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The goal of this work is to explore the ability of the metal-promoted 25%Co/Al 2 O 3 catalyst to maintain good contact between the metal and cobalt and continue facilitating Co oxide reduction after simulated regeneration cycles through oxidation–reduction treatments, an approach designed to simulate the catalyst regeneration process. Unpromoted 25%Co/Al 2 O 3 catalyst was also subjected to treatments and served as a reference. Seven metal promoters were examined in this work, including Pt, Ru, Re, Ag, Au, Rh, and Ir. Fresh and treated catalysts were evaluated by both TPR and XANES spectroscopy, the latter approach utilizing linear combination fittings with appropriate reference compounds. With the unpromoted catalyst, oxidation–reduction cycles tended to have two effects: (1) a fraction of CoO species that lost their interaction with the support emerged and (2) a fraction of more strongly interacting CoO species was formed. A comparison between the freshly calcined sample and samples subjected to simulated regeneration cycles was demonstrated. Pt-, Ru-, Re-, Ag-, and Rh-promoted 25%Co/Al 2 O 3 catalysts maintained their ability to facilitate Co oxide reduction after undergoing oxidation–reduction cycles even up to 3 cycles, while with Ir- and, especially, Au-25%Co/Al 2 O 3 some losses were observed, suggesting some separation between the promoter and cobalt occurred following the treatment cycles. TPR profiles also suggest that some separation of Ru from Co occurs with simulated regeneration cycles, although it does not impact the extent of reduction of Co after three cycles.

The kinetics of Fischer–Tropsch synthesis (FTS) over a 25%Co/Al2O3 catalyst was studied using a 1-L continuously stirred tank reactor (CSTR) under the conditions of 205–230 °C, 1.4–2.5 MPa, H2/CO = 1.0–2.5 and 3–16 NL/g-cat/h (XCO = 7–54%). Thirty-one sets of kinetic data collected at 220 °C with a low extent of deactivation were used for kinetic parameter regression. The CAER empirical kinetic model ( r F T = k P CO a P H 2 b / ( 1 + m P H 2 O / P H 2 ) ) was employed to study the kinetic effect of water. A positive kinetic water effect was first evidenced using the kinetic approach, consistent with the results of the effect of co-fed water on cobalt FTS in this work and the literature (e.g. Loegdberg et al., 2011 [21] ) for Co/Al2O3 catalysts. The current kinetic results are based on kinetic data taken following an initial catalyst induction period, where the CO conversion had stabilized. These data are different from our earlier investigations where reversible oxidation of small cobalt crystallites and/or catalyst support effects likely impacted the cobalt site densities, resulting in a negative water effect. Thus, in this study, we decoupled the effect of reversible oxidation from the kinetics, so that the effect of water on stable (i.e., presumably larger) metallic cobalt particles could be assessed. In this study, an additional eleven classical FT kinetic models for Co catalysts were tested using the kinetic data. Five of them were also found to adequately describe the kinetic data, including two mechanistic models developed based on carbide mechanisms. The CAER model containing a water effect term and the mechanistic model of Botes et al. (2009) [31] yielded comparable reaction orders for the partial pressures of H2 and CO, resulted in a better fit of the kinetic data.

The effect of halides and potassium addition on cobalt Fischer–Tropsch synthesis (FTS) was studied using 1L CSTR at 493 K, 1.99 MPa and H2/CO of 2.0. The potential catalyst poison was co-fed with syngas after reaching steady-state FTS. Halides were added in an aqueous solution of HX (HF, HCl, HBr) and potassium as aqueous potassium nitrate solution along with syngas at various concentration levels ranging from 500 ppbv to 100 ppmv. Fluoride addition did not affect FT performance of cobalt up to 1.0 ppmv level. However, the presence of other halides (Cl− and Br−) decreased the FT activity proportionally. Addition of potassium decreased cobalt FT activity considerably and increases syngas conversion to methane and CO2 at higher potassium concentrations. The observed poisoning effects for metallic cobalt could be attributed to a blocking effect of cobalt metal sites by halides and potassium in agreement with results of H2 chemisorption on used cobalt FT catalysts.

The performance of carbon-supported cobalt catalysts was compared with that of Co/γ-Al2O3 reference catalysts for the Fischer–Tropsch synthesis (FTS) reaction. The carbon support (CS) was prepared using a hydrothermal method that formed mostly spherical ∼300–800 nm carbons that were first carbonized at 900 °C and then partially graphitized at 1900 °C. The FTS study was conducted using a continuously stirred tank reactor, and the cobalt catalysts were promoted with Pt (0.2% Pt–10% Co) to facilitate the reduction of cobalt oxides. Catalysts were prepared by an evaporative method (Co/CS-IWI) and by a chemical vapor deposition technique (Co/CS-CVD). The CVD technique led to a higher CO conversion (26.5%) relative to the conventional evaporative (IWI) method (7.4%) at the same temperature (220 °C) and space velocity (1.5 NL/gcath). Remarkably, the Co/CS-CVD displayed a high oxygenate selectivity (∼10%) in comparison with cobalt alumina catalysts (i.e., including one having similar Pt and Co loadings, as well a...

