Finding the optimum between volatility and cycle temperatures in solar thermochemical hydrogen production: Pb/PbO pair

A pilot unit for a concentrated solar thermal reactor with solar tracking was constructed. A 70 cm diameter concentrator dish could provide temperatures around 800 °C at a fairly steady rate. In the search for a redox pair that can work at such temperatures, studies were conducted on the feasibility of the Pb/PbO cycle for the splitting of H₂O for H₂ production. Thermodynamics accounting for the vapor pressures of Pb and PbO indicated favorable water splitting until approximately 900 °C, at atmospheric steam pressures. After 1000 °C, the vapor pressure of PbO becomes greater than that of Pb, as a result, thermodynamic favorability in the gas phase begins to be suppressed. The thermodynamic estimations were tested experimentally both in lab scale, and in bench scale molten bed reactors. The process went through similar maxima in the hydrogen production rates. The field tests in solar concentrator using a Pb coated mullite system did not reveal much due to evaporative loss of Pb and PbO under high solar flux. In this paper, it was demonstrated that the relatively high vapor pressure of Pb and PbO can be exploited for designing efficient water splitting cycles at temperatures <1000 °C using a PbO vapor recovery and circulation system.     

Effect of support and reduction temperature in the hydrogenation of CO2 over the Cu–Pd bimetallic catalyst with high Cu/Pd ratio

Metal-support interaction and catalyst pretreatment are important for industrial catalysis. This work investigated the effect of supports (SiO₂, CeO₂, TiO₂ and ZrO₂) for Cu–Pd catalyst with high Cu/Pd ratio (Cu/Pd = 33.5) regarding catalyst cost, and the reduction temperatures of 350 °C and 550 °C were compared. The activity based on catalyst weight follows the order of Si > Ce > Zr > Ti when reduced at 350 °C. The reduction temperature leads to the surface reconstruction over the SiO₂, CeO₂ and TiO₂ catalysts, while results in phase transition over Cu–Pd/ZrO₂. The effect of reduction temperature on catalytic performance is prominent for the SiO₂ and ZrO₂ supported catalysts but not for the CeO₂ and TiO₂ ones. Among the investigated catalysts, Zr-350 exhibits the highest methanol yield. This work reveals the importance of the supports and pretreatment conditions on the physical-chemical properties and the catalytic performance of the Cu–Pd bimetallic catalysts.     

Low-temperature catalytic conversion of greenhouse gases (CO2 and CH4) to syngas over ceria-magnesia mixed oxide supported nickel catalysts

Running dry reforming of methane (DRM) reaction at low-temperature is highly regarded to increase thermal efficiency. However, the process requires a robust catalyst that has a strong ability to activate both CH₄ and CO₂ as well as strong resistance against deactivation at the reaction conditions. Thus, this paper examines the prospect of DRM reaction at low temperature (400–600 °C) over CeO₂–MgO supported Nickel (Ni/CeO₂–MgO) catalysts. The catalysts were synthesized and characterized by XRD, N₂ adsorption/desorption, FE-SEM, H₂-TPR, and TPD-CO₂ methods. The results revealed that Ni/CeO₂–MgO catalysts possess suitable BET specific surface, pore volume, reducibility and basic sites, typical of heterogeneous catalysts required for DRM reaction. Remarkably, the activity of the catalysts at lower temperature reaction indicates the workability of the catalysts to activate both CH₄ and CO₂ at 400 °C. Increasing Ni loading and reaction temperature has gradually increased CH₄ conversion. 20 wt% Ni/CeO₂–MgO catalyst, CH₄ conversion reached 17% at 400 °C while at 900 °C it was 97.6% with considerable stability during the time on stream. Whereas, CO₂ conversions were 18.4% and 98.9% at 400 °C and 900 °C, respectively. Additionally, a higher CO₂ conversion was obtained over the catalysts with 15 wt% Ni content when the temperature was higher than 600 °C. This is because of the balance between a high number of Ni active sites and high basicity. The characterization of the used catalyst by TGA, FE-SEM and Raman Spectroscopy confirmed the presence of amorphous carbon at lower temperature reaction and carbon nanotubes at higher temperature.     

