Daniel J. Haynes

Role of metal substitution in lanthanum zirconate pyrochlores (La2Zr2O7) for dry (CO2) reforming of methane (DRM)

Dry (CO2) reforming of methane (DRM) produces syngas with H2/CO ratio of ≤1. In this work, we report the use of pyrochlores (A2B2O7) as catalysts for this reaction. Here, we examine lanthanum zirconate pyrochlores, LZ, with lanthanum and zirconium occupying the A and B sites, respectively. Three catalysts are tested: LZ and two pyrochlores in which the B-site has been isomorphically substituted with (a) Ru (2 wt%) (designated LRuZ) and (b) Pt (3.78 wt%) (designated LPtZ). These levels of substitution by weight correspond to identical atomic levels of substitution at the B-site. The effect of isomorphic substitution of Ru and Pt on the structure and activity of the pyrochlores in DRM is studied in this work. ICP-OES, XRD, H2 and CH4 TPR were used to characterize the structure of the catalysts. XRD results confirmed the formation of the La2Zr2O7 phase in the bulk of the pyrochlores. H2 TPR showed higher reduction temperatures for LPtZ compared to LRuZ, suggesting a less reducible, stable Pt in the pyrochlore structure compared to Ru. Quantitative analysis showed that LRuZ consumed 0.534xa0mg H2/gcat, whereas LPtZ consumed only 0.161xa0mg H2/gcat corresponding to much greater extent of reduction for LRuZ compared to LPtZ. CO formation during CH4 TPR showed that both materials have reactive lattice oxygen which helps in reducing carbon formation during DRM. Temperature programmed oxidation studies of the catalyst immediately after CH4 TPR showed greater carbon formation over LPtZ (1.67 gc/gcat) compared to LRuZ (1.17xa0gc/gcat) suggesting that Pt activates CH4 to a greater extent compared to Ru. Temperature programmed DRM surface reaction showed that the light off temperature for LRuZ was about 45xa0°C lower than that of LPtZ. These are novel results and constitute the first report of which we are aware for Pt and Ru substituted pyrochlores for DRM.

Characterization and activity study of the Rh-substituted pyrochlores for CO2 (dry) reforming of CH4

Isomorphic substitution of Rh at varying levels on the B site of lanthanum zirconate pyrochlore (La2Zr2O7; designated LZ) resulted in the formation of thermally stable catalysts suitable for fuel reforming reactions operating at 900xa0°C. Three specific catalysts are reported here: (a) unsubstituted lanthanum zirconate (LZ), (b) LZ with 2 wt% substituted Rh (L2RhZ), and (c) LZ with 5 wt% substituted Rh (L5RhZ). These catalysts were characterized by XRD, XPS, and H2-TPR. XRD of the fresh, calcined catalysts showed the formation of the pyrochlore phase (La2Zr2O7) in all three materials. In L5RhZ, the relatively high level of Rh substitution led to the formation of LaRhO3 perovskite phase which was not observed in the L2RhZ and LZ pyrochlores. TPR results show that the L5RhZ consumed 1.57xa0mg H2/gcat, which is much greater than the 0.508xa0H2/gcat and 0.155xa0mgxa0H2/gcat for L2RhZ and LZ, respectively, suggesting that the reducibility of the pyrochlore structure increases with increasing Rh-substitution. DRM was studied on these three catalysts at three different temperatures of 550, 575, and 600xa0°C. The results showed that CH4 and CO2 conversion was significantly greater for L5RhZ compared to L2RhZ and no activity was observed for LZ, suggesting that the surface Rh sites are required for the DRM reaction. Temperature programmed surface reaction showed that L5RhZ had light-off temperature 80xa0°C lower than L2RhZ. The spent catalysts after runs at each temperature were characterized by temperature programmed oxidation (TPO) followed by temperature programmed reduction and XRD. The TPO results showed that the amount of carbon formed over L5RhZ is almost half of that formed on L2RhZ.

Oxidative Steam Reforming

Publisher Summary This chapter explores aspects of oxidative steam reforming (OSR) chemistry that are important in a fuel-reforming process. In this method, steam and oxygen are fed together as oxidants to reform the hydrocarbon fuel into a H2-rich fuel stream suitable for fuel cells. OSR is generally considered as a combination of partial oxidation and steam reforming. Feeding air and steam together utilizes the heat generated from exothermic oxidation of the fuel to promote the endothermic steam-reforming reactions. OSR has been an established technology for H2 generation since the late 1950s. It is capable of producing H2 efficiently at high throughputs, which generally makes it the preferred method for industrial use in petrochemical production. However, using OSR for such applications requires a separation plant to remove N2 from air to reduce process gas volumes. Oxygen separation is very capital intensive (almost 40% of total cost) and generally precludes the use of OSR for large-scale applications. However, OSR does have some disadvantages. Using steam requires a water storage and supply system, which adds weight, complexity, and cost to the process. Also, as with any system that uses water, appropriate insulation is needed for applications in colder climates, and added space would be required for a reservoir in an already confined area (assuming for transportation use). Attempts to mitigate storage problems have looked into recycling the fuel cell exhaust to provide the necessary water requirements to maintain reforming capabilities under OSR conditions.