The effect of reaction temperature on the performance of a traditional Fischer–Tropsch cobalt catalyst (0.5 % Pt–25 % Co/Al2O3) was investigated during aqueous-phase Fischer–Tropsch synthesis (AFTS) using a 1 L stirred tank reactor in the batch mode of operation. The CO conversion rate of the catalyst was found to increase monotonically with increasing reaction temperature. At lower temperatures oxygenate selectivity was high. With increasing the reaction temperature, oxygenate selectivity decreased and the selectivity to hydrocarbons increased. Carbon dioxide and methane selectivity also increased with reaction temperature and the corresponding higher hydrocarbon (C5+) selectivity decreased. For comparison, the CO conversion rate of the catalyst was also tested using C30 oil as a solvent, and similar activation and reaction conditions were utilized in the batch mode of operation. Slightly higher CO rate was observed with C30 oil as a solvent than with the water.

The effects of pore size (10.8 and 25 nm) and zirconium loading (0–5%) on Fischer–Tropsch synthesis (FTS) performance of 25%Co/Al2O3 catalysts were systematically studied at a CO conversion level of ∼50% under industrially relevant conditions. The catalysts were characterized by adsorption and X-ray spectroscopic techniques in order to understand the relationships between the catalyst physicochemical properties and the FTS performance parameters. Unpromoted wide pore 25%Co/Al2O3 displayed greater stability (CO% rate loss over 150 h of testing: 5.2 versus 27.6%) and 40% higher activity than the narrow pore catalyst. Addition of 1–5% Zr improved the initial activity of the 25%Co/Al2O3 catalysts by 25–71% regardless of support pore size, but the catalyst deactivation rates increased. The activity improvements by Zr for the wide pore and narrow pore catalysts are due to different reasons. XRD, hydrogen-chemisorption, and XANES results suggested that Zr primarily increased Co dispersion for the wide pore catalyst whereas it mainly increased Co reduction for the narrow pore catalysts. The smaller mean Co cluster size observed with the wide pore Co catalyst resulted from a relatively higher fraction of Co residing inside the pores as compared to the narrow pore catalyst. The unpromoted wide pore catalyst exhibited lower CH4 selectivity (5.9–6.3 versus 8.3–8.9%) and higher C5+ selectivity (88–89.2 versus 80–82%) compared with the narrow pore one. Zr addition decreased CH4 selectivity and increased C5+ selectivity for the narrow pore 25%Co/Al2O3 catalyst, but the opposite trend was observed with the wide pore Co catalyst. Explanations for the selectivity trends (including olefins and CO2) are provided based on the effects of Co size and location, and the resulting changes in H2/CO mass transport within pores of the Co/Al2O3 catalysts with and without Zr promoter.

The effect of simulated road aging on the NOx reduction performance of coupled Pt/Rh LNT and Cu-CHA SCR catalysts was studied using H2, CO and C3H6 as NOx reductants. Activity tests showed that the NOx reduction activity of the LNT was significantly decreased after aging, especially at low temperature. N2 physisorption, H2 chemisorption, elemental analysis and TEM results revealed two main changes which account for the degradation in LNT performance. First, residual sulfur in the aged LNT associated with the Ba phase was responsible for decreased NOx storage efficiency. Second, sintering of the precious metals in the washcoat occurred, resulting in decreased contact between the Pt and Ba, and hence in less efficient NOx storage and catalyst regeneration. The aged LNT showed higher NH3 selectivity than that of the fresh LNT in the temperature range 150–450 °C, NH3 generated from the LNT being stored by the SCR catalyst which subsequently catalyzed its reaction with NOx slip from the LNT. Hence, the loss of NOx conversion over the LNT was partly compensated by the downstream SCR catalyst. N2O formation over the aged LNT was less than that over the fresh LNT and the N2O was partly mitigated by the downstream SCR catalyst. Microreactor tests further showed that in addition to NH3, the SCR catalyst was able to use slipped CO or C3H6 as NOx reductants. A comparison of the difference in NOx conversion for the aged LNT and LNT–SCR configurations for the three reductants used in this study showed that the greatest benefit was obtained when CO and C3H6 were the reductants. This is explained by the fact that the LNT catalyst was unable to utilize these reductants as efficiently as H2 due to their lower reactivity; hence, more NOx and reductant slip reached the SCR catalyst. The ability of the SCR catalyst to utilize these reductants therefore provides a significant advantage over the LNT-only configuration.