Deactivation and in-situ regeneration of Dy-doped Ni/SiO2 catalyst in CO2 reforming of methanol

The self-regeneration of Ni-based catalysts has been considered as a promising approach to maintain not only a continuous but also economical process. However, the effect of catalyst nature, operating temperature, amount and types of carbon deposits on the effectiveness of the in-situ regeneration is still not well-investigated. Therefore, in this work, the self-regeneration ability of the undoped and Dy-doped Ni/SiO₂ catalysts, which were prepared by the same impregnation method, were examined in the dry reforming of methanol. The physicochemical properties of the fresh and spent catalysts were analyzed by various techniques such as X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H₂-TPR), oxygen temperature-programmed desorption (O₂-TPD), transmission electron microscopy (TEM), N₂-BET isothermal adsorption. The nature and chemical reactivity of coke deposits formed during dry reforming at various temperatures (550, 600, and 650 °C) and the regeneration possibility of used catalysts through CO₂ gasification at these temperatures were investigated by the in-situ temperature-programmed gasification by CO₂ (TPCO₂). The Dy additive significantly improves the dispersion of the nickel active sites of Ni/SiO₂ catalyst, as demonstrated by the decreased Ni crystal size as well as the increased specific surface area and reduction degree of the catalyst. Furthermore, Dy promotion increases the quantity of oxygen vacancies and the nature of oxygen species, thereby improving the catalyst activity and stability. Specifically, methanol conversion dropped from 93% to 96%–61% and 31% for undoped Ni/SiO₂ at 600 °C and 650 °C, respectively and from about 99% to 87% (at 600 °C) and 52% (at 650 °C) for Dy-doped catalyst.     

Effect of Co,Fe and Rh addition on coke deposition over Ni/Ce0.5Zr0.5O2 catalysts for steam reforming of ethanol

Ni-based monometallic and bimetallic catalysts (Ni, NiRh, NiCo and NiFe) supported on Ce_0.5Zr_0.5O₂ support were evaluated on the steam reforming of ethanol (SRE) performance. The supports of Ce_0.5Zr_0.5O₂ composite oxide was prepared by co-precipitation method with Na₂CO₃ precipitant and assigned as CeZr(N). The monometallic catalyst was prepared by incipient wetness impregnation method and assigned as Ni/CeZr(N). The bimetallic catalysts were prepared by co-impregnation method to disperse the metals on the CeZr(N) support and assigned as NiM/CeZr(N). All samples were characterized by using XRD, TPR, BET, EA and TEM techniques at various stages of the catalyst. The results indicated that the facile reduction and smaller particle size of Ni/CeZr(N) (T₉₉ = 300 °C) and NiRh/CeZr(N) (T₉₉ = 250 °C) catalysts were preferential than the NiFe/CeZr(N) (T₉₉ = 325 °C) and NiCo/CeZr(N) (T₉₉ = 375 °C) catalysts. Also, both the Ni/CeZr(N) and NiRh/CeZr(N) catalysts displayed better durability among these catalysts over 100 h and 400 h, respectively. Since the serious coke formation for the NiCo/CeZr(N) catalyst, the activity only maintained around 6 h, the durability on the NiFe/CeZr(N) catalyst approached 50 h.     

Thermogravimetric analysis of coking during dry reforming of methane

Nickel-based catalysts used for dry reforming of methane (DRM) suffer from coking and sintering, which hinders the broad application of the process in the industry. Thermogravimetric analysis was employed to investigate coking on a commercial nickel catalyst with an anti-coking additive (CaO). It was found that the catalyst sintered at temperatures between 850 and 900 °C, which resulted in permanent catalyst deactivation. For the tested Ni/CaO–Al₂O₃ catalyst, the coking and carbon gasification rates are equal at the temperatures of 796–860 °C, depending on the heating rate (5–20 K/min). Significant differences in the temperatures related to the maxima on TG curves for various heating rates follow from DRM kinetics. This work reveals that the coking rate is lower at higher temperatures. After 50 min, the weight gains amount to about 20% and 40% at 800 °C and 600 °C, respectively. Lower sample weight gains were observed at higher temperatures for a methane decomposition reaction over the Ni/CaO catalyst, unlike for the second tested catalyst – activated carbon. For the nickel catalyst, the reaction order for methane decomposition is 0.6 in the temperature range 640–800 °C, while the sign of the activation energy changes at 700 °C. The elaborated kinetic equation predicts the initial CH₄ decomposition rate with 15% accuracy.     

