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In this contribution, we examine the effect of the promoter´s ionic charge and valence orbital energy on the catalytic activity of Fe-based catalysts, based on in situ synchrotron X-ray powder diffraction (SXRPD), temperature-programmed-based techniques (TPR, TPD, CO-TP carburization), and Fischer–Tropsch synthesis catalytic testing studies. We compared the promoting effects of K (a known promoter for longer-chained products) with Ba, which has a similar ionic radius but has double the ionic charge. Despite being partially “buried” in a crystalline BaCO3 phase, the carburization of the Ba-promoted catalyst was more effective than that of K, this was primarily due to its higher (2+) ionic charge. With Ba2+, higher selectivity to methane and lighter products were obtained compared to the K-promoted catalysts, this is likely due to Ba´s lesser capability of suppressing H adsorption on the catalyst surface. An explanation is provided in terms of a more limited mixing between electron-filled Ba2+ 5p and partially filled Fe 3d orbitals, which are expected to be important for the chemical promotion, as they are further apart in energy compared to the K+ 3p and Fe 3d orbitals.

Different low-cost cobalt precursors (acetate, chloride) and thermal treatments (air calcination/H2 reduction versus direct H2-activation) were investigated to alter the interaction between cobalt and silica. H2-activated catalysts prepared from cobalt chloride had large Co0 particles (XRD, chemisorption) formed by weak interactions between cobalt chloride and silica (temperature programmed reduction (TPR), TPR with mass spectrometry (TPR-MS), TPR with extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge spectroscopy (XANES) techniques) and retained Cl-blocked active sites, resulting in poor activity. In contrast, unpromoted Co/SiO2 catalysts derived from cobalt acetate had strong interactions between Co species and silica (TPR/TPR-MS, TPR-EXAFS/XANES), adding Pt increased the extent of the Co reduction. For these Pt-promoted catalysts, the reduction of uncalcined catalysts was faster, resulting in larger Co0 clusters (19.5 nm) in comparison with the air-calcined/H2-activated catalyst (7.8 nm). Both catalysts had CO conversions 25% higher than that of the Pt-promoted catalyst prepared in the traditional manner (air calcination/H2 reduction using cobalt nitrate) and three times higher than that of the traditional unpromoted Co/silica catalyst. The retention of residual cobalt carbide (observed in XANES) from cobalt acetate decomposition impacted performance, resulting in a higher C1–C4 selectivity (32.2% for air-calcined and 38.7% for uncalcined) than that of traditional catalysts (17.5–18.6%). The residual carbide also lowered the α-value and olefin/paraffin ratio. Future work will focus on improving selectivity through oxidation–reduction cycles.

Direct reduction of cobalt nitrate versus conventional calcination/reduction treatment was conducted using alumina with identical methodology as previously applied to SiO2 and TiO2. Similar BET surface areas, pore volumes and pore size distributions were obtained for the activated calcined and uncalcined catalysts indicating no significant difference in morphological properties. However, the reducibility slightly increases and Co crystallite size is smaller for activated uncalcined samples. Reduction phenomena were analyzed by TPR-MS and TPR-EXAFS/XANES. Combining these techniques allows an explanation of the complex phenomena occurring during the direct reduction of cobalt nitrate, as both nitrate decomposition and cobalt oxide reduction are involved. Cobalt nitrate species are converted to CoOx intermediates. These species are oxidized by NOX (from nitrate decomposition) to Co3O4 spinel, which is converted to CoO prior to Co0 formation. Noble metals (Pt, Re, Ru and Ag) improve cobalt oxide reducibility, especially for the final reduction step (i.e., CoO to Co0). The effect of direct nitrate reduction on FT activity was investigated using a 1 L CSTR. Activated unpromoted and Pt-promoted uncalcined catalysts achieved higher initial and steady-state CO conversions in comparison to the corresponding calcined catalysts. The best performance was achieved with direct reduction of uncalcined 0.5 %Pt-25 %Co/Al2O3.