The effects of process conditions on Fischer–Tropsch synthesis (FTS) product distribution were studied using a 1-L stirred tank slurry reactor and a 0.48%Re–25%Co/Al 2 O 3 catalyst. It was found that the chain growth probability of C 1 intermediate ( α 1 ) has the most dominant effect on CH 4 and C 5+ selectivity. α 1 was found to be highly dependent on process conditions. Relatively constant values of C 2+ growth probabilities with reactor residence time, as well as other process variables, suggest that 1-olefin readsorption has a minor effect on product selectivities. A low value of α 1 and its different response to variations in process conditions, compared to higher chain growth probabilities, seems to support a hypothesis that a higher-than-expected yield of methane is caused by at least two separate methane formation pathways. Understanding these pathways and ways to suppress excess methane formation is a key factor in obtaining higher C 5+ selectivity.

This focused review article underscores how metal reduction promoters can impact deactivation phenomena associated with cobalt Fischer-Tropsch synthesis catalysts. Promoters can exacerbate sintering if the additional cobalt metal clusters, formed as a result of the promoting effect, are in close proximity at the nanoscale to other cobalt particles on the surface. Recent efforts have shown that when promoters are used to facilitate the reduction of small crystallites with the aim of increasing surface Co0 site densities (e.g., in research catalysts), ultra-small crystallites (e.g.

The kinetics and the effect of indigenous and externally added water on methane formation during Fischer–Tropsch synthesis (FTS) was studied over Co based catalysts using a 1 L continuously stirred tank reactor (CSTR). The water cofeeding study (10% water) was conducted over a 0.27%Ru–25%Co/Al2O3 catalyst at a low CO conversion level of 19% at 220 °C in order to lessen the effect of catalyst aging during the addition of water, while the kinetic experiment was conducted over 25%Co/γ-Al2O3 at the conditions of 205–230 °C, 1.4–2.5 MPa, H2/CO = 1.0–2.5, and 3–16 (NL/gcat)/h (XCO < 60%). Indigenous and externally added water decreases methane formation by a kinetic effect. The addition of 10% water led to a decrease in the CH4 rate by 12% (3.5 → 3.0 (mmol/gcat)/h), while little catalyst deactivation was observed during water addition. Increases in indigenous water partial pressure also lowered the CH4 rate and its selectivity. Kinetic analysis was performed using a group of 220 °C data collected between 365 an...

The effects of 1% of Cd, In and Sn additives on the physicochemical properties and Fischer-Tropsch synthesis (FTS) performance of a 15% Co/Al2O3 catalyst were investigated. The fresh and spent catalysts were characterized by BET, temperature programmed reduction (TPR), H2-chemisorption, NH3 temperature programmed desorption (TPD), X-ray absorption near edge spectroscopy (XANES), and X ray diffraction (XRD). The catalysts were tested in a 1 L continuously stirred tank reactor (CSTR) at 220 &deg, C, 2.2 MPa, H2/CO = 2.1 and 20&ndash, 55% CO conversion. Addition of 1% of Cd or In enhanced the reduction degree of 15%Co/Al2O3 by ~20%, while addition of 1% Sn slightly hindered it. All three additives adversely impacted Co dispersion by 22&ndash, 32% by increasing apparent Co cluster size based on the H2-chemisorption measurements. However, the decreased Co active site density resulting from the additives did not result in a corresponding activity loss, instead, the additives decreased the activity of the Co catalysts to a much greater extent than expected, i.e., 82&ndash, 93%. The additional detrimental effect on catalyst activity likely indicates that the Cd, In and Sn additives migrated to and covered active sites during reaction and/or provided an electronic effect. XANES results showed that oxides of the additives were present during the reaction, but that a fraction of metal was also likely present based on the TPR and reaction testing results. This is in contrast to typical promoters that become metallic at or below ~350 &deg, C, such as noble metal promoters (e.g., Pt, Ru) and Group 11 promoters (e.g., Ag, Au) on Co catalysts in earlier studies. In the current work, all three additives remarkably increased CH4 and CO2 selectivities and decreased C5+ selectivity, with the Sn and In additives having a greater effect. Interestingly, the Cd, In, or Sn additives were found to influence hydrogenation and isomerization activities. At a similar conversion level (i.e., in the range of 40&ndash, 50%), the additives significantly increased 2-C4 olefin content from 3.8 to 10.6% and n-C4 paraffin from 50 to 61% accompanied by decreases in 1-C4 olefin content from 48 to 30%. The Sn contributed the greatest impact on the secondary reactions of 1-olefins, followed by the In and Cd. NH3-TPD results suggest enhanced acid sites on cobalt catalysts resulting from the additives, which likely explains the change in selectivities for the different catalysts.