Hydrogen production enhancement using hot gas cleaning system combined with prepared Ni-based catalyst in biomass gasification

This paper investigates the hot gas temperature effect on enhancing hydrogen generation and minimizing tar yield using zeolite and prepared Ni-based catalysts in rice straw gasification. Results obtained from this work have shown that increasing hot gas temperature and applying catalysts can enhance energy yield efficiency. When zeolite catalyst and hot gas temperature were adjusted from 250 °C to 400 °C, H₂ and CO increased slightly from 7.31% to 14.57%–8.03% and 17.34%, respectively. The tar removal efficiency varies in the 70%–90% range. When the zeolite was replaced with prepared Ni-based catalysts and hot gas cleaning (HGC) operated at 250 °C, H₂ contents were significantly increased from 6.63% to 12.24% resulting in decreasing the hydrocarbon (tar), and methane content. This implied that NiO could promote the water-gas shift reaction and CH₄ reforming reaction. Under other conditions in which the hot gas temperature was 400 °C, deactivated effects on prepared Ni-based catalyst were observed for inhibiting syngas and tar reduction in the HGC system. The prepared Ni-based catalyst worked at 250 °C demonstrate higher stability, catalyst activity, and less coke decomposition in dry reforming. In summary, the optimum catalytic performance in syngas production and tar elimination was achieved when the catalytic temperature was 250 °C in the presence of prepared Ni-based catalysts, producing 5.92 MJ/kg of lower heating value (LHV) and 73.9% tar removal efficiency.     

Hydrogen production from sodium borohydride originated compounds: Fabrication of electrospun nano-crystalline Co3O4 catalyst and its activity

Electrospun nanofibers are prepared through electrospinning followed by post-treatment and preferred to use in catalytic applications. The electrospinning provides advantages for active catalysts design based on activity profiles and features of catalyst. In the present study, we fabricated nano-crystalline cobalt oxide (Co₃O₄) catalyst by electrospinning technique followed by thermal conditioning. Polyacrylonitrile (PAN) based Co as-spun mats (Co/NMs) with homogeneous diameter were prepared by electrospinnig process under several conditions as applied voltage (15–25 kV), working distance (5–7.5 cm) with the feed rate of 1 ml min⁻¹. The calcination process as a post-treatment was applied at different temperatures (232 °C, 289 °C and 450 °C) to obtain electrospun nano-crystalline Co₃O₄ catalyst. Co/NMs catalysts were characterized by XRD, SEM, TEM, XPS, FT-IR, TG/DTG, and ICP-MS techniques. The parametrically study was performed for evaluating the hydrogen production activity of catalyst from sodium borohydride (NaBH₄, SBH) and its originated compounds as ammonia borane (NH₃BH₃, AB) and methyl-amine borane (CH₃NH₂BH₃, MeAB). The relation between the internal-external properties and catalytic activities of catalysts for hydrogen production was investigated. The beadless Co/NMs-1 catalyst with homogeneous diameter was obtained under electrospinnig process conditions at 15 kV applied voltage and 7.5 cm working distance. All catalysts showed activity for hydrogen production, also the significant effect of post treatment process was observed on the catalytic activity as given order: Co/NMs-1₄₅₀ > Co/NMs-1₂₈₉ > Co/NMs-1 > Co/NMs-1₂₃₂. Furthermore, mesoporous Co₃O₄ cubic crystals (26 nm) in fibrous architecture was prepared by 450 °C-post-treatment. Hydrogen production rates were recorded at 60 °C as 2.08, 2.20, and 6.39 l H₂.g_cat⁻¹min⁻¹ for NaBH₄, CH₃NH₂BH₃, and NH₃BH₃, respectively.     