This work studied the performance of nickel phosphide phases supported on various supports (SiO2, Al2O3, TiO2, CeO2 and CeZrO2) for the hydrodeoxygenation of phenol in gas phase at 300 °C and 1 atm. The nature of the phosphide phase obtained by the temperature programmed reduction at 700 °C depended on the type of support. Only Ni2P was formed on SiO2, TiO2, and CeZrO2, whereas the Ni12P5 was the preferred phase on Al2O3. A mixture of both Ni2P and Ni12P5 phases was obtained on CeO2. Unsupported Ni2P exhibited high selectivity to benzene (95%), indicating that the Ni2P phase is responsible for the direct deoxygenation of phenol. Ni12P5 phase promoted the formation of cyclohexanone, cyclohexane and cyclohexene. However, the supported catalysts showed lower selectivity to benzene, even when the Ni2P was the only phase present. The supports favored the formation of hydrogenation products via the tautomerization route. All catalysts only slightly deactivated with time on stream, which is likely due to the high activity of the phosphide phase.

Quantitative data comparing iron and cobalt based catalysts for the Fischer-Tropsch synthesis (FTS) are scarce due to the fact that these two kinds of catalysts typically utilize different process conditions. This paper focuses on studying the catalytic behavior of two highly active iron and cobalt based research catalysts at clean conditions and during poisoning with common syngas contaminants. The catalyst activity and selectivity at identical conditions, the CO conversion effect, and the effect of poisons on iron and cobalt catalysts were systematically explored in a quantitative manner. At a set of identical FTS conditions, the cobalt catalyst was 2.5 times as active as the iron catalyst with higher CH4 and C5+ selectivities but much less olefins and lower CO2 selectivity. Cobalt based catalysts are more susceptible to deactivation by oxidation at high CO conversions (e.g. > 80%) due to the high partial pressure of water (PH2O) in the reactor, while the iron catalyst can be stabilized at a high conversion level. Under clean FTS conditions, the cobalt catalysts displayed a more pronounced CO conversion effect on stability and selectivity; on the other hand, a combination of effects (i.e. from CO conversion and the nature of the catalyst) were observed for the iron catalysts. The sensitivities of the Fe and Co catalysts to the typical contaminants (i.e., H2S and NH3) present in the syngas derived from coal, natural gas or biomass were compared. Iron and cobalt catalysts exhibited similar resistance to the H2S poison (i.e. threshold levels 25–50 ppb), but the iron catalyst was found to be much more resistant to ammonia than the cobalt catalyst (i.e., threshold levels of 80 ppm and 45 ppb, respectively). Co-feeding 150–200 ppm ammonia lowered CH4 selectivity and 2-olefin content (suppressing secondary reactions of 1-olefin) on both types of catalysts. In contrast, co-feeding up to 1 ppm H2S significantly increased CH4 formation only on cobalt catalysts but had a minor effect on CH4 selectivity with iron catalysts. It increased 2-olefin content (enhanced secondary reactions of 1-olefin) regardless of catalyst type. H2S and NH3 have different impacts on H2, CO adsorption, and the formation of sulfur and nitride compounds have been proposed to explain these dissimilar effects.

The effect of the nature of the lanthanide (Ln = La, Ce, Pr, Sm, Gd) on the structure and reactivity of Co/SiO2 catalysts for CO hydrogenation (i.e., Fischer Trospch synthesis) was investigated. In-situ temperature programmed reduction with extended x-ray absorption fine structure and x-ray absorption near edge spectroscopy (TPR-EXAFS/XANES) of the structure of both Co and Ln containing phases under activation and CO hydrogenation conditions were performed. Concerning catalyst selectivity (made at comparable conversion levels), while methane selectivity was higher for the Gd-doped catalyst (∼100%, relative) compared to the unpromoted catalyst, the selectivity to olefins plus alcohols and C2-C4 products was higher (∼35%, relative), compared to the unpromoted catalyst. The Ce-promoted Co/SiO2 catalyst presented the highest oxygenate/olefin selectivity (∼40%), among the promoted catalysts tested at a similar conversion level of ∼20%. Under reactive conditions (both following H2 activation and during CO+H2 flow), a mixture containing small LnOX/CoO/Co° nanocrystallites likely constitute the active sites during reaction. These results imply that the presence of the lanthanide likely introduces surface defects in the oxides (LnOX and/or CoO) located at the metallic cobalt nanoparticle rim which may serve as active sites for active O-containing species (e.g., mobile Type II OH groups) that may either serve as chain termination species, or generate chain terminating species such as formates (i.e., essentially molecularly adsorbed CO) upon CO adsorption.