Accumulation of products is a known phenomenon associated with a continuously stirred tank reactor (CSTR). Secondary reactions of α-olefins due to prolonged bed/pore residence time can significantly change the primary Fischer–Tropsch product distribution. Using D2 as a tracer, this study first investigated the significance of Fischer–Tropsch product accumulation in a CSTR. Secondly, the D2 tracer study was used to investigate primary product distribution and olefin to paraffin ratios. Based on the D2 study, it was found that Fischer–Tropsch synthesis with a 2.5 % Ru/NaY catalyst follows a single α mechanism with a chain growth probability of about 0.74. Both olefins and paraffins are primary products and the ruthenium catalyst produced a similar olefin/paraffin ratio for each carbon number. The apparent decline of the O/P ratio for higher carbon number products was shown to be due to secondary reactions of the olefin at prolonged residence times. D2 tracing was shown to be a versatile tool to investigate product accumulation and to define primary product distribution which is very important for mechanistic interpretation and kinetic modeling.

The active sites for Fischer–Tropsch synthesis are surface cobalt metal atoms. In order to obtain a high dispersion for reaction, ultra-small cobalt clusters (e.g., 1 nm) were supported on KL-zeolite using a chemical vapor deposition procedure. A Pt promoter was added to facilitate reduction of the cobalt oxide species. Upon activation in hydrogen, a high dispersion was obtained, but after exposure to realistic FT conditions in a pressurized continuously stirred tank reactor reactor, XANES and EXAFS results indicate that the fine cobalt clusters were susceptible to reoxidation, resulting in adverse activity and selectivity (30–37 % CH4 and 3.5–4.0 % CO2 on a C% basis).

The effect of K loading on the water–gas shift (WGS) reaction and hydrocarbon formation rate during Fischer–Tropsch synthesis (FTS) was studied over 100 Fe/5.1 Si/2 Cu/x K (x = 1.25 or 3) precipitated catalysts using a 1-L continuously stirred tank reactor. The catalysts were tested over a wide range of experimental conditions: 260–270 °C, 1.3 MPa, H2/CO = 0.67 and 20–90 % CO conversions. On the low K loading (1.25 % K) Fe catalyst, the H2 deficiency required for the FTS reaction was made up by the WGS reaction only at high CO conversion level, i.e. >70 %; however, increasing potassium loading to 3 % dramatically improved the WGS reaction rate which provided enough hydrogen for the FTS reaction even at low CO conversion level, i.e. 30 %. Kinetic analysis suggests that increasing K loading resulted in significant increases in the WGS rate constant relative to that of FTS, which is a major cause of the high WGS activity on the high K loading catalyst. Both the low and high potassium containing iron catalysts have high liquid oil and solid wax formation rates, i.e. 0.78–0.93 g/g-cat/h at 260 °C, 1.3 MPa, H2/CO = 0.67 and 50 % CO conversion, but increasing potassium loading from 1.25 to 3 % shifted the primary product to wax (70 %) from oil (73.5 %). The wax fraction increased with increasing CO conversion for both iron catalysts. The effect of K loading on initial FTS activity and hydrocarbon distribution/selectivity of the Fe catalysts was also studied. High K loading, i.e. 3 % K, increased the iron carburization rate and significantly shortened the induction period of the FTS reaction. Secondary reactions of olefins were remarkably suppressed and the olefin content was greatly enhanced with increasing K loading from 1.25 to 3 %, consistent with a number of studies in the open literature.

The performance of catalysts derived from LaCo1−xCuxO3 (x = 0.0 or 0.2) perovskite-type oxides for steam reforming (SR) and oxidative SR of ethanol at 773 K was evaluated. All catalysts deactivated during SR of ethanol. In the absence of Cu, the increase of calcination temperature from 873 to 1,073 K did not affect the stability of the samples. On the other hand, for the samples containing Cu, it was detected a higher rate of deactivation when the calcination temperature was increased. The loss of activity of LaCoO3 was attributed to the oxidation of Co metallic particles and amorphous carbon formation as revealed by in situ XAFS and thermogravimetric analyses. The addition of Cu favored the formation of carbon filaments. Moreover, the presence of oxygen in the feed decreased the carbon formation, improving the stability of the catalysts.