Hydrogen-rich syngas production by catalytic cracking of tar in wastewater under supercritical condition

This paper presents the results from experimental study of syngas production by catalytic cracking of tar in wastewater under supercritical condition. Ni/Al₂O₃ catalysts were prepared via the ultrasonic assisted incipient wetness impregnation on activated alumina, and calcined at 600 °C for 4 h. All catalysts showed mesoporous structure with specific surface area in a range of 146.6–215.3 m²/g. The effect of Ni loading (5–30 wt%), reaction temperature (400–500 °C), and tar concentration (0.5–7 wt%) were systematically investigated. The overall reaction efficiency and the gas yields, especially for H₂, were significantly enhanced with an addition of Ni/Al₂O₃ catalysts. With 20%Ni/Al₂O₃, the H₂ yield increased by 146% compared to the non-catalytic experiment. It is noteworthy that the reaction at 450 °C with the addition of 20%Ni/Al₂O₃ had a comparable efficiency to the reaction without catalyst at 500 °C. The maximum H₂ yield of 46.8 mol/kg_tar was achieved with 20%Ni/Al₂O₃ at 500 °C and 0.5 wt% tar concentration. The catalytic performance of the catalysts gradually decreased as the reuse cycle increased, and could be recovered to 88% of the fresh catalyst after regeneration. 20%Ni/Al₂O₃ has a potential to improve H₂ production, as well as a good reusability. Thus, it is considered a promising catalyst for energy conversion of tar in wastewater.     

Selective hydrogen combustion in the presence of propylene and propane over Pt/A-zeolite catalysts

The behavior of selective hydrogen combustion (SHC) in the presence of propylene and propane changing with reaction temperature in a range of 100–600 °C has been investigated over the Pt catalysts supported on A-zeolites. The effect of Pt loading varying from 0.01 to 2 wt% on the catalytic SHC performance has been studied in the conditions with a feed gas molar composition of C₃H₈/C₃H₆/H₂/O₂ = 4/4/4/2 balanced with N₂ and gas hourly space velocity of 15,000 h⁻¹. The results show that for each Pt/3A catalyst having a different Pt loading there is a maximum of H₂ conversion by combustion appearing between 300 and 400 °C, while the selectivity to comprehensive H₂ conversion can maintain 100% when the temperature lower than 300 °C. Moreover, the Pt/3A catalyst with a Pt loading of 0.5 wt % performs better than the others at the temperatures higher than 300 °C. The maximal H₂ combustion achieved over the 0.5 wt% Pt/3A catalyst is as high as 96.6% along with a selectivity of 100% at 300 °C, and a 92.4% H₂ combustion with 98.5% selectivity can be obtained even if at 500 °C. The characterization of the catalysts reveals that the distribution of Pt atoms and the number of atoms in Pt clusters may be the key factors for giving rise to the good SHC performance. The influence of three types of A-zeolite supports on the Pt catalyzed SHC process has also been investigated. 3A zeolite is superior to 4A and 5A for supporting 0.5 wt% Pt catalyst in terms of both activity and selectivity. The lower C₃H₆ conversion on the 0.5 wt% Pt/3A catalyst compared to the 0.5 wt% Pt/5A may be ascribed to the insufficient sites for the C₃H₆ activation on the surface of Pt/3A due to the limitation of 3A channels inaccessible to C₃H_6. This contrarily brings about the better SHC performance on the 0.5 wt% Pt/3A catalyst.     

