Promoting the Selectivity of Pt/m-ZrO2 Ethanol Steam Reforming Catalysts with K and Rb Dopants

The ethanol steam reforming reaction (ESR) was investigated on unpromoted and potassium- and rubidium-promoted monoclinic zirconia-supported platinum (Pt/m-ZrO2) catalysts. Evidence from in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) characterization indicates that ethanol dissociates to ethoxy species, which undergo oxidative dehydrogenation to acetate followed by acetate decomposition. The acetate decomposition pathway depends on catalyst composition. The decarboxylation pathway tends to produce higher overall hydrogen selectivity and is the most favored route at high alkali loading (2.55 wt.% K and higher or 4.25 wt.% Rb and higher). On the other hand, decarbonylation is a significant route for the undoped catalyst or when a low alkali loading (e.g., 0.85% K or 0.93% Rb) is used, thus lowering the overall H2 selectivity of the process. Results of in situ DRIFTS and the temperature-programmed reaction of ESR show that alkali doping promotes forward acetate decomposition while exposed metallic sites tend to facilitate decarbonylation. In previous work, 1.8 wt.% Na was found to hinder decarbonylation completely. Due to the fact that 1.8 wt.% Na is atomically equivalent to 3.1 wt.% K and 6.7 wt.% Rb, the results show that less K (2.55% K) or Rb (4.25% Rb) is needed to suppress decarbonylation; that is, more basic cations are more efficient promoters for improving the overall hydrogen selectivity of the ESR process.

Sustainable Production of Hydrogen by Steam Reforming of Ethanol Using Cobalt Supported on Nanoporous Zeolitic Material

Cobalt catalysts supported on Y zeolite and mesoporized Y zeolite (Y-mod) have been studied in steam reforming of ethanol (SRE). Specifically, the effect of the mesoporosity and the acidity of the y zeolite as a support has been explored. Mesoporous were generated on Y zeolite by treatment with NH4F and the acidity was neutralized by Na incorporation. Four cobalt catalysts supported on Y zeolite have been prepared, two using Y zeolite without mesoporous (Co/Y, Co/Y-Na), and two using Y zeolite with mesoporous (Co/Y-mod and Co/Y-mod-Na). All catalysts showed a high activity, with ethanol conversion values close to 100%. The main differences were found in the distribution of the reaction products. Co/Y and Co/Y-mod catalysts showed high selectivity to ethylene and low hydrogen production, which was explained by their high acidity. On the contrary, neutralization of the acid sites could explain the higher hydrogen selectivity and the lower ethylene yields exhibited by the Co/Y-Na and Co/Y-mod-Na. In addition, the physicochemical characterization of these catalysts by XRD, BET surface area, temperature-programmed reduction (TPR), and TEM allowed to connect the presence of mesoporous with the formation of metallic cobalt particles with small size, high dispersion, and with high interaction with the zeolitic support, explaining the high reforming activity exhibited by the co/y-mod-Na sample as well as its higher hydrogen selectivity. It has been also observed that the formation of coke is affected by the presence of mesoporous and acidity. Both properties seem to have an opposite effect on the reforming catalyst, decreasing and increasing the coke deposition, respectively.

Compact Heat Integrated Reactor System of Steam Reformer, Shift Reactor and Combustor for Hydrogen Production from Ethanol

A compact heat integrated reactor system (CHIRS) of a steam reformer, a water gas shift reactor, and a combustor were designed for stationary hydrogen production from ethanol. Different reactor integration concepts were firstly studied using Aspen Plus. The sequential steam reformer and shift reactor (SRSR) was considered as a conventional system. The efficiency of the SRSR could be improved by more than 12% by splitting water addition to the shift reactor (SRSR-WS). Two compact heat integrated reactor systems (CHIRS) were proposed and simulated by using COMSOL Multiphysics software. Although the overall efficiency of the CHIRS was quite a bit lower than the SRSR-WS, the compact systems were properly designed for portable use. CHIRS (I) design, combining the reactors in a radial direction, was large in reactor volume and provided poor temperature control. As a result, the ethanol steam reforming and water gas shift reactions were suppressed, leading to lower hydrogen selectivity. On the other hand, CHIRS (II) design, combining the process in a vertical direction, provided better temperature control. The reactions performed efficiently, resulting in higher hydrogen selectivity. Therefore, the high performance CHIRS (II) design is recommended as a suitable stationary system for hydrogen production from ethanol.