The isotopic effect of D2 was investigated for a 2.5 % Ru/NaY catalyst for Fischer–Tropsch synthesis at industrially relevant conditions (493 K, 1.92 MPa, H2/CO = 2). An inverse kinetic isotopic effect was found for CO conversion (rD/rH = 1–1.4) and methane formation (1.2–1.4), suggesting that H is involved in the rate determining steps of both reactions. D2 enhanced methane formation and inhibited C2+ formation and therefore decreased chain growth probability. The decline in rD/rH with carbon number is due to increasing dependence on the ratio (

The effect of co-fed ammonia in syngas on the performance of a traditional cobalt catalyst (platinum promoted cobalt/alumina) was investigated during Fischer–Tropsch synthesis (FTS) using a continuously stirred tank reactor (CSTR). The addition of 1, 10, 100, and 1200 ppmw (concentration of ammonia with respect to the syngas feed) of ammonia resulted in significant irreversible deactivation of the catalyst under identical reaction conditions. The percentage of deactivation was almost constant (±5%) at all the concentrations (1–1200 ppmw) of ammonia exposure. The addition of ammonia (either NH 3 gas or aqueous NH 4 OH) particularly at higher concentrations exhibits lower methane selectivity compared to ammonia-free synthesis conditions. This enhancement in C 5 + hydrocarbon formation may be attributed to the selective poisoning of metallic cobalt sites by addition of ammonia.

The sensitivity of 100Fe/5.1Si/2Cu/3K Fischer–Tropsch synthesis (FTS) catalyst to the impurities of KCl, NaCl, KHCO3 and NaHCO3 in syngas (0.1–100 ppm) was studied in a slurry phase reactor at 533.2 or 543.2 K, H2/CO = 0.67–0.77, 1.31 MPa and 10 NL/g-cat/h. The impurities were co-fed with syngas, and the influence of each contaminant concentration on Fe catalyst behavior was examined for 72–144 h. The presence of up to 40 ppmw halide compounds (NaCl and KCl) or alkali bicarbonates (NaHCO3 and KHCO3) in syngas at 543.2 K or up to 100 ppm of NaCl and KCl at 533.2 K had little impact on the Fe catalyst activity and selectivities to CH4, C5+ and C4 olefin and 1-olefin during 400 h (543.2 K) or 1400 h testing (533.2 K). CO2 selectivity slightly increased after feeding the impurity-containing solutions, which was due to enhanced water gas shift (WGS). ICP results for the Fe catalysts at the end of the FTS reaction test and of the FTS products (i.e., water, oil or wax phase) indicate that the impurity ions (K+, Na+ or Cl−) introduced were present in all phases of the FTS products, the greater part being retained in the wax. Therefore, the contaminant ions (i.e., Na, K or Cl) in the water solution injected appear to not strongly adsorb on the Fe catalyst surface at typical FTS conditions in the slurry phase reactor. This is assumed to be responsible for the lack of change in FTS behavior for the Fe catalyst using the contaminants studied.

Sulfur in the form of H2S has been added at various concentration levels during cobalt Fischer–Tropsch synthesis. A steady-state FTS conversion was established prior to adding H2S. At low levels (

By using different catalyst pretreatments, silica supported cobalt catalysts were activated to produce either hcp or fcc cobalt metal particles, as verified by XRD. H2-TPR and pulse re-oxidation experiments show a higher dispersion of cobalt for the catalyst containing the hcp metallic phase compared to the fcc phase. Cobalt containing hcp metallic phase has shown higher CO conversion on a catalyst weight basis and less methane selectivity compared to fcc containing catalysts under similar reaction conditions. Both hcp and fcc phases of cobalt are stable during the Fischer–Tropsch (FT) synthesis.

This article reviews the use of synchrotron radiation techniques to confront issues associated with cobalt and iron catalysts. The main areas that are examined include: (1) the application of TPR-XANES and TPR-EXAFS to gain insight into the hydrogen reduction of cobalt catalysts and the carburization of iron catalysts; (2) the impact of promoters on these reduction/carburization rates; (3) the local atomic structure of promoters and its influence on catalyst selectivity; (4) exploring the deactivation of cobalt catalysts; (5) the influence of crystallite size in stabilizing cobalts catalyst against water effects; and (6) temperature effects in alkali promoted iron catalysts in retaining the iron carbide phase against reoxidation by water.

