La-promoted Catalysts Research Articles

Study on the effect of promotors in CO2 utilization for syngas production via dry reforming of methane over Co-MOX/TiO2-Al2O3 (MOX = La, Ce, Mg, and K) catalysts

In this study, Co-based catalysts supported over Ti-Al oxide and promoted with La, Ce, Mg, and K metals were assessed for CO2 reforming of methane reaction to produce syngas. Titania-alumina mixed oxide supports were prepared using the template-assisted-solvothermal method, and then Co and promotors were co-impregnated over the as-prepared support. Different characterizations of catalysts showed that variation in promotor metal impacts these catalysts' physical and chemical properties. The Ti-Al oxide support possessed the perfect hexagonal morphology. Potassium-promoted catalysts possessed the highest number of basic sites, whereas the La-promoted catalyst possessed the highest number of acidic sites. La promotion improved the Co dispersion, while Mg promotion enhanced the metal support integration. La-promoted catalysts are deactivated because of active metal oxidation and the generation of hard carbon. The carbon was deposited in all catalysts; however, the activity of the Mg-promoted catalyst was unaffected. The intermediate surface basicity and strong metal support interaction improved the Mg-promoted catalyst's stability. The La and Mg-promoted catalysts possessed lower apparent activation energies.

Greenhouse gas mitigation and hydrogen generation via enhanced ethylene glycol dry reforming on La-promoted Co/Al2O3 catalyst

The first investigation of La-promoted Co/Al2O3 catalysts in Ethylene Glycol-CO2 conversion (EGCC) for syngas (H2 + CO) production was conducted in this work. Co/Al2O3 catalysts modified with different La promoter loadings (1, 3, and 5%) were generated through sequential incipient wetness impregnation technique and employed for EGCC. The physicochemical attributes of the generated catalysts were examined via Brunauer-Emmett-Teller (BET), H2 temperature-programmed reduction (H2-TPR), X-ray diffraction (XRD), Raman, and temperature-programmed oxidation (TPO). 3%La-promoted catalyst owned the largest specific surface area, smallest Co crystallite size of 9.8 nm, and lowest reduction temperature among the promoted catalysts. These excellent properties resulted in the highest catalytic performance on the 3%La-promoted catalyst (i.e., C2H6O2 conversion = 77.6 %, CO2 conversion = 43.1 %, H2 yield = 75.3 %, and CO yield = 76.8 %). The significant reduction in carbon deposition of the 3%La-promoted catalyst was due to the La capability in eliminating deposited carbon via the formation of intermediate lanthanum dioxycarbonate, La2O2CO3.

Continuous CO2 capture and reduction in one process: CO2 methanation over unpromoted and promoted Ni/ZrO2

The recently demonstrated concept to combine CO2 capture and utilization in one process using isothermal unsteady-state operation, namely CO2 capture and reduction (CCR), was applied for CO2 methanation using unpromoted and K- or La-promoted Ni/ZrO2 catalysts. Both K and La promoters significantly improve CO2 capture capacity and also the selectivity of CO2 conversion to methane. The K-promoted catalyst (Ni-K/ZrO2) captures a larger amount of CO2 at high temperature but the capture capacity drops at low temperature due to incomplete catalyst regeneration during the cyclic unsteady-state reaction condition. In contrast, the La-promoted catalyst (Ni-La/ZrO2) shows temperature-independent CO2 capture capacity and rapid reduction of captured CO2, thus leading to stable CCR performance. The nature of the active sites and mechanistic details were gained by TPR, reductive CO2-TPD and space- and time-resolved operando DRIFTS, holistically elucidating the effects of the promoters and their impacts on CCR activity.

La-promoted Ni-hydrotalcite-derived catalysts for dry reforming of methane at low temperatures

La-promoted Ni-containing hydrotalcite-derived catalysts were prepared and tested in dry methane reforming at low-moderate temperatures. The prepared materials were characterized by means of X-ray diffraction (XRD), temperature programmed reduction (H2-TPR) and CO2-temperature programmed desorption (TPD). The presence of lanthanum was found to enhance the reforming reaction, but also direct methane decomposition at low reaction temperatures. This fact was assigned to an increased presence of Ni0 sites as a consequence of improved reducibility of Ni-species in the La-promoted catalysts. Lanthanum can well contribute to the gasification of amorphous carbon deposits, resulting in lower overall carbon deposition at 550°C.