Glycine–nitrate synthesis of Sr doped La2Zr2O7 pyrochlore powder

Abstract Abstract Materials with A2B2O7 (pyrochlore) structure have received significant attention for their applications as new protonic conductors and materials used in electronic devices. One of the unique synthesis routes for La2Zr2O7 (pyrochlore) powders is the glycine–nitrate combustion method, which shows superior properties of the synthesised powder using glycine as a complexing agent. The Sr doped La2Zr2O7 powders in pure pyrochlore structure were produced using this approach. Selected characteristics of the synthesised powders, such as crystal structure, lattice parameters, crystallite size, the vibrational properties, the morphology of the particles, along with the specific surface area and particle size, have been investigated. The dependence of some properties on annealing temperatures of the powders has been studied.

Characterization of LaRhO3 perovskites for dry (CO2) reforming of methane (DRM)

This work reports on the characterization of LaRhO3 perovskite as a catalyst for dry reforming of methane. The catalyst was studied using CH4-temperature programmed reduction (TPR), H2-TPR, and temperature programmed surface reaction (TPSR), and the changes in the crystal structure of the catalyst due to these treatments were studied by X-ray diffraction (XRD). XRD pattern of the freshly calcined perovskites showed the formation of highly crystalline LaRhO3 and La2O3 phases. H2-TPR of the fresh calcined catalyst showed a shoulder at 342°C and a broad peak at 448°C, suggesting that the reduction of Rh in perovskite occurs in multiple steps. XRD pattern of the reduced catalyst suggests complete reduction of the LaRhO3 phase and the formation of metallic Rh and minor amounts of La(OH)3. The CH4-TPR data show qualitatively similar results as H2-TPR, with a shoulder and a broad peak in the same temperature range. Following the H2-TPR up to 950°C, the same batch of catalyst was oxidized by flowing 5 vol. % O2/He up to 500°C and a second H2-TPR (also up to 950°C) was conducted. This second H2-TPR differed significantly from that of the fresh calcined catalyst. The single sharp peak at 163°C in the second H2-TPR suggests a significant change in the catalyst, probably causedby the transformation of about 90 % of the perovskite into Rh/La2O3. This was confirmed by the XRD studies of the catalyst reduced after the oxidation at 500°C. TPSR of the dry reforming reaction on the fresh calcined catalyst showed CO and H2 formation starting at 400°C, with complete consumption of the reactants at 650°C. The uneven consumption of reactants between 400°C and 650°C suggests that reactions other than DRM occur, including reverse water gas shift (RWGS) and the Boudouard reaction (BR), probably as a result of in-situ changes in the catalyst, consistent with the H2-TPR results. TPSR, after a H2-TPR up to 950°C, showed that the dry reforming reaction did not light off until 570°C, which is much higher temperature than the one observed using fresh calcined catalyst. This shows that the uniform sites produced during the 950°C H2-TPR are catalytically less active than those of the fresh calcined catalyst, and that no significant side reactions such as RWGS or the Boudouard reaction occur. This suggests that reduction leads to the formation of a single type of sites which do not catalyze simultaneous side reactions.

Characterization of LaRhO 3 perovskites for dry (CO 2 ) reforming of methane (DRM)

This work reports on the characterization of LaRhO3 perovskite as a catalyst for dry reforming of methane. The catalyst was studied using CH4-temperature programmed reduction (TPR), H2-TPR, and temperature programmed surface reaction (TPSR), and the changes in the crystal structure of the catalyst due to these treatments were studied by X-ray diffraction (XRD). XRD pattern of the freshly calcined perovskites showed the formation of highly crystalline LaRhO3 and La2O3 phases. H2-TPR of the fresh calcined catalyst showed a shoulder at 342°C and a broad peak at 448°C, suggesting that the reduction of Rh in perovskite occurs in multiple steps. XRD pattern of the reduced catalyst suggests complete reduction of the LaRhO3 phase and the formation of metallic Rh and minor amounts of La(OH)3. The CH4-TPR data show qualitatively similar results as H2-TPR, with a shoulder and a broad peak in the same temperature range. Following the H2-TPR up to 950°C, the same batch of catalyst was oxidized by flowing 5 vol. % O2/He up to 500°C and a second H2-TPR (also up to 950°C) was conducted. This second H2-TPR differed significantly from that of the fresh calcined catalyst. The single sharp peak at 163°C in the second H2-TPR suggests a significant change in the catalyst, probably causedby the transformation of about 90 % of the perovskite into Rh/La2O3. This was confirmed by the XRD studies of the catalyst reduced after the oxidation at 500°C. TPSR of the dry reforming reaction on the fresh calcined catalyst showed CO and H2 formation starting at 400°C, with complete consumption of the reactants at 650°C. The uneven consumption of reactants between 400°C and 650°C suggests that reactions other than DRM occur, including reverse water gas shift (RWGS) and the Boudouard reaction (BR), probably as a result of in-situ changes in the catalyst, consistent with the H2-TPR results. TPSR, after a H2-TPR up to 950°C, showed that the dry reforming reaction did not light off until 570°C, which is much higher temperature than the one observed using fresh calcined catalyst. This shows that the uniform sites produced during the 950°C H2-TPR are catalytically less active than those of the fresh calcined catalyst, and that no significant side reactions such as RWGS or the Boudouard reaction occur. This suggests that reduction leads to the formation of a single type of sites which do not catalyze simultaneous side reactions.