The effect of CO conversion on methane selectivity of a 10 % Co/TiO2 catalyst was investigated using a 1L continuously stirred tank reactor at 493–503 K, 2.4 MPa, H2/CO = 2 and GHSV = 0.4–6 Nl g cat −1 h−1. The cobalt catalysts were activated by H2 and CO, respectively, in two separate runs. For the H2 activated catalyst, the methane selectivity decreased (15–6 %) and C5+ selectivity increased (80–91 %) linearly with increasing CO conversion from 10 to 60 %. The C2–C4 hydrocarbon selectivity decreased slightly with CO conversion. The enhancement in C5+ selectivity was mainly due to the decrease in methane selectivity. The CO activated cobalt catalyst was initially in a carburized form after activation, and then converted to a form with greater metallic character when exposed to syngas at Fischer–Tropsch conditions. The CO activated catalyst at pseudo steady-state had higher methane selectivity in general as compared to the H2 activated one, possibly due to the presence of the cobalt carbide phase. Two kinetic regions appear to exist for the CO activated catalyst. When CO conversion is lower than 20 %, the methane selectivity increased exponentially with CO conversion, which is attributed to enhanced hydrogenation. When CO conversion is higher than 20 %, the CO activated catalyst behaves more like a H2 activated catalyst, with a decrease in methane and an increase in C5+ selectivity with CO conversion.

Heterogeneous nickel catalysts play an important role in numerous processes. In the past, a number of H/D isotopic labeling studies have probed catalytic mechanisms during specific associative and dissociative steps. The current work investigates the adsorption of hydrogen on Ni0 sites, the active surface where H-transfer reactions take place, to determine if preferential partitioning of H or D occurs on the metal surface. This is important for understanding whether differences in surface coverages between H and D could potentially impact KIE analyses. Overall, when H2 and D2 were added competitively to either H-activated NiO or Ni/alumina catalysts, no significant isotopic preference was identified. However, when the catalyst was pretreated with H2 (or D2) prior to flowing the equimolar mixture, a slight isotopic preference for H2 (or D2) was observed. This residual effect suggests that, in both cases, hydrogen exchange with hydroxyl groups on the support occurred. That is, in the case of hydrogen activated NiO, the resulting catalyst is likely a mixture of Ni and residual NiO, the latter presumably containing surface hydroxyl groups. The isotopic preference when H2 (or D2) pretreatment is conducted prior to running the H2/D2 (50–50 %) mixture is enhanced when alumina is used as a support due to greater OH/OD exchange. A similar, but even less pronounced effect, was observed previously with cobalt/alumina catalysts.

For economic reasons, Ag as a substitute for Pt promoter for FT Co/Al2O3 catalysts was advocated, due to its satisfactory ability to facilitate cobalt oxide reduction, its good catalytic performance in improving the CO conversion and selectivity and, especially, its much lower price compared to that of Pt (i.e., $23.31/Troy oz Ag. vs $1486.0/Troy oz Pt (May 10, 2013)). A comparative study between Pt and Ag promoters at several equivalent atomic loadings was performed in this work. While either Pt or Ag significantly facilitates cobalt oxide reduction supplying additional Co metal active sites compared to the unpromoted Co/Al2O3 catalysts, the total metal site density increased with increasing Pt loading, but become attenuated at high Ag loading. The EXAFS results indicate isolated Pt atoms interact with cobalt clusters to form Pt–Co bonds, without evidence of Pt–Pt bond formation, even at levels as high as 5 wt% Pt. In Ag promoted Co/Al2O3 catalyst, not only were Ag–Co bonds observed, but Ag–Ag bonds were present, even at levels as low as 0.276% Ag. The degree of Ag–Ag coordination increased as a function of Ag loading, while decreases in BET surface area and a shift to wider average pore size suggests some pore blocking by Ag at high loadings, which likely restricted access of reactants to internal cobalt sites. Therefore, although both promoters initially facilitate reduction of cobalt oxides, their local atomic structures are fundamentally different. Either Pt or Ag can significantly improve the CO conversion rate on a per gram catalyst basis of Co/Al2O3. Slightly adverse effects on selectivity (i.e., increased CH4 and CO2, at detriment to C5+) were found with Pt, especially at higher loading, while Ag provides some benefits (i.e., slightly decreases CH4 and CO2, and increases C5+) at all loadings tested in this work. Moreover, TPR and chemisorption/pulse reoxidation results show that Pt and Ag continue to be in proximity with Co following oxidation–reduction (OR) cycles to continue to facilitate reduction. Additional reaction tests are required to determine the impact of regeneration on performance.