Air Gasification of Banana (Musa spp.) Residues to Produce Biofuels

Thermochemical conversion of biomass is a technique used in recovering its energetic content and for the production useful biofuels. A lot of wastes/residues are generated from the harvesting and consumption of banana fruits. This study developed an ASPEN Plus model for the gasification of banana (Musa Spp.) residues pseudo-stem, the peels and the leaves. The model will be used to study the effect of gasification temperature, gasification pressure and air-fuel ratio (AFR) on the selectivity of the chemical species in the product stream. For all three residues, the selectivity of hydrogen increases with temperature with temperature. At the optimum temperature, the hydrogen molar selectivity in the product stream is 56% (900oC), 55% (900oC) and 53% (700oC) for pseudo-stem, peels and leaves respectively. At the optimum atmospheric pressure, the hydrogen molar percentage in the product stream was 48%, 49% and 50% for pseudo-stem, peels and leaves respectively. At the optimum AFR, the hydrogen selectivity in the product stream is 55%, 52% and 46% for pseudo-stem, peels and leaves respectively. All three residues are reasonably good feedstock for the gasification process but the pseudo-stem possesses a marginal advantage over the others.

Hydrogen Production from Ethanol Steam Reforming Using Ce- and La- Modified Mesoporous MCM-41 Supported Nickel-Based Catalysts

Mesoporous MCM-41 containing different amounts of nickel (10, 15 and 20 wt%) and Ce and/or La promoters were prepared by hydrothermal and wet-impregnation methods. The catalysts were characterized by means of temperature-programmed reduction (TPR), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), N2 adsorption-desorption, Fourier transform infrared (FT-IR) spectroscopy, and thermogravimetric (TGA) analyses. Then, the catalysts were tested for hydrogen production via steam reforming of ethanol in a fixed bed reactor. Hydrogen selectivity and ethanol conversion over Ni/MCM-41 catalyst were 69.6 % and 94 %, respectively. The best catalytic results were obtained with Ce-Ni/MCM-41 catalyst, i. e. 94 % ethanol conversion and 76.5 % hydrogen selectivity. These results remained constant about 90 h time on stream and ethanol conversion decreased to 87 % after 120 h.

Hydrogen generation from the decomposition of hydrous hydrazine using amorphous NiB nanocatalysts prepared by chemical etching method

Hydrous hydrazine (N2H[Formula: see text]O) is considered to be one of the most promising chemicals for hydrogen storage, and the development of high-efficient and noble-metal-free catalysts is of key importance for N2H[Formula: see text]O decomposition to generate hydrogen. In this work, NiZnB nanoparticles (NiZnB NPs) synthesized by co-reduction method were further treated to remove the metal zinc by chemical etching with sodium hydroxide, and the resulting amorphous NiB nanocatalysts (NiB NCs) presented higher specific surface area and hydrogen selectivity than that of common NiB nanoparticles. Experimental results also indicate that heat-treatment of the NiZnB NPs can increase turnover frequency (TOF) but decrease hydrogen selectivity of the NiB NCs. NiB NCs derived from NiZnB NPs heated at 200[Formula: see text]C show TOF and selectivity of 0.72[Formula: see text]h[Formula: see text] and 98.1%, respectively. In addition, reusability of the resulting catalyst was also investigated.

Catalytic Performance and Characterization of Ni-Co Bi-Metallic Catalysts in n-Decane Steam Reforming: Effects of Co Addition

Co-Ni bi-metallic catalysts supported on Ce-Al2O3 (CA) were prepared with different Co ratios, and the catalytic behaviors were assessed in the n-decane steam reforming reaction with the purpose of obtaining high H2 yield with lower inactivation by carbon deposition. Physicochemical characteristics studies, involving N2 adsorption-desorption, X-ray diffraction (XRD), H2-temperature-programmed reduction (H2-TPR), NH3 temperature programmed reduction (NH3-TPD), SEM-energy dispersive spectrometer (EDS), and transmission electron microscope (TEM)/HRTEM, were performed to reveal the textural, structural and morphological properties of the catalysts. Activity test indicated that the addition of moderate Co can improve the hydrogen selectivity and anti-coking ability compared with the mono-Ni/Ce-Al2O3 contrast catalyst. In addition, 12% Co showed the best catalytic activity in the series Co-Ni/Ce-Al2O3 catalysts. The results of catalysts characterizations of XRD and N2 adsorption-desorption manifesting the metal-support interactions were significantly enhanced, and there was obvious synergistic effect between Ni and Co. Moreover, the introduction of 12% Co and 6% Ni did not exceed the monolayer saturation capacity of the Ce-Al2O3 support. Finally, 6 h stability test for the optimal catalyst 12%Co-Ni/Ce-Al2O3 demonstrated that the catalyst has good long-term stability to provide high hydrogen selectivity, as well as good resistance to coke deposition.