The decomposition selectivity of formaldehyde during steam reforming was explored using unpromoted and sodium promoted Pt/m-ZrO2 catalysts, and the Na content was varied (0.5%Na, 1%Na, 1.8%Na, 2.5%Na, and 5%Na). In situ DRIFTS experiments during temperature programmed reaction in flowing H2O revealed that formaldehyde is adsorbed at reduced defect sites on zirconia, where it is converted to formate species through the addition of labile bridging OH species. Formate species achieve a maximum intensity in the range of 125–175 °C, where only slight changes in intensity are observed. Above this temperature, the formate decomposition reactivity strongly depends on the Na loading, with the optimum loadings being 1.8%Na and 2.5%Na. CO2 temperature programmed desorption results, as well as a greater splitting observed between the formate νasym(OCO) and νsym(OCO) bands in infrared spectroscopy, indicate greater basicity is induced by the presence of Na. This strengthens the interaction between the formate -CO2 functional group and the catalyst surface, weakening the formate C-H bond. A shift in the ν(CH) band of formate to lower wavenumbers was observed by addition of Na, especially at 1.8%Na and higher loadings. This results in enhanced decarboxylation and dehydrogenation of formate, as observed in in situ DRIFTS, temperature-programmed reaction/mass spectrometry experiments of the steam reforming of formaldehyde, and fixed bed reaction tests. For example, 2.5%Na addition of 2.5% increased the CO2 selectivity from 83.5% to 99.5% and the catalysts achieved higher stable conversion at lower temperature than NiO catalysts reported in the open literature. At 5%Na loading, Pt sites were severely blocked, hindering H-transfer.

The decarboxylation pathway in ethanol steam reforming ultimately favors higher selectivity to hydrogen over the decarbonylation mechanism. The addition of an optimized amount of Cs to Pt/m-ZrO2 catalysts increases the basicity and promotes the decarboxylation route, converting ethanol to mainly H2, CO2, and CH4 at low temperature with virtually no decarbonylation being detected. This offers the potential to feed the product stream into a conventional methane steam reformer for the production of hydrogen with higher selectivity. DRIFTS and the temperature-programmed reaction of ethanol steam reforming, as well as fixed bed catalyst testing, revealed that the addition of just 2.9% Cs was able to stave off decarbonylation almost completely by attenuating the metallic function. This occurs with a decrease in ethanol conversion of just 16% relative to the undoped catalyst. In comparison with our previous work with Na, this amount is—on an equivalent atomic basis—just 28% of the amount of Na that is required to achieve the same effect. Thus, Cs is a much more efficient promoter than Na in facilitating decarboxylation.

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.

This work studies the effect of support defect sites on the performance of Pd/CexZr1-xO2 (x = 0.00; 0.25; 0.50; 0.75; 0.90) catalysts for the hydrodeoxygenation of phenol in the gas phase at 573 K. The activity and selectivity for hydrodeoxygenation of phenol depends significantly on the support used. Increasing the Zr content from x = 0.0 to 0.5, the reaction rate for hydrodeoxygenation and the selectivity to benzene remains very low. However, upon increasing the Zr content above x = 0.5 a sudden jump in reaction rate and selectivity to benzene is observed. Interestingly, this activity and selectivity boost has no direct correlation with the density of acid sites or the concentration of defects on the support. Rather, the selectivity to deoxygenated products is found to depend on the oxophilicity of the support. Increasing the Zr content enhances the strength of the interaction between the O of the carbonyl group and the oxophilic site. It is proposed that the oxophilicity of these catalysts is related to the structure of the CexZr1-xO2 solid solution formed. In addition, it is observed that the degree of deactivation during the reaction also depends on the Ce/Zr molar ratio of the support. Pd/ZrO2, Pd/Ce0.10Zr0.90O2 and Pd/Ce0.25Zr0.75O2 catalysts readily deactivate during reaction, whereas the phenol conversion only slightly decreases for Pd/CeO2, Pd/Ce0.75Zr0.25O2 and Pd/Ce0.50Zr0.50O2 catalysts. The results reveal that the density of Zr species on the surface is responsible for catalyst deactivation. The stronger adsorption between the oxygen from the phenol with Zr cations resulted in an accumulation of O-containing byproducts and catalyst deactivation.

