Mixed Reforming Research Articles

Kinetics modeling for the mixed reforming of methane over Ni-CeO 2/MgAl 2O 4 catalyst

Abstract Kinetics model was developed for the mixed (steam and dry) reforming of methane, which is useful for the control of H 2/CO ratio. The equilibrium constants of reaction rate were determined using the experimental equilibrium data at different reaction temperatures, while the forward reaction rate constants were estimated using the experimental data under non-equilibrium (high inert fraction and high space velocity) conditions. The comparison between calculated and experimental data clearly showed that the developed model described satisfactorily, and further analysis using the parametric sensitivity determined the wall temperature and CO 2 fraction in the feed gas as effective parameters for the manipulation of CH 4 conversion and H 2/CO ratio of synthesis gas under the equilibrium condition. Meanwhile, the inert fraction, rather than the residence time, was selected as additional parameter under non-equilibrium condition.

Stability improvements of Ni/α-Al 2O 3 catalysts to obtain hydrogen from methane reforming

Ni catalysts supported on commercial α-Al 2O 3 modified by addition of CeO 2 and/or ZrO 2 were prepared in the present work. Since the principal objective was to evaluate the behavior of these systems and the support effect on the stability, methane reforming reactions were studied with steam, carbon dioxide, partial oxidation and mixed reforming. Results show that catalysts supported on Ce–Zr–α-Al 2O 3 composites present better reforming activity and stability noticeably higher than in the case of the reference support. With respect to composites, the presence of mixed oxides of Ce xZr 1−xO 2 type facilitates the formation of active phases with higher interaction. This fact reduces the deactivation by sintering conferring to the system a higher contribution of adsorbed oxygen species, favoring the deposited carbon elimination. These improvements resulted in being dependent on the Ce:Zr ratio of the composite, thus obtaining more stable catalysts for Ce:Zr = 4:1 ratios.

06/02559 Mixed reforming of heptane to syngas in the Ba0.5Sr.5Co0.8Fr0/2O3 membrane reactorZhu, W. et al. Catalysis Today, 2005, 104, (2–4), 149–153

06/02559 Mixed reforming of heptane to syngas in the Ba0.5Sr.5Co0.8Fr0/2O3 membrane reactorZhu, W. et al. Catalysis Today, 2005, 104, (2–4), 149–153

Mixed reforming of simulated gasoline to hydrogen in a BSCFO membrane reactor

Currently, fuel cells are receiving more and more attention as the most promising new power generation technology, and fuel processing by the mixed reforming of liquid hydrocarbons (MRL) with water and oxygen is regarded as a desirable way for fuel cells. In this paper, we developed a new mixed reforming method for hydrogen production by combining a dense ceramic membrane Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ (BSCFO) with a catalyst LiLaNiO/γ-Al 2O 3 in a membrane reactor and reforming a simulated gasoline. During a 500-h long-term test at optimized reaction conditions, all the components in the simulated gasoline converted completely, and around 90% selectivity of CO, around 95% selectivity of H 2 and around 8.0 mL cm −2 min −1 oxygen permeation flux were achieved. This provides a new optional way of hydrogen production for fuel cells.

Mixed reforming of heptane to syngas in the Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3 membrane reactor

Fuel cells are recognized as the most promising new power generation technology, but hydrogen supply is still a problem. In our previous work, we have developed a LiLaNiO/γ-Al 2O 3 catalyst, which is excellent not only for partial oxidation of hydrocarbons, but also for steam reforming and autothermal reforming. However, the reaction needs pure oxygen or air as oxidant. We have developed a dense oxygen permeable membrane Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3 which has an oxygen permeation flux around 11.5 ml/cm 2 min at reaction conditions. Therefore, this work is to combine the oxygen permeable membrane with the catalyst LiLaNiO/γ-Al 2O 3 in a membrane reactor for hydrogen production by mixed reforming of heptane. Under optimized reaction conditions, a heptane conversion of 100%, a CO selectivity of 91–93% and a H 2 selectivity of 95–97% have been achieved.

