsic reaction kinetics of 8% CeO2 doped Ni/Al2O3 was studied by varying inlet CH4 and CO2 concentrations, and by adding H2 and CO to the system at different temperatures. The dry reforming rate increased with increasing methane partial pressure and the operating temperature. The reaction orders in methane were always closed to 1.0 in all conditions. Carbon dioxide also presented weak positive impact on the methane conversion, whereas adding of carbon monoxide and hydrogen inhibited the reforming rate.

Catalytic dry reforming of methane over high surface area ceria

High surface area ceria (CeO2 (HSA)), synthesized by a surfactant-assisted approach, was found to have useful dry reforming activity for H2 and CO production under solid oxide fuel cells (SOFCs) conditions. The catalyst provides significantly higher reforming reactivity and excellent resistance toward carbon deposition compared to Ni/Al2O3 and conventional low surface area ceria (CeO2 (LSA)) under dry reforming conditions. These enhancements are due to the high redox property of CeO2 (HSA). During the dry reforming process, the redox reactions between the gaseous components in the system and the lattice oxygen (Ox) take place on ceria surface. Among these reactions, the rapid redox reactions of carbon compounds such as CH4, and CO with lattice oxygen (CH4+Ox→CO+H2+Ox−1 and CO+Ox=CO2+Ox−1) can prevent the formation of carbon species from the methane decomposition and Boudard reactions even at low inlet carbon dioxide concentration.In particular, the dry reforming rate over CeO2 (HSA) is proportional to the methane partial pressure and the operating temperature. Carbon dioxide presents weak positive impact on the methane conversion, whereas both carbon monoxide and hydrogen inhibit the reforming rate. The activation energies and reforming rates under the same methane concentration for CeO2 toward the dry reforming are almost equal to the steam reforming as previously reported [1–4]. This result suggests the similar reaction mechanisms for both the steam reforming and the dry reforming over CeO2; i.e., the dry reforming rate is governed by the slow reaction of adsorbed methane, or surface hydrocarbon species, with oxygen in CeO2, and a rapid gas–solid reaction between CO2 and CeO2 to replenish the oxygen.

Strontium carbonate supported cobalt catalyst for dry reforming of methane under pressure

Catalytic performance of Co–SrO catalyst for dry reforming of methane was investigated at 1 MPa, 1023 K. The catalyst prepared by oxalate co-precipitation method or citric acid method showed a steady activity for dry reforming of methane under pressure. The importance and stability of cobalt metal with strontium carbonate were suggested for the Co–SrO catalyst, and thus it should be denoted as Co–SrCO 3. In addition, cobalt supported on strontium carbonate prepared by impregnation method (Co/SrCO 3) showed the comparable activity with high tolerance to oxidative atmosphere under reaction conditions.