The effect of the direct reduction of cobalt nitrate versus the more conventional calcination/reduction treatment has been investigated. Porosity properties of the catalysts are not significantly modified by avoiding the calcination step, as similar BET surface area, pore volume and pore diameter are obtained for the activated catalysts. In contrast, the cobalt reducibility decreases, but smaller cobalt particles size and higher dispersion are obtained. The reduction phenomena occurring for the uncalcined catalysts are more complex because of the additional nitrate decomposition steps. TPR-MS and TPR-XANES point out that CoOx intermediate species are formed during the reductive nitrate decomposition. However, these species are oxidized by NOX (formed by nitrate decomposition) to spinel type Co3O4, which is then converted to CoO prior to the final reduction step to Co0. The addition of promoters (Pt, Re, Ru, Ag) improves the cobalt reducibility, especially by shifting the final reduction step (i.e., CoO to Co0) to lower temperature. FT activity testing data show that activated uncalcined catalysts have higher CO conversion following the initial decline and leveling off period relative to the activated calcined catalyst. The best performance is achieved with uncalcined Pt-12%Co/TiO2. This catalyst has the highest CO steady state conversion, which is 1.2 times higher than the Pt-promoted calcined catalyst. Moreover, its deactivation rate is 0.13%/h compared to 0.2%/h for the corresponding calcined catalyst. The difference in the catalytic activity is even higher for the un-promoted samples, where the activated uncalcined catalyst has almost double the CO conversion as compared to its calcined counterpart. Finally, the addition of other promoters such as Ru, Re and Ag has no significant effect on catalytic activity.

The effect of alkali promoter (K, Rb and Cs) on the performance of precipitated iron-based catalysts was investigated for carbon dioxide (CO2) hydrogenation. Characterization by temperature-programmed reduction with CO, Mossbauer spectroscopy, and transmission electron microscopy were used to study the effect of alkali promoter interactions on the carburization and phase transformation behavior of the catalysts. Under similar reaction conditions, cesium (Cs) and rubidium (Rb) promoted catalysts exhibited the highest initial CO2 conversions to higher hydrocarbons. CO2 conversions then decreased to reach steady state conversions around 170 h on stream. At steady state conversion, all three catalysts exhibited similar CO2 conversions and selectivities. For comparison, a lower loaded Cs (1.5 Cs) promoted iron-based catalyst was prepared. It exhibited slightly lower initial conversion than the higher loaded Cs catalyst, but remained very stable. Among all the catalysts at steady state conversion, the 1.5 Cs promoted catalyst exhibited the highest stability. Results indicate a synergistic effect brought on by these promoters that, if balanced, could potentially yield superior CO2 hydrogenation catalysts.

Recent studies have shown that appropriate levels of alkali promotion can significantly improve the rate of low-temperature water gas shift (LT-WGS) on a range of catalysts. At sufficient loadings, the alkali metal can weaken the formate C–H bond and promote formate dehydrogenation, which is the proposed rate determining step in the formate associative mechanism. In a continuation of these studies, the effect of Rb promotion on Pt/ZrO2 is examined herein. Pt/ZrO2 catalysts were prepared with several different Rb loadings and characterized using temperature programmed reduction mass spectrometry (TPR-MS), temperature programmed desorption (TPD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), an x-ray absorption near edge spectroscopy (XANES) difference procedure, extended x-ray absorption fine structure spectroscopy (EXAFS) fitting, TPR-EXAFS/XANES, and reactor testing. At loadings of 2.79% Rb or higher, a significant shift was seen in the formate ν(CH) band. The results showed that a Rb loading of 4.65%, significantly improves the rate of formate decomposition in the presence of steam via weakening the formate C–H bond. However, excessive rubidium loading led to the increase in stability of a second intermediate, carbonate and inhibited hydrogen transfer reactions on Pt through surface blocking and accelerated agglomeration during catalyst activation. Optimal catalytic performance was achieved with loadings in the range of 0.55–0.93% Rb, where the catalyst maintained high activity and exhibited higher stability in comparison with the unpromoted catalyst.