Influence of Lanthanide Promoters on Ni/SBA-15 Catalysts for Syngas Production by Methane Dry Reforming

The catalytic performance of Ce- and La-promoted Ni/SBA-15 catalysts for syngas production from CO2 reforming of methane has been investigated in a fixed-bed reactor at stoichiometric feed composition. Both promoted and unpromoted catalysts possessed high BET surface area of 303-445 m2 g-1. Additionally, SBA-15 support had a relatively uniform rod-like shape with a diameter of about 0.55μm and a reduction in the crystallite size of NiO phase from 27.0 to 19.1nm was observed with promoter addition reasonably due to the strong interaction between promoter and NiO particles. CeO2 and La2O3 dopants were finely dispersed on catalyst surface. Temperature-programmed oxidation of spent catalysts showed that coke-resistance was improved significantly with promoter modification and 3%La-10%Ni/SBA-15 catalyst was the most resistant to carbonaceous deposition rationally due to the least NiO crystallite size hindering the nucleation and growth of graphitic carbon. Hence, La-promoted catalyst appeared to be the optimum catalyst in terms of reactant conversion, H2 yield and stability whilst a gradual decline in both reactant conversion and H2 yield was experienced with unpromoted and Ce-doped catalysts. Regardless of catalyst types, the ratio of H2 to CO was always less than unity preferred for Fischer-Tropsch synthesis.

Syngas production by combined steam and CO2 reforming of coke oven gas over highly sinter-stable La-promoted Ni/MgAl2O4 catalyst

Highly sinter-stable 10 wt% Ni–xLa/MgAl2O4 (x = 0–5 wt%) catalysts were prepared by co-impregnation for the combined steam and CO2 reforming (CSCR) of coke oven gas (COG). The physicochemical properties of the catalysts were analyzed by BET, XRD, H2 chemisorption, and H2-TPR. To compare the sinterstabilities, aging treatment was performed at 900 °C under H2:H2O:N2 = 1:10:1.25 for 50 h. Although the Ni dispersions decrease and Ni crystallite sizes increase for all of catalysts after the aging treatment, the La-promoted catalysts had higher Ni dispersion and smaller crystallite sizes than the Ni/MgAl2O4 catalyst owing to the enhancement of strong metal-support interactions. The catalytic test was carried out under CH4:H2O:CO2:H2:CO:N2 = 1:1.2:0.4:2:0.3:0.3 at 900 °C and 5 atm for 40 h. The Ni–2.5La/MgAl2O4 (aged) catalyst exhibited the highest activity and sinterstability owing to its high surface area and Ni dispersion. It was also confirmed that La promotion prevents the agglomeration of Ni particles through TEM.

Syngas production from glycerol-dry(CO2) reforming over La-promoted Ni/Al2O3 catalyst

A 3 wt% La-promoted Ni/Al2O3 catalyst was prepared via wet co-impregnation technique and physicochemically-characterized. Lanthanum was responsible for better metal dispersion; hence higher BET specific surface area (96.0 m2 g−1) as compared to the unpromoted Ni/Al2O3 catalyst (85.0 m2 g−1). In addition, the La-promoted catalyst possessed finer crystallite size (9.1 nm) whilst the unpromoted catalyst measured 12.8 nm. Subsequently, glycerol dry reforming was performed at atmospheric pressure and temperatures ranging from 923 to 1123 K employing CO2-to-glycerol ratio from zero to five. Significantly, the reaction results have yielded syngas as main gaseous products with H2:CO ratios always below than 2.0 with concomitant maximum 96% glycerol conversion obtained at the CO2-to-glycerol ratio of 1.67. In addition, the glycerol consumption rate can be adequately captured using power law modelling with the order of reactions equal 0.72 and 0.14 with respect to glycerol and CO2 whilst the activation energy was 35.0 kJ mol−1. A 72 h longevity run moreover revealed that the catalyst gave a stable catalytic performance.

Mo–Co–K Sulfide-Based Catalysts Promoted by Rare Earth Salts for Selective Synthesis of Ethanol and Mixed Alcohols from Syngas

Abstract Mo–Co–K sulfide-based catalysts promoted by rare earth metal salts (La, Ce, and Y) were prepared by an ultrasonic technology in a non-aqueous medium. The catalytic performance for the selective synthesis of ethanol and mixed alcohols from syngas was evaluated and compared with that of the unpromoted catalyst Mo–Co–K. Under the reaction conditions of 3.0 MPa, 330°C, H2/CO(V/V) = 2.0, and GHSV = 2225 h−1, the CO conversion and ethanol distribution over the La-promoted catalyst were 17.2% and 53.4%, respectively. The results of SEM, TEM, XRD, Raman, and XPS characterization indicated that the morphology and electronic structure of the catalysts changed, and the CO conversion and ethanol distribution increased after the addition of rare earth promoters.