CO2 hydrogenation was investigated with a doubly promoted (Cu, K) silica containing iron catalyst. Hagg carbide (χ-Fe5C2) is the dominant phase obtained under CO activation conditions at 543 K and 0.1 MPa and it was stable under FTS conditions typical for coal or biomass derived syngas using a H2/CO ratio of 1:1 for at least ∼100 h TOS. An Fe-phase change occurs (χ-Fe5C2 → Fe3O4) after switching from H2:CO:N2 (1:1:2) to H2:CO2 (3:1). The distribution of hydrocarbon products changes significantly after switching to H2:CO2 (3:1), but then it slowly transformed to normal FTS products, albeit with over 3 times higher methane selectivity compared to FTS using H2:CO:N2 (1:1:2). A correlation was obtained between the rate of FTS and the % of Fe carbide indicating that iron carbide is the active phase for CO2-based FT synthesis. Irrespective of conditions (i.e., either H2:CO:N2 = 1:1:2 or H2:CO2 = 3:1) and the Fe phase, the methane selectivity appears to primarily depend on the H2/CO ratio.

The effect of start-up solvent on the performance of cobalt-based catalysts and potassium-promoted precipitated iron catalysts was investigated during Fischer–Tropsch (FT) synthesis by using a continuously stirred tank reactor. In this study, four different molecular weight start-up solvents were tested: Polywax-3000 ( $$\overline{MW}$$ (average molecular weight) = 3,000), Polywax-2000 ( $$\overline{MW}$$ = 2,000), Polywax-500 ( $$\overline{MW}$$ = 500) and C-30 oil ( $$\overline{MW}$$ = 420). The conversion and selectivities (methane, C5+ and CO2) were essentially the same for all the start-up solvents tested for the potassium promoted precipitated iron catalysts suggesting that there was no significant effect of startup solvent for the iron catalyst tested. However, with the cobalt catalyst, conversion varied with solvent, with the conversion increasing with decreasing molecular weight of the solvent. This is considered to be due to the particle size of the cobalt alumina catalysts being large relative to that of iron that was used. Under synthesis conditions, the iron catalyst attrits to form a measurable fraction of 1–3 micron sized particles in the lower range of the particle size distribution, whereas the alumina support retains essentially the same, larger size during synthesis. Thus, the decrease in conversion with time is likely to be a result of pore filling with solvent into the interior of the catalyst, which increases with increasing molecular weight of the start-up solvent. In obtaining conversion and aging data for FT catalysts, wax accumulation needs to be considered.

The influence of zeolite structure for the alkylation of biphenyl with propylene was studied over various zeolites such as HY, HZSM-5, and dealuminated mordenite (DMOR), as well as amorphous SiO2/Al2O3, in a stirred tank reactor. Biphenyl conversion was found to increase with reaction time for HZSM-5 and DMOR zeolites and reach a leveling off in 4 h, whereas for HY and amorphous SiO2/Al2O3 a leveling off was reached within an hour. DMOR displayed the highest selectivity for 4,4′-diisopropylbiphenyl (4,4′-DIPB) even at temperatures as high as 300 °C, whereas for HY, HZSM-5 and amorphous SiO2/Al2O3 selectivities fell in the range of 10–35%; they were significantly lower than observed for DMOR. These differences in selectivity might be due to the structure and pore channels of the zeolites. DMOR was found to be an active catalyst, the selectivity for 4-isopropylbiphenyl (4-IPB) and (4,4′-DIPB) was high among isopropylbiphenyl (IPB) and diisopropylbiphenyl (DIPB) isomers, respectively, indicating DMOR possesses shape-selectivity. The selectivity of 4,4′-DIPB increased with time, while the corresponding selectivity of 4-IPB decreased for DMOR catalyst. Alkylation of biphenyl with propylene occurred with predominant formation of 4-IPB in the first step. 4-IPB is only a source in the second step of alkylation of biphenyl with propylene for the formation of 4,4′-DIPB, while 3-IPB does not participate in the formation of DIPB isomers.

The hydroisomerization and hydrocracking of long chain n-paraffins and a Fischer–Tropsch wax produced with a cobalt catalyst were accomplished over a Pt–amorphous silica–alumina catalyst. The relative conversion of the n-hexadecane and n-octacosane mixed feed greatly favored the higher carbon number compound even though the conversions of the pure hydrocarbons were the same within a factor of two or less when converted separately. Thus, vapor equilibrium plays a role for the conversion of the heavier alkanes and in this case the conversion essentially occurs with only the compound present in the liquid phase. The single branched cracked products show a peak at the mid-carbon number, C8 and C14 for the two reactants, but the peak for the multi-branched product occurs at a higher carbon number. Thus, it appears that the multi-branched products are primarily produced in a series reaction with the singly branched compounds being formed as the primary products. The data for wax conversion are consistent with the competitive conversion operating for the higher carbon number compounds; however, the transport of intermediate carbon number products from the reactor occurs more rapidly than their formation rates by cracking reactions. The data clearly show that the hydrocracking of wax is dominated by vapor–liquid equilibrium and that hydrocracking is initially controlled by the compounds present in the liquid phase. Figure shows the catalyst pore filling with low boiling (left) and high boiling (right) hydrocarbons. Each reactant saturates the catalytic sites and the breaking of C–C bond occurs. Once the products from cracking of the liquid phase go into the vapor phase, it should rapidly pass the catalyst bed. This short contact time on gas phase hydrocarbons relative to the liquid phase, limits the conversion of low boiling point hydrocarbons.

