Equilibrium potassium coverage and its effect on a Ni tar reforming catalyst in alkali- and sulfur-laden biomass gasification gases

Moud, Pouya H.; Andersson, Klas; Lanza, Roberto; Engvall, Klas

doi:10.1016/j.apcatb.2016.03.007

Cited by 40 publications

(24 citation statements)

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“…2 Nickel-based catalysts are commonly used in industry for catalytic steam reforming of fossil hydrocarbon feedstock, and are also foreseen as technically and economically feasible in biomass gasification. 3 Albeit in use for long time in fossil feedstock steam reforming, the complexity of the biomass tar and presence of impurities remains a challenge for understanding the catalytic processes, as previously shown by Moud et al 4 Naphthalene is typically present in the biomass gasification gas and has been identified as one of the most difficult molecules to decompose, 2 and therefore frequently used as a model molecule for catalyst activity testing and design. Since naphthalene is also an intermediate in the decomposition mechanisms of higher poly aromatic hydrocarbons to syngas molecules, 3 it is in this perspective important to understand the elementary steps of its transformation such as primary adsorption and dehydrogenation, as well as possible surface carbon passivation mechanisms, caused by naphthalene.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Nickel-based catalysts are commonly used in industry for catalytic steam reforming of fossil hydrocarbon feedstock, and are also foreseen as technically and economically feasible in biomass gasification . Albeit in use for long time in fossil feedstock steam reforming, the complexity of the biomass tar and presence of impurities remains a challenge for understanding the catalytic processes, as previously shown by Moud et al…”

Section: Introductionmentioning

confidence: 99%

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Naphthalene on Ni(111): Experimental and Theoretical Insights into Adsorption, Dehydrogenation, and Carbon Passivation

et al. 2017

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An attractive solution to mitigate tars and also to decompose lighter hydrocarbons in biomass gasification is secondary catalytic reforming, converting hydrocarbons to useful permanent gases. Albeit that it has been in use for a long time in fossil feedstock catalytic steam reforming, understanding of the catalytic processes is still limited. Naphthalene is typically present in the biomass gasification gas and to further understand the elementary steps of naphthalene transformation, we investigated the temperature dependent naphthalene adsorption, dehydrogenation and passivation on Ni(111). TPD (temperature-programmed desorption) and STM (scanning tunneling microscopy) in ultrahigh vacuum environment from 110 K up to 780 K, combined with DFT (density functional theory) were used in the study. Room temperature adsorption results in a flat naphthalene monolayer. DFT favors the dibridge[7] geometry but the potential energy surface is rather smooth and other adsorption geometries may coexist. DFT also reveals a pronounced dearomatization and charge transfer from the adsorbed molecule into the nickel surface. Dehydrogenation occurs in two steps, with two desorption peaks at approximately 450 and 600 K. The first step is due to partial dehydrogenation generating active hydrocarbon species that at higher temperatures migrates over the surface forming graphene. The graphene formation is accompanied by desorption of hydrogen in the high temperature TPD peak. The formation of graphene effectively passivates the surface both for hydrogen adsorption and naphthalene dissociation. In conclusion, the obtained results on the model naphthalene and Ni(111) system, provides insight into elementary steps of naphthalene adsorption, dehydrogenation, and carbon passivation, which may serve as a good starting point for rational design, development and optimization of the Ni catalyst surface, as well as process conditions, for the aromatic hydrocarbon reforming process.

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Section: ■ Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Naphthalene on Ni(111): Experimental and Theoretical Insights into Adsorption, Dehydrogenation, and Carbon Passivation

et al. 2017

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“…In our previous studies, we first developed and implemented a methodology enabling controlled investigation of the influence of gas-phase alkali on a tar reforming Ni/MgAl 2 O 4 catalyst activity under realistic steady-state conditions by eliminating transient effects, caused by sulfur poisoning and sintering and by tailoring the S surface coverage by adjusting the H 2 S/H 2 ratio . The methodology was further applied in a study investigating the combined effects of biomass-derived gas-phase potassium at varying concentrations together with sulfur on tar reforming catalyst performance . In summary, these studies provided information concerning the equilibrium K coverage on a typical Ni-based steam reforming catalyst under tar reforming conditions.…”

Section: Introductionmentioning

confidence: 99%

Gas-Phase Potassium Effects and the Role of the Support on the Tar Reforming of Biomass-Derived Producer Gas Over Sulfur-Equilibrated Ni/MgAl₂O₄