Developing routes of utilizing CO2 emissions is important for long-term environmental preservation, as storing such emissions underground will eventually become unsustainable. One way of utilizing CO2 emissions is as a light-oxidant feedstock for oxidative dehydrogenation of propane (ODHP) to propylene. However, the adsorption and reaction steps typically occur at widely different temperatures, meaning that the thermal gradients – and by extension process energy requirements – are often unreasonably high. In recent years, dual-functional materials (DFMs) – i.e., materials comprised of a high temperature adsorbent phase alongside a heterogeneous catalyst – have been employed for combined CO2 adsorption and utilization over one material within a single bed using a reduced thermal gradient. However, these materials have never been formed into practical contactors and have never been applied to ODHP applications. Therefore, in this study we manufactured the first-generation of DFM adsorbent/catalyst monoliths, comprised of CaO (adsorbent) and M@ZSM-5 (M = V-, Ga-, Ti-, or Ni-oxide) heterogeneous catalysts, using our novel direct metal-oxide 3D printing technique. The monoliths were vigorously characterized using N2 physisorption, C3H8-DRIFTS, NH3-TPD, Py-FTIR, H2-TPR, XRD, XPS, and elemental mapping and were assessed for CO2 capture/ODHP utilization at 600–700 oC. The adsorption/catalysis experiments revealed that these materials can perform both processes effectively at 600 oC, with reduced propylene yield at higher temperature, which eliminated the need for a thermal gradient between the adsorption and catalysis steps. Between the various samples, the Ti-doped monolith generated the best balance of CO2 conversion (76%) and propylene selectivity (39%), due to the high dispersion of TiO2, favorable redox properties and controlled acidity of the dopant. However, it was also found that varying the metal dopant could be used to control the heuristics of CO2/C3H8 conversion, C3H6 selectivity, and C3H6 yield, meaning that the manufacturing process outlined herein represents a promising way of tuning the chemical properties of structured DFM adsorbent/catalyst materials. More importantly, this study establishes a promising proof-of-concept for 3D printing as a facile means of structuring these exciting composite materials and expands DFMs to the previously unexplored application of ODHP.

In this work, the effect of interfacial sites between Pd particles and Nb2O5 species is investigated by testing a series of Pd-Nb2O5/SiO2 catalysts with different niobium loadings for the HDO reaction of phenol in the gas phase. Important differences in the selectivity to deoxygenated product were observed depending on the presence of niobium oxide close to Pd particles, which reveals the key role of the type of active phase in the control of reaction steps. It was found that Pd/SiO2 catalyst promotes hydrogenation pathways, producing cyclohex-anone as the major product. For Pd-Nb2O5/SiO2 catalyst containing a Nb/Pd molar ratio of 0.5, a sharp increase in the selectivity to benzene is observed (7.5-fold). Increasing the Nb/Pd molar ratio, the formation of benzene is enhanced. The results showed that the Pd-Nb2O5 interface, composed by an oxophilic oxide in the perimeter of the metal particle, is responsible for the activation of the C-O bond, promoting the deoxygenation reaction.

The effect of cobalt substitution with nickel was investigated for the Fischer&ndash, Tropsch synthesis reaction. Catalysts having different Ni/Co ratios were prepared by aqueous incipient wetness co-impregnation, characterized, and tested using a continuously stirred tank reactor (CSTR) for more than 200 h. The addition of nickel did not significantly modify the morphological properties measured. XRD, STEM, and TPR-XANES results showed intimate contact between nickel and cobalt, strongly suggesting the formation of a Co-Ni solid oxide solution in each case. Moreover, TPR-XANES indicated that nickel addition improves the cobalt reducibility. This may be due to H2 dissociation and spillover, but is more likely the results of a chemical effect of intimate contact between Co and Ni resulting in Co-Ni alloying after activation. FTS testing revealed a lower initial activity when nickel was added. However, CO conversion continuously increased with time on-stream until a steady-state value (34%&ndash, 37% depending on Ni/Co ratio) was achieved, which was very close to the value observed for undoped Co/Al2O3. This trend suggests nickel can stabilize cobalt nanoparticles even at a lower weight percentage of Co. Currently, the cobalt price is 2.13 times the price of nickel. Thus, comparing the activity/price, the catalyst with a Ni/Co ratio of 25/75 has better performance than the unpromoted catalyst. Finally, nickel-promoted catalysts exhibited slightly higher initial selectivity for light hydrocarbons, but this difference typically diminished with time on-stream, once leveling off in conversion was achieved, the C5+ selectivities were similar (&asymp, 80%) for Ni/Co ratios up to 10/90, and only slightly lower (&asymp, 77%) at Ni/Co of 25/75.