Characterization of perovskite LaRhO3 for dry (CO2) reforming of methane (DRM)

This work reports on the characterization of LaRhO3 perovskite as a catalyst for dry reforming of methane. The catalyst was studied using CH4-temperature programmed reduction (TPR), H2-TPR, and temperature programmed surface reaction (TPSR), and the changes in the crystal structure of the catalyst due to these treatments were studied by X-ray diffraction (XRD). XRD pattern of the freshly calcined perovskites showed the formation of highly crystalline LaRhO3 and La2O3 phases. H2-TPR of the fresh calcined catalyst showed a shoulder at 342°C and a broad peak at 448°C, suggesting that the reduction of Rh in perovskite occurs in multiple steps. XRD pattern of the reduced catalyst suggests complete reduction of the LaRhO3 phase and the formation of metallic Rh and minor amounts of La(OH)3. The CH4-TPR data show qualitatively similar results as H2-TPR, with a shoulder and a broad peak in the same temperature range. Following the H2-TPR up to 950°C, the same batch of catalyst was oxidized by flowing 5 vol. % O2/He up to 500°C and a second H2-TPR (also up to 950°C) was conducted. This second H2-TPR differed significantly from that of the fresh calcined catalyst. The single sharp peak at 163°C in the second H2-TPR suggests a significant change in the catalyst, probably causedby the transformation of about 90 % of the perovskite into Rh/La2O3. This was confirmed by the XRD studies of the catalyst reduced after the oxidation at 500°C. TPSR of the dry reforming reaction on the fresh calcined catalyst showed CO and H2 formation starting at 400°C, with complete consumption of the reactants at 650°C. The uneven consumption of reactants between 400°C and 650°C suggests that reactions other than DRM occur, including reverse water gas shift (RWGS) and the Boudouard reaction (BR), probably as a result of in-situ changes in the catalyst, consistent with the H2-TPR results. TPSR, after a H2-TPR up to 950°C, showed that the dry reforming reaction did not light off until 570°C, which is much higher temperature than the one observed using fresh calcined catalyst. This shows that the uniform sites produced during the 950°C H2-TPR are catalytically less active than those of the fresh calcined catalyst, and that no significant side reactions such as RWGS or the Boudouard reaction occur. This suggests that reduction leads to the formation of a single type of sites which do not catalyze simultaneous side reactions.

La1.97Sr0.03Zr2O7 Pyrochlore Powder for Advanced Energy Application

Materials with A2B2O7 (pyrochlore) structure have received a significant attention for their applications as new protonic conductors and materials used in electronic devices. One of the unique synthesis routes for La2Zr2O7 (pyrochlore) powders is the glycine-nitrate combustion method, which shows superior properties of the synthesized powder by using glycine as a complexing agent. The Sr doped La2Zr2O7 powders in pure pyrochlore structure were produced using this approach. Selected characteristics of the synthesized powders, such as crystal structure, lattice parameters, crystallite size, the vibrational properties, the morphology of the particles, along with the specific surface area and particle size have been investigated. The dependence of some properties on annealing temperatures of the powders has been studied.

Support Effects for Pt and Rh-Based Catalysts for Partial Oxidation of n-Tetradecane

Catalytic partial oxidation (CPOX) of liquid fuels is an attractive option for producing a hydrogen-rich gas stream for fuel cell applications. However, the high sulfur content along with aromatic compounds present in liquid fuels may deactivate reforming catalysts. Deactivation of these catalysts by carbon deposition and sulfur poisoning is a key technical challenge. The relationship between catalyst supports and deactivation have been studied here for three catalysts (Rh/Ce0.5 Zr0.5 O2 , Pt/Ce0.5 Zr0.5 O2 , and Pt/Al2 O3 ) in a fixed bed catalytic reactor using a mixture of n-tetradecane, 1-methylnaphthalene, and dibenzothiophene to simulate logistic fuels. Carbon production during CPOX reforming was directly related to olefin formation. Olefins, which are known coke precursors, were observed on the Pt catalysts during CPOX of n-tetradecane with no sulfur (particularly from Pt/Al2 O3 ), but not on Rh/Ce0.5 Zr0.5 O2 . For the Rh/Ce0.5 Zr0.5 O2 , yields of H2 and CO dropped to a stationary level after the introduction of sulfur-containing feed (1000 ppm sulfur) or aromatic-containing feed (5 wt%), however, the catalyst activity was restored after removing the sulfur or aromatics from the feed. For the Pt catalysts, H2 and CO yields dropped continuously over time in the presence of sulfur or aromatics in feed. The superior performance of Rh/Ce0.5 Zr0.5 O2 can be attributed to the higher oxygen-ion conductivity of the Ce0.5 Zr0.5 O2 support as well as the activity of the Rh sites.Copyright