Structure sensitivity of hydrocarbon synthesis from carbon monoxide and hydrogen

Boudart, M.; McDonald, Mark A.

doi:10.1021/j150655a004

Cited by 121 publications

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“…Results of the catalytic test of sample 2IMDP (Table 2) indicated that the addition of extra amounts of promoters did not affect product selectivity, although it gave rise to an enhanced catalytic activity. This result might suggest that small iron carbide particles have a large number of sites for CH 4 formation that might be difficult to affect with sodium/sulfur. Promoted and unpromoted catalysts prepared by impregnation were tested under FTO conditions at medium pressure (20 bar) to assess the effect of iron carbide particle size on catalytic performance at industrially relevant conditions.…”

Section: Journal Of the American Chemical Societymentioning

confidence: 99%

“…1−3 A catalyst for the selective production of C 2 − C 4 olefins from synthesis gas that has been previously reported consists of iron nanoparticles dispersed on an inert support material. 1,2 The Fischer−Tropsch reaction is recognized as a structuresensitive reaction 4,5 which means that the catalytic performance is strongly related to the particle size of the metal or active phase. The effect of metal particle size has been extensively studied for cobalt 6−10 and ruthenium.…”

Section: ■ Introductionmentioning

confidence: 99%

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Iron Particle Size Effects for Direct Production of Lower Olefins from Synthesis Gas

et al. 2012

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ABSTRACT:The Fischer−Tropsch synthesis of lower olefins (FTO) is an alternative process for the production of key chemical building blocks from non-petroleum-based sources such as natural gas, coal, or biomass. The influence of the iron carbide particle size of promoted and unpromoted carbon nanofiber supported catalysts on the conversion of synthesis gas has been investigated at 340−350°C, H 2 /CO = 1, and pressures of 1 and 20 bar. The surface-specific activity (apparent TOF) based on the initial activity of unpromoted catalysts at 1 bar increased 6−8-fold when the average iron carbide size decreased from 7 to 2 nm, while methane and lower olefins selectivity were not affected. The same decrease in particle size for catalysts promoted by Na plus S resulted at 20 bar in a 2-fold increase of the apparent TOF based on initial activity which was mainly caused by a higher yield of methane for the smallest particles. Presumably, methane formation takes place at highly active low coordination sites residing at corners and edges, which are more abundant on small iron carbide particles. Lower olefins are produced at promoted (stepped) terrace sites that are available and active, quite independent of size. These results demonstrate that the iron carbide particle size plays a crucial role in the design of active and selective FTO catalysts.

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Section: Journal Of the American Chemical Societymentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

Iron Particle Size Effects for Direct Production of Lower Olefins from Synthesis Gas

et al. 2012

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“…Pt NPs (1.5, 2.9, and 5.0 nm) were synthesized with polyvinylpyrolidone (PVP) by existing procedures 1,2 with a TEM image in Figure 1b (Table S1). However, reliable dispersion measurements could not be obtained by this method for dendrimer encapsulated Pt NPs so ethylene hydrogenation, a structure insensitive reaction [12][13][14][15] , was performed to demonstrate an available catalytic surface (Table S1). Although the TOFs of smaller Pt NPs were comparable to results acquired over model Pt surfaces, these values were lower than those of the larger Pt NPs.…”

mentioning

confidence: 99%

Structure Sensitivity of Carbon−Nitrogen Ring Opening: Impact of Platinum Particle Size from below 1 to 5 nm upon Pyrrole Hydrogenation Product Selectivity over Monodisperse Platinum Nanoparticles Loaded onto Mesoporous Silica

