Rapid evaluation of coke resistance in catalysts for methane reforming using low steam-to-carbon ratio

Egg-Shell-Type MgAl2O4 Pellet Catalyst for Steam Methane Reforming Reaction Activity: Effect of Pellet Preparation Temperature

A pellet catalyst was prepared to be used in a large-scale steam methane reformer. Hydrotalcite powder (MG30) was used as a precursor to prepare MgAl2O4 pellet supports at different calcination temperatures. Ni-supported catalysts with egg-shell-type distribution were prepared on these pellet supports: Ni/sup-x (where x is the calcination temperature of the support with x = 1273, 1373, and 1473 K). Among them, Ni/sup-1473, which experienced the highest calcination temperature (1473 K), showed the highest methane conversion and lowest weight loss owing to carbon deposition. As a result, when the calcination temperature increased, the egg-shell thickness decreased, and the reducibility of the catalyst was enhanced. Although a small amount of Ni (3.5 wt%) was used, the egg-shell-type catalyst had superior catalytic activity and coke resistance. Therefore, the egg-shell-type catalyst using Ni as the active material and MgAl2O4 calcined at high temperature as the support is expected to be appropriate for large-scale industrial steam methane reforming reactions.

Nanowire-Based Materials as Coke-Resistant Catalyst Supports for Dry Methane Reforming

In this paper, nanowire-supported catalysts loaded with nickel are shown to be coke resistant compared to nanoparticle-supported catalysts. Specifically, Ni-loaded titania-based nanowire catalysts were tested with the dry methane reforming process in a laboratory-scale continuous packed-bed atmospheric reactor. The CO2 conversion rate stayed above 90% for over 30 h on stream under coke-promoting conditions, such as high flow rates, low temperatures, and a high ratio of CH4 to CO2. The coke (CxHy, x>>y) on the spent catalyst surface for both nanowire- and nanoparticle-supported catalysts was characterized by TGA, temperature-programmed reduction (TPR), and electron microscopy (SEM/TEM/EDS), and it was revealed that the types of carbon species present and their distribution over the morphology-enhanced materials played a major role in the deactivation. The CO2 conversion activity of Ni supported on titania nanoparticles was reduced from ~80% to less than 72% in 30 h due to the formation of a graphitic coke formation. On the other hand, Ni particles supported on nanowires exhibited cube-octahedral morphologies, with a high density of non- (111) surface sites responsible for the increased activity and reduced graphitic coke deposition, giving a sustained and stable catalytic activity during a long time-on-stream experiment.

Steam Reforming of Model Bio-Oil Aqueous Fraction Using Ni-(Cu, Co, Cr)/SBA-15 Catalysts

Hydrogen obtained from biomass derivatives is considered a promising alternative to fossil fuels. The aim of this work is to test the viability of Ni-M/SBA-15 (M: Co, Cu, Cr) catalysts for the hydrogen production from bio-oil aqueous fraction reforming. Tests were performed in a fixed-bed reactor at 600 °C and atmospheric pressure. Firstly, the steam reforming (SR) of acetic acid, hydroxyacetone, furfural and phenol, as representative constituents of the bio-oil aqueous fraction, was carried out. Lower reactivity with increasing carbon number and decreasing steam-to-carbon ratio was observed. Coking rate during SR is a consequence of carbon number and aromaticity of the reactant, as well as the steam-to-carbon ratio. However, deactivation also depends on the graphitization degree of carbon filaments, higher in the case of coke formed from phenol. Then, the performance of the Ni-M/SBA-15 catalysts was studied in the reforming of a bio-oil aqueous fraction surrogate containing the four model compounds. Ni-Co/SBA-15 and Ni-Cr/SBA-15 samples were the most active because Co also catalyze the steam reforming reactions and Cr promotes the formation of very small Ni crystallites accounting for high conversion and the low coke deposition (~8 times lower than Ni/SBA-15) in the form of poorly condensed carbon filaments.

Dry Reforming of Methane in a Pd-Ag Membrane Reactor: Thermodynamic and Experimental Analysis

The present work is a study of CO2 Reforming of Methane (DRM) carried out in a catalytic Pd-based membrane reactor. A detailed thermodynamic analysis is carried out, calculating the chemical equilibrium parameters in two different cases: (a) DRM along with the Reverse Water Gas Shift (RWGS) reaction and (b) DRM along with both RWGS and the Boudouard Reaction (BR). The performance of membrane reactor is then experimentally analyzed in terms of methane conversion, hydrogen recovery and H2/CO reaction selectivity by varying feed pressure and CO2/CH4 feed molar ratio and 500 °C and GHSV = 100 h−1. Among the obtained results, a CH4 conversion of about 26% and a H2 recovery of 47% are achieved at low feed pressures, exceeding the traditional reactor equilibrium conversion. This effect can be attributed to the favorable thermodynamics coupled to the hydrogen permeation through the membrane. This study further demonstrates the general effectiveness of membrane-integrated reaction processes, which makes the production of syngas more efficient and performing, providing important environmental benefits.