Comparison of microwave and conventionally heated reactor performances in catalytic dehydrogenation of ethane

In the present study, non-oxidative dehydrogenation of ethane was carried out by using conventional heated (CHRS) and microwave heated (MWHRS) reactor systems. Reactions were conducted in the presence of SBA-15 supported Cr or Mo catalysts, and the activity of the catalysts were evaluated in terms of ethane conversion and C₂H₄/H₂ ratio. The physicochemical properties of synthesized catalysts were determined by XRD, N₂ adsorption/desorption, ICP-OES, TPR, SEM, and EDS analysis. XRD pattern of reduced catalysts revealed the formation of metallic Mo and Eskolaite Cr₂O₃ over the catalysts. The mesoporous structure of SBA-15 was confirmed using N₂ adsorption/desorption analysis. Activity test results showed higher ethane conversion in the presence of Mo than Cr in both reactor systems. However, more side reaction took place over Mo than Cr based catalysts. Cr based catalyst showed better activity in terms of ethylene formation and C₂H₄/H₂ ratio. Results proved the superior performance of microwave heated reactor over the conventionally heated reactor. Significantly higher conversion was obtained over Cr based catalysts in MWHRS than CHRS due to the occurrence of micro-plasmas (hot spots) in the catalyst bed. The performance of 5Cr@SBA-15 in CHRS was poor due to negligible ethane conversion below 650 °C, while almost complete conversion could be achieved in MWHRS with this catalyst at identical conditions. The ethane conversion values obtained at 650 °C in CHRS were achieved at 450 °C, in MWHRS.     

Determining most effective structural form of nickel-cobalt catalysts for dry reforming of methane

In this study, catalytic activity of carbon dioxide reforming of methane was investigated over nickel-cobalt catalysts in various structural forms. Catalytic activity tests were performed at the temperatures of 600–800 °C in a micro-flow quartz reactor. SEM-EDX, XRD and XPS studies were also performed to understand the surface morphology of the catalysts. The results showed that 8 wt%Ni-2wt.%Co on wash-coated MgO over monolithic structure led to highest catalytic performances with CH₄ and CO₂ conversions of 83% and 89% respectively as well as H₂/CO ratio of 0.95 at 750 °C. SEM-EDX and XPS results of catalyst spent at 750 °C also showed considerable amount of coke formation; however, the use of 3% oxygen in the feed suppressed the coke formation significantly. The catalyst was stable for 48 h in the presence of O₂ (3%) added feed at the temperature of 750 °C.     

Comparison of hydrogen consumption behavior of chromium and manganese promoted copper-based catalysts

CuO/ZnO/Al₂O₃/MgO–Cr and -Mn catalysts are synthesized using nitrate route via co-precipitation method. The precursors are characterized by XRD. The decomposition behavior of the precursors is analyzed by Air-TGA. The catalysts calcined at 250, 300, 350 and 450 °C are characterized by XRD and BET. CuO particle size reduction and surface area of the catalysts are investigated. Increasing the calcination temperature from 350 °C to 450 °C crystallite size increases about 3 nm, and BET surface area decreases about 30 m²/g. The reduction characteristics of the catalysts are analyzed via TPR and H₂-TGA, and H₂ consumption values of Cr and Mn containing catalysts is found as 40% and 60%, respectively. Peak temperatures of Mn containing catalysts (290–325 °C) are lower than peak temperatures of Cr containing catalysts (300–360 °C) as confirmed by H₂-TGA and H₂-DTG. The optimum H₂ consumption value of 52% is obtained with CuO/ZnO/Al₂O₃/MgO–Mn catalyst calcined at 350 °C.     

Monoliths washcoated with AuCu catalysts for CO removal in an ethanol fuel processor: Effect of CeO2–SiO2 dual support on the catalytic performance and reactor cost

CO removal from a syngas was evaluated in a single catalytic unit using structured AuCu/CeO₂–SiO₂ catalysts. Initially, AuCu/CeO₂–SiO₂ powder catalysts with several SiO₂ loadings (0–100 mol%) were assessed. SiO₂ addition into AuCu/CeO₂ increased the surface area by up to 3.4 times and reduced its cost by up to 60%, but reduced CO conversion. On the other hand, the AuCu/CeO₂–SiO₂ catalyst washcoated on monolith outperformed the powder samples at temperatures above 260 °C. In particular, outlet CO concentrations adequate to feed high temperature fuel cells were obtained with monoliths washcoated with AuCu/CeO₂ (0.2% CO) and AuCu/CeO₂–SiO₂ with 75 mol% of SiO₂ (3.6% CO). Furthermore, the Au/CeO₂–SiO₂ monolith (14 $/g_cat) is 36% cheaper than the AuCu/CeO₂ monolith, paving the road to the development of compact and economic H₂ cleanup processes.     