et al. 2020

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Biomass gasification is a sustainable way to convert biomass residues into valuable fuels and chemicals via syngas production. However, several gas impurities need to be removed before the final synthesis. Understanding of the interactions and effects of biomass-derived producer gas contaminants (S and K) on the performance of reforming catalysts is of great importance when it comes to process reliability and development. In the present study, the steam reforming activity at 800 °C of a sulfur-equilibrated nickel catalyst during controlled exposure to alkali species (∼2 ppmv K) and in its absence was investigated using real producer gas from a 5 kWth O2-blown fluidized-bed gasifier. Conversions of CH4, C2H4, and C10H8 were used to evaluate the performance of the Ni/MgAl2O4 catalyst and MgAl2O4 support. A significant and positive effect on the catalyst activity is observed with addition of gas-phase KCl. This is assigned primarily to the observed K-induced reduction in sulfur coverage (θS) on Nian effect which is reversible. The catalytic contribution of the K-modified pure MgAl2O4 support was found to be significant in the conversion of naphthalene but not for light hydrocarbons. The product and catalyst analyses provided evidence to elucidate the preferential adsorption site for S and K on the catalyst as well as the role of the support. Whereas S, as expected, was found to preferentially adsorb on the surface of Ni particles, forming S-Ni sites, K was found to preferentially adsorb on the MgAl2O4 support. A low but still significant K adsorption on S–Ni sites, or an effect on only the fraction of exposed Ni surface area near the metal–support interface, can, however, not be excluded. The result suggests that an improved Ni/MgAl2O4 catalyst activity and an essentially carbon-free operation can be achieved in the presence of controlled amount of gas-phase potassium and high sulfur coverages on Ni. Based on the results, a mechanism of the possible K–S interactions is proposed.

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“…Various catalysts, such as nickel-based catalysts [ 27 ], noble-metal-based catalysts [ 28 ], transition metal catalysts [ 29 ], alkali metal catalysts [ 30 ], natural catalysts [ 31 ], zeolite catalysts [ 32 ], and carbon-supported catalysts [ 33 ] have been investigated for syngas production and tar decomposition from biomass. In general, Ni-based catalysts are considered to be better for catalytic cracking/reforming of tar.…”

Section: Introductionmentioning

confidence: 99%

Insight into the Ex Situ Catalytic Pyrolysis of Biomass over Char Supported Metals Catalyst: Syngas Production and Tar Decomposition

Cui

Xiao

et al. 2020

Nanomaterials

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Ex situ catalytic pyrolysis of biomass using char-supported nanoparticles metals (Fe and Ni) catalyst for syngas production and tar decomposition was investigated. The characterizations of fresh Fe-Ni/char catalysts were determined by TGA, SEM–EDS, Brunauer–Emmett–Teller (BET), and XPS. The results indicated that nanoparticles metal substances (Fe and Ni) successfully impregnated into the char support and increased the thermal stability of Fe-Ni/char. Fe-Ni/char catalyst exhibited relatively superior catalytic performance, where the syngas yield and the molar ratio of H2/CO were 0.91 Nm3/kg biomass and 1.64, respectively. Moreover, the lowest tar yield (43.21 g/kg biomass) and the highest tar catalytic conversion efficiency (84.97 wt.%) were also obtained under the condition of Ni/char. Ultimate analysis and GC–MS were employed to analyze the characterization of tar, and the results indicated that the percentage of aromatic hydrocarbons appreciably increased with the significantly decrease in oxygenated compounds and nitrogenous compounds, especially in Fe-Ni/char catalyst, when compared with no catalyst pyrolysis. After catalytic pyrolysis, XPS was employed to investigate the surface valence states of the characteristic elements in the catalysts. The results indicated that the metallic oxides (MexOy) were reduced to metallic Me0 as active sites for tar catalytic pyrolysis. The main reactions pathway involved during ex situ catalytic pyrolysis of biomass based on char-supported catalyst was proposed. These findings indicate that char has the potential to be used as an efficient and low-cost catalyst toward biomass pyrolysis for syngas production and tar decomposition.

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Equilibrium potassium coverage and its effect on a Ni tar reforming catalyst in alkali- and sulfur-laden biomass gasification gases

Cited by 40 publications

References 55 publications

Naphthalene on Ni(111): Experimental and Theoretical Insights into Adsorption, Dehydrogenation, and Carbon Passivation

Naphthalene on Ni(111): Experimental and Theoretical Insights into Adsorption, Dehydrogenation, and Carbon Passivation

Gas-Phase Potassium Effects and the Role of the Support on the Tar Reforming of Biomass-Derived Producer Gas Over Sulfur-Equilibrated Ni/MgAl₂O₄

Insight into the Ex Situ Catalytic Pyrolysis of Biomass over Char Supported Metals Catalyst: Syngas Production and Tar Decomposition

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Equilibrium potassium coverage and its effect on a Ni tar reforming catalyst in alkali- and sulfur-laden biomass gasification gases

Cited by 40 publications

References 55 publications

Naphthalene on Ni(111): Experimental and Theoretical Insights into Adsorption, Dehydrogenation, and Carbon Passivation

Naphthalene on Ni(111): Experimental and Theoretical Insights into Adsorption, Dehydrogenation, and Carbon Passivation

Gas-Phase Potassium Effects and the Role of the Support on the Tar Reforming of Biomass-Derived Producer Gas Over Sulfur-Equilibrated Ni/MgAl2O4

Insight into the Ex Situ Catalytic Pyrolysis of Biomass over Char Supported Metals Catalyst: Syngas Production and Tar Decomposition

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Product

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Gas-Phase Potassium Effects and the Role of the Support on the Tar Reforming of Biomass-Derived Producer Gas Over Sulfur-Equilibrated Ni/MgAl₂O₄