Isotopic transient analysis of ammonia synthesis over Ru/MgO catalysts promoted by cesium, barium, or lanthanum

The global and intrinsic kinetics of ammonia synthesis over ruthenium supported on MgO (∼2 wt% Ru) and promoted with Cs, Ba, or La were examined at 3 atm and various dihydrogen pressures with steady-state and isotopic transient measurements. Steady-state, global measurements revealed that Cs–Ru/MgO was strongly inhibited by dihydrogen whereas Ba–Ru/MgO and La–Ru/MgO were weakly inhibited by the reactant. However, the isotopic transient measurements showed that the intrinsic turnover frequency was a weak positive function of dihydrogen pressure regardless of the added base. Promotion by these compounds appeared to be electronic in nature because their presence increased the intrinsic turnover frequency of an active site, with Cs being the most effective. However, the coverage of nitrogen-containing intermediates was greater on Ba- and La-promoted catalysts than on Cs–Ru/MgO at 673 K and stoichiometric conditions. Therefore, the global activity of a promoted catalyst is a competition between inhibition by dihydrogen and enhancement of dinitrogen dissociation. Furthermore, promotion with Cs, Ba, and La introduced a new and highly active class of sites to the Ru/MgO system.

CO2 Reforming of CH4 over Pt/ZrO2 Catalysts Promoted with La and Ce Oxides

The CO2 reforming of CH4 was studied over cerium- and lanthanum-promoted Pt/ZrO2 catalysts at 1073 K and a CH4 : CO2 ratio of 2 : 1. The high ratios of CH4 : CO2 were used in an attempt to accelerate deactivation of the catalyst and make a faster comparison of the different samples. The addition of Ce resulted in a significant improvement in the stability, with no decrease in either CH4 or CO2 conversion observed. The promotion with La also resulted in an increase in the stability of the catalyst as well as an increase in the initial activity. The mechanism of reaction has been studied on the promoted catalysts, and it has been shown that it is not altered by the presence of the promoters. The long-term activity of the catalyst is dependent upon the balance between the rate of CH4 decomposition and the rate of dissociation of CO2. The results of pulse studies demonstrate that addition of the cerium results in an increase in the reducibility and oxygen transfer ability of the support. Temperature-programmed oxidation studies demonstrated that although the total amount of carbon deposits on the Ce-promoted catalyst is not lower than that on the unpromoted one, these deposits are eliminated at much lower temperature, indicating the ability of the catalyst to clean the active sites. On the other hand, the TPO studies on the La-doped catalyst showed a much lower extent of carbon deposition. Interestingly, the ability of La to inhibit carbon formation is only observed in the presence of CO2. Under pulses of pure CH4, the La-promoted catalyst was the one which showed the highest tendency for carbon deposition. X-ray diffraction and BET area characterization of this catalyst showed that the promoter increases the thermal stability of the support. Finally, it was shown that the promoters also retard metal particle growth during reaction at high temperature. Smaller Pt particles result in an increase in the interfacial area and subsequent increase in the removal of the carbon from the metal. The increase in the efficiency of the cleaning mechanism resulted in catalysts that were stable for the dry reforming reaction under severely deactivating conditions (i.e., 1073 K, CH4 : CO2 ratio=2 : 1) for over 20 h.

Promoted Fe/ZSM-5 catalysts prepared by sublimation: de-NOx activity and durability in H 2 O-rich streams

Fe/ZSM-5 catalysts with an Fe/Al ratio 1:0, were prepared by sublimation of FeCl3 into H/ZSM-5. They display high activity and durability for the selective catalytic reduction of NOx to N2, both in dry and wet gas flows. These catalysts have now been modified by exchanging a second cation into the zeolite. Mere neutralization of zeolite protons by Na+ lowers the selectivity for NOx reduction to N2, but the cations Ce3 + and La3 + act as true catalyst promoters. With isobutane as the reductant in a simulated vehicular emission gas, almost 90% of NOx is reduced to N2 at 350°C over the La-promoted catalyst. The presence of 10% H2O in the feed does not impair the catalyst performance at high temperature; in the temperature region below 350°C it even increases the N2 yield. The beneficial effect of La is due to its lowering of the catalyst activity for the undesired combustion of the hydrocarbon. No signs of zeolite destruction are evident after 100 h TOS in a wet gas flow at 350°C. Carbonaceous deposits causing a slight deactivation are easily removed in an O2/He flow at 500°C; this in situ regeneration fully restores the original activity.