Combined pre-reformer/reformer system utilizing monolith catalysts for hydrogen production

The pre-reforming of higher hydrocarbon, propane, was performed to generate hydrogen from LPG without carbon deposition on the catalysts. A Ru/Ni/MgAl₂O₄ metallic monolith catalyst was employed to minimize the pressure drop over the catalyst bed. The propane pre-reforming reaction conditions for the complete conversion of propane with no carbon formation were identified to be the following: space velocities over 2400 h⁻¹ and temperatures between 400 and 450 °C with a H₂O/C₁ ratio of 3. The combined pre-reformer and the main reformer system with the Ru/Ni/MgAl₂O₄ metallic monolith catalyst was employed to test the conversion propane to syngas where the reaction heat was provided by catalytic combustors. Propane was converted in the pre-reformer to 52.5% H₂, 27.0% CH₄, 17.5% CO, and 3.0% CO₂ with a 331 °C inlet temperature and a 482 °C catalyst outlet temperature. The main steam reforming reactor converted the methane from the pre-reformer with a conversion of higher than 99.0% with a 366 °C inlet temperature and an 824 °C catalyst outlet temperature. With a total of 912 cc of the Ru/Ni/MgAl₂O₄ metallic monolith catalyst in the main reformer, the H₂ production from the propane reached an average of 3.25 Nm³h⁻¹ when the propane was fed at 0.4 Nm³h⁻¹.     

Solid-state synthesis method for the preparation of cobalt doped Ni–Al2O3 mesoporous catalysts for CO2 methanation

In this study, a simple solid-state synthesis method was employed for the preparation of the Ni–Co–Al₂O₃ catalysts with various Co loadings, and the prepared catalysts were used in CO₂ methanation reaction. The results demonstrated that the incorporation of cobalt in nickel-based catalysts enhanced the activity of the catalyst. The results showed that the 15 wt%Ni-12.5 wt%Co–Al₂O₃ sample with a specific surface area of 129.96 m²/g possessed the highest catalytic performance in CO₂ methanation (76.2% CO₂ conversion and 96.39% CH₄ selectivity at 400 °C) and this catalyst presented high stability over 10 h time-on-stream. Also, CO methanation was investigated and the results showed a complete CO conversion at 300 °C.     

Design,simulation and experimental study of a directly-irradiated solar chemical reactor for hydrogen and syngas production from continuous solar-driven wood biomass gasification

The use of concentrated solar energy as the high-temperature heat source for the thermochemical gasification of biomass is a promising prospect for producing CO₂-neutral chemical fuels (syngas). The solar process saves biomass resource because partial combustion of the feedstock is avoided, it increases the energy conversion efficiency because the calorific value of the feedstock is upgraded by the solar power input, and it also reduces the need for downstream gas cleaning and separation because the gas products are not contaminated by combustion by-products. A new concept of solar spouted bed reactor with continuous biomass injection was designed in order to enhance heat transfer in the reactor, to improve the gasification rates and gas yields by providing constant stirring of the particles, and to enable continuous operation. Thermal simulations of the prototype were performed to calculate temperature distributions and validate the reactor design at 1.5 kW scale. The reliable operation of the solar reactor based on this new design was also experimentally demonstrated under real solar irradiation using a parabolic dish concentrator. Wood particles were continuously gasified at temperatures ranging from 1100 °C to 1300 °C using either CO₂ or steam as oxidizing agent. Carbon conversion rates over 94% and gas productions over 70 mmol/g_biomass were achieved. The energy contained in the biomass was upgraded thanks to the solar energy input by a factor of up to 1.21.     