et al. 2008

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The ability to control fundamental properties (e.g., particle size, surface structure, and metal-oxide interface) in order to design highly selective heterogeneous catalysts would greatly reduce energy intensive separations. Particle size dependence (i.e., structure sensitivity) upon selectivity can now be examined with well defined nanoparticles (NPs) because of advances in synthetic chemistry. Colloidal chemistry has provided means for synthesizing monodisperse Pt NPs as small as ~2 nm. 1,2 Using a dendrimer templated approach, Pt NPs smaller than 1 nm -a new size regime for studying size induced effects in heterogeneous catalysis -can be synthesized (Scheme 1). 3,4 In this contribution, we report that ring opening for pyrrole hydrogenation is distinctly different for Pt NPs smaller than 2 nm. This insight has not been demonstrated for hydrogenation of cyclic heteroatom bonds to the best of our knowledge. This finding adds fundamental insight into hydrodenitrogenation (HDN) chemistry, which is important for fuel processing and involves removal of N-containing organics. Advances in HDN catalysis are needed to meet new fuel quality regulations because N-containing organics inhibit hydrodesulfurization (HDS) through competitive adsorption 5 and poison acid catalysts 6 , which are used for downstream processing and as supports for HDS catalysts. Pyrrole was selected as the reactant because organics with 5-member N-containing rings are the most common components in fuel. 7,8 Scheme 1. Strategy for Pt NP size control.Pt NPs between 0.8 and 5.0 nm were synthesized by two techniques. For ultrasmall NPs, fourth generation hydroxyl terminated polyamidoamine (PAMAM) dendrimers were used as the templating and capping agent. 4 Synthesis and characterization of Pt 20 and Pt 40 NPs (subscripts denote the average number of metal atoms per NP) have been described. 4,9 The average number of metal atoms per NP is controlled by the Pt ion to dendrimer ratio. Due to difficulties in obtaining accurate size distributions from TEM, sizes were calculated from the average number of metal ions added per dendrimer, which was proven as accurate by X-ray absorption studies. 10 Sizes of Pt 20 and Pt 40 NPs were calculated to be 0.8 and 1.0 nm, respectively. 11 A TEM image ( Figure 1a) of the Pt 60 NPs showed that the Pt size was 1.95 ± 0.27 nm. This size is larger than that expected from the Pt ion to dendrimer ratio and is caused by formation of interdendrimer complexes because the number of Pt atoms per dendrimer approached the number (62) of available internal tertiary amine groups. Pt NPs (1.5, 2.9, and 5.0 nm) were synthesized with polyvinylpyrolidone (PVP) by existing procedures 1,2 with a TEM image in Figure 1b Pt NPs were loaded onto SBA-15 silica (TEM image in Figure 1c for 1.5 nm Pt NPs). For PVP capped NPs, H 2 chemisorption indicated that Pt dispersion decreased as the NP size increased (Table S1). However, reliable dispersion measurements could not be obtained by this method for dendrimer encapsulated Pt NPs so ethylene hydr...

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“…4). When H 2 /CO ratio reaches the theoretical value for methanation, the CH 4 selectivity is about 84 %, while there is still some CO 2 generated, which may be due to competitive reaction between the Boudart reaction and methanation [23,31].…”

Section: Resultsmentioning

confidence: 93%

“…This is a well-known process for Fischer-Tropsch synthesis [23][24][25][26]. For SNG production, -CH 2 -is expected to further hydrogenated into CH 4 rather than link to form the liquid.…”

Section: Resultsmentioning

confidence: 99%

Highly active and selective catalyst for synthetic natural gas (SNG) production

Huang¹,

Chen²,

et al. 2014

Appl Petrochem Res

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A novel nickel-based methanation catalyst has been prepared and tested for CO and CO 2 hydrogenation to synthetic natural gas under various conditions. The catalysts before and after reaction have been characterized using XRD, Laser Raman and IR spectroscopes. It is showed that the novel catalyst can give high methane selectivity and yield at a very broad ranges of temperature and H 2 /CO ratios, although the selectivity to methane increase with the H 2 /CO ratio, which, however, increases with the temperature rising from 200 to 350°C, then gradually decrease. The characterization results showed that the there is surface carbons forming over the catalyst surface, and the nickel crystalline structure changes during the reaction. Despite this, the catalyst still gives the same performance, which suggested that the catalyst can operate in a very broad range conditions.

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Structure sensitivity of hydrocarbon synthesis from carbon monoxide and hydrogen

Cited by 121 publications

References 0 publications

Iron Particle Size Effects for Direct Production of Lower Olefins from Synthesis Gas

Iron Particle Size Effects for Direct Production of Lower Olefins from Synthesis Gas

Structure Sensitivity of Carbon−Nitrogen Ring Opening: Impact of Platinum Particle Size from below 1 to 5 nm upon Pyrrole Hydrogenation Product Selectivity over Monodisperse Platinum Nanoparticles Loaded onto Mesoporous Silica

Highly active and selective catalyst for synthetic natural gas (SNG) production

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