The effect of CO conversion (35–91 %) on hydrocarbon product distribution (CH4, C5 + and olefin selectivities) and CO2 selectivity was studied in a fixed bed reactor on 15 % Co/Al2O3 catalyst at conditions of industrial relevance. Selectivity to CH4 decreased, whereas those of C5 + and CO2 increased with increasing CO conversion (and consequently, partial pressure of water produced during the Fischer–Tropsch synthesis). 1-Olefin content of C2–C5 olefins decreased and 2-olefin content of C4 hydrocarbon increased with increasing CO conversion.

Pt-promoted tungsten-hafnia catalysts containing different amounts of tungsten (15 and 20 wt% WO3) were prepared and tested for hydroisomerization of n-hexadecane in a trickle-bed reactor. All catalysts were calcined under dry air flow at 723 K for 3 h. Pt-promoted sulfated hafnia was also prepared for the purpose of comparison. The catalysts were characterized using BET surface area, X-ray diffraction, and DRIFTS for the adsorption of pyridine. Tungsten-based hafnia catalysts exhibit moderate activity ( 95 %), which had an operating temperature of 493 K. However, tungsten-based hafnia catalysts were more selective towards iso-C16 even at higher n-hexadecane conversions. More cracking products were obtained with sulfated hafnia in which the selectivity to iso-C16 decreases exponentially with n-hexadecane conversion. The less acidic tungsten–hafnia catalysts may be suitable for producing more isomerized products compared to the sulfated analog.

The effect of deuterium on Fischer-Tropsch (FT) synthesis was investigated over a Pt promoted Co/CeO2 catalyst. CeO2 supported Pt–Co catalyst is more selective towards methane and oxygenates. H2–D2–H2 switching experiments suggest that the hydrogenation of CO is involved in the rate determining step (inverse isotope effect). The suppression of oxygenate formation with deuterium leads to the conclusion that common FT intermediates are responsible for the observed shift in the product spectrum. The deuterium isotopic study supports our previously proposed mechanism for the formation of alcohols in that the Co–CeO2 interface is involved in the catalysis, such that termination of chain growth occurs at the metal–oxide junction and involves bridging OH groups on partially reduced ceria.

To define the mechanism of the Fischer–Tropsch synthesis, numerous experiments probed the rate-determining step by performing isotopic experiments during CO hydrogenation. The aim of this work was to determine if there is an isotopic effect for adsorption for either hydrogen or deuterium on the cobalt metal surface of a Fischer–Tropsch synthesis catalyst. If a partitioning effect is noticed, there is a possibility for this to interfere with measurements of the inverse kinetic isotopic effect during CO hydrogenation. In this investigation, the partitioning of hydrogen and deuterium on an activated cobalt catalyst was examined using temperature programmed desorption and gas chromatography. The results indicate that there may be hydrogen–deuterium exchange with the support, but there is no significant isotopic partitioning on the cobalt metal surface.

The catalytic gas phase hydrogenation of 1,3-dinitrobenzene over Au/Al2O3 delivered exclusive reduction of a single −NO2 substituent to generate 1,3-nitroaniline (Ea = 131 kJ mol–1), reaction over Ni/Al2O3 resulted in full hydrogenation to 1,3-phenylenediamine (Ea = 38 kJ mol–1), whereas both products were isolated over Au–Ni/Al2O3. In the hydrogenation of 1,3,5-trinitrobenzene, Au/Al2O3 promoted preferential partial hydrogenation (3,5-dinitroaniline), Ni/Al2O3 generated 1,3,5-triaminobenzene as the predominant product, while Au–Ni/Al2O3 exhibited an intermediate catalytic response. The catalysts have been characterized in terms of temperature programmed reduction (TPR), H2 chemisorption, powder XRD, high-resolution TEM, XPS, and XANES/EXAFS measurements. Post-TPR, there was evidence of a metal particle redispersion resulting from the introduction of Au to Ni/Al2O3 where HRTEM-EDX mapping has established close proximity of Au and Ni on Au–Ni/Al2O3 with electron transfer from Ni to Au (from XPS analysis). ...