Nano-sized RuO2 electrocatalyst improves the electrochemical performance for hydrogen oxidation reaction

Hydrogen oxidation reaction (HOR) can be applied to proton exchange membrane fuel cells to generate electrical energy and anode discharge. Due to its special properties, RuO₂ has been applied to supercapacitors, phenolic wastewater, textile industry wastewater, and degrading organic substances. However, there is few reports on the application of the RuO₂ catalyst to hydrogen oxidation reaction (HOR). In this study, we successfully obtained RuO₂ NPs using a simple and eco-friendly hydrothermal method. Furthermore, the electrochemical activity of RuO₂ NPs prepared at different concentration (0.15 M, 0.20 M) and different hydrothermal temperature (150 °C, 160 °C, and 170 °C) was evaluated by the hydrogen oxidation reaction. The particle size, composition, dispersion and morphology of the obtained RuO₂ catalysts were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). In addition, cyclic voltammograms (CV) were utilized to investigate the electrochemical activity of the RuO₂ catalysts. The results showed that the obtained catalyst at a hydrothermal temperature of 160 °C and a concentration of 0.15 M displayed a Brunauer-Emmett-Teller (BET) surface area of 26.74 m² g⁻¹. Meanwhile, the catalyst had a uniform distribution. The hydrogen oxidation current density of the obtained RuO₂ catalysts is upto 6 mA cm⁻², showing a good electrochemical activity for hydrogen oxidation reaction.     

Powder and structured Pt/Ce0.75Zr0.25O2-based catalysts: Water gas shift performance and quasi in situ XPS studies

The data on the performance in water gas shift reaction of a powder 5 wt% Pt/Ce_0.75Zr_0.25O₂ and a structured 0.33 wt% Pt/Ce_0.75Zr_0.25O₂/θ-Al₂O₃/FeCrAl catalysts are reported in this work. For the powder one the lowest outlet CO concentrations were shown to be 0.5, 0.9 and 1.5 vol% corresponding to the initial ones of 5, 10 and 15 vol%, respectively; the temperature required to reach these values did not exceed 310 °C. The quasi in situ XPS data have shown that doping CeO₂ with Zr enhances the reducibility of the oxide allowing Ce³⁺ formation without any treatment. Additionally, it was found that there are 20–30% of nonmetallic Pt atoms on the surface even after a treatment in CO at 300 °C. For the structured catalyst the downward temperature gradient along the monolith was observed with a dispersion of 50–60 °C. The lowest CO concentrations were observed at the temperatures at the catalyst's back point of 280 °C–3.9 and 4.3 vol% CO in the dry gas for 15,700 and 31,400 cm³·g_cat⁻¹·h⁻¹, respectively, for 10 vol% CO in the feed gas.     

Zirconia supported nickel catalysts for glycerol steam reforming: Effect of zirconia structure on the catalytic performance

The effect of the zirconia structure in Ni/ZrO₂ catalysts on the glycerol steam reforming (GSR) reaction was studied. A tetragonal zirconia support was synthesized via a hydrolysis technique and loaded with 5 wt% Ni via a wet-impregnation method. Similarly, a commercial monoclinic zirconia support was also impregnated with 5 wt% Ni. Following calcination at 600 °C, physico-chemical properties of the prepared catalysts were investigated by X-Ray Diffraction (XRD), H₂-Temperature Programmed Reduction (H₂-TPR) and CO₂-Temperature Programmed Desorption (CO₂-TPD) techniques. The catalysts were then tested in the GSR reaction in the 400–700 °C range with a steam to glycerol molar ratio of 9:1 and a flow rate of 0.025 mL/min. The monoclinic catalyst exhibited a better performance giving higher hydrogen yields and glycerol conversions. This was attributed to an improved reducibility of Ni in this catalyst. Stability tests at 600 °C revealed the deactivation of the tetragonal catalyst during 6 h as a result of the formation of encapsulating coke which blocked active Ni metal sites. The monoclinic catalyst, exhibiting the formation of only filamentous coke, remained relatively stable for 24 h.