Study of Ni catalysts on different supports to obtain synthesis gas

Ni catalysts supported on α -Al 2O 3, ZrO 2 and α -Al 2O 3–ZrO 2 were studied in the synthesis gas reactions (partial oxidation, dry reforming and mixed reforming). The Ni/ α -Al 2O 3–ZrO 2 catalyst showed a very good performance in relation to the initial activity and selectivity, comparable to that of the Ni/ α -Al 2O 3 catalyst. Concerning the deactivation, the modification of the α -Al 2O 3 supported with ZrO 2 leads to a higher stability, due to the strong inhibition of the carbon formation during the reaction. These results suggest that ZrO 2 promotes the gasification of adsorbed intermediates, which are precursors of carbon formation. Temperature programmed oxidation, transmission electron microscopy and Raman spectroscopy experiments showed that on Ni/ α -Al 2O 3 catalyst high amounts of graphitic carbon (whisker-like) are deposited during CO 2 reforming reaction, while on Ni/ α -Al 2O 3–ZrO 2 lesser amounts of deposited carbon were observed (about one order lower); a fraction of this carbon is of the same nature as that observed on Ni/ α -Al 2O 3 catalyst, while the other fraction is composed of carbon nanotubes, both of single wall and multi wall.

Comparison of Partial Oxidation and Steam-CO2Mixed Reformingof CH4to Syngas on MgO-Supported Metals

Partial oxidation (POX) and steam-CO2mixed reforming of CH4on MgO-supported noble metals were investigated at high spacevelocity (5.5×105h−1). Temperature-programmedreaction (TPR) and isotope transient techniques were used tostudy the mechanism of POX and mixed reforming. TPR profiles ofPOX and mixed reforming showed similar ignition reactionbehaviors, which implied that there are similar characteristicsin their mechanisms. Steam reforming and CO2reforming werefound to start at the same time in mixed reforming. TPR andCH4–D2exchange experiments indicated that CH4wasactivated at low temperature on Rh/MgO. POX showed much higheractivity than mixed reforming although their C, H, and O atomicconcentrations were the same at the beginning of each reaction.It is suggested that the lower rate of reaction in mixedreforming is due to the blocking of active sites for CH4activation by CO2and H2O. It seems that the coexistenceof CO2and H2O shows stronger inhibition than that ofCO2alone and H2O alone.Rh/MgO without previous reductiontreatment also showed a high reactivity for POX but with ahigher ignition temperature than a prereduced catalyst. Withregard to the H2/CO ratio, mixed reforming showed a changingratio with increasing temperature, which suggested that the ratefor CO2reforming increases faster than that of steamreforming. Anin situisotope-labelled13CO2transient experiment for mixed reforming indicated that carbonformed from CO2or CO decomposition was less active than(CHx)ad(x=0, 1, 2, and 3) formed from CH4decomposition.For POX, a small amount of steam had little effect on COformation rate for an active catalyst, e.g., Rh/MgO or Ru/MgO,but decreased the rate for less active catalyst Pt/MgO. All theresults indicated that steam reforming and CO2reforming inmixed reforming start simultaneously and have the same type ofreaction intermediate, adsorbed atomic oxygen. POX proceeds viaboth one-step and two-step mechanisms, the ratio for eachmechanism being dependent on the concentration and kinetics ofadsorbed atomic oxygen and gaseous atomic oxygen. Mechanismsfor POX and mixed reforming are suggested and the effect ofoxygen–metal bond strength on activity is discussed.

Study of mixed steam and CO 2 reforming of CH 4 to syngas on MgO-supported metals

The activity of mixed steam and CO 2 reforming of CH 4 to produce synthesis gas was investigated and compared with those of steam reforming alone and CO 2 reforming alone at 600–900°C under atmosphere pressure on MgO-supported noble metals. Mixed reforming shows a far lower CH 4 conversion than the value for thermodynamic equilibrium. The activity decreases following the order Ru,Rh > Ir > Pt,Pd. Little deactivation was observed for Ru, Rh and Ir catalysts. An isotope labelled 13CO 2 experiment was carried out in situ for mixed reforming on Rh/MgO and the results suggest that CO 2 dissociates as CO-M and O-M. The results of the temperature program reaction (TPR) of mixed reforming shows that CH 4 adsorbs and dissociates before reaction starts and that CO 2 reforming and steam reforming start simultaneously. A possible reaction mechanism is discussed.