This work investigated the effect of the addition of a second metal (Cu, Ag, Zn, Sn) on the performance of Pd/ZrO2 catalyst for HDO of phenol at 573 K in the gas phase. The incorporation of dopants resulted in the formation of Pd–X (Cu, Ag, Zn) alloys, which reduced the reaction rate for HDO and increased the selectivity to hydrogenation products (cyclohexanone and cyclohexanol). For PdSn/ZrO2, alloying was also observed but tin oxide was still present on the surface after reduction at 773 K. For Pd/ZrO2 and PdSn/ZrO2, the oxophilic sites represented by Zr and Sn cations promotes the hydrogenation of the carbonyl group of the keto-tautomer intermediate formed, producing benzene as the main product. All catalysts significantly deactivated during the reaction but the deactivation degree depended on the type of the metal. Pd/ZrO2 and PdZn/ZrO2 and PdAg/ZrO2 exhibited approximately the same deactivation degree. However, the loss of activity was less pronounced for PdSn/ZrO2 catalyst. Pd dispersion significantly decreased during the reaction, indicating that the sintering of Pd particles is one of the causes for catalyst deactivation.

The explanation for CH4 selectivity for iron based Fischer-Tropsch catalysts in the low conversion region (i.e.

This work investigates the performance of Pd supported on SiO 2 and Nb 2 O 5 for the HDO of phenol reaction at different temperatures using a fixed-bed reactor. The type of support significantly affects activity and product distribution. The reaction rate for HDO of phenol over Pd/Nb 2 O 5 was 90-fold higher than that observed for silica supported catalyst. Cyclohexanone was the dominant product for Pd/SiO 2 , whereas benzene was mainly formed on Pd/Nb 2 O 5 . The high activity and selectivity to deoxygenated products of Pd/Nb 2 O 5 for HDO of phenol is likely due to the strong interaction between the oxophilic sites represented by Nb 5+ /Nb 4+ cations and the oxygen from the phenol molecule. This promotes hydrogenation of the carbonyl function, resulting in the formation of 2,4-cyclohexadienol, which is dehydrated to benzene. For Pd/SiO 2 catalyst, the hydrogenation of the ring is the main reaction pathway observed. The reaction pathway was also affected by the reaction temperature, the hydrogenation of the carbonyl group being favored at high temperature.

As a follow-up to a previous alkali chloride poisoning study, the effect of up to 100 ppm KCl on the Fischer-Tropsch synthesis (FTS) performance of representative iron (Fe-Si-Cu doped with Rb as the alkali) and cobalt (Pt-Co/Al 2 O 3 ) catalysts was studied at 270 °C and 230 °C, respectively, by co-feeding KCl in a water/ethylene glycol (EG) solution. The used catalysts were characterized by XANES at the K and Cl K-edges; furthermore, ICP was used to analyze residual K and Cl ions possibly remaining in the FTS products. KCl was found to be a weak poison for the iron and cobalt catalysts. The addition of 20–100 ppm KCl deactivated the catalysts to only a low to moderate extent. For the cobalt catalyst, less than 25 ppm KCl was found to give negligible deactivation. The added KCl and EG-H 2 O solvent was found to slightly modify the selectivity for both catalysts, such that KCl slightly promoted light hydrocarbon formation as well as olefins and slightly suppressed C 5+ and 2-olefin formation, while the EG-H 2 O solvent was found to have a different effect on the C 1 C 4 and C 5+ selectivities. It appears that K and Cl played opposite roles in modifying hydrocarbon selectivities. The ICP results suggested 48–98% K and Cl ions were adsorbed by the iron catalyst. XANES results confirmed the presence of K and Cl ions on the used iron and cobalt catalysts and showed a structure with characteristics that were similar to bulk KCl. Two possible mechanisms, including site blocking by K and Cl ions and electronic modification impacting CO/H 2 adsorption, were proposed to explain the deactivating effect of KCl on the iron and cobalt catalysts.

Zirconia was used to support Ru, Ni, and Ru-Ni bimetallic nanoparticles for CO2 methanation. The formation of an alloy was detected in Ru K-edge spectra. The Ru/ZrO2 exhibited the highest CO2 reaction rate (1.35 mol/molmetal.s) with a CH4 selectivity of 97.3%. The diffuse reflectance infrared fourier transform spectroscopy experiments suggest that formates serve as intermediates in converting CO2 to CO via reverse water–gas shift at the interface between Ru and defect-sites on zirconia, while Ru metal intercepts CO, further hydrogenating it to CH4. The better performance of Ru/ZrO2 could be related to the Ru-zirconia interface and Ru on-top atoms, which promote the reverse water gas shift and the CO hydrogenation reactions. Thus, this work provided important information about the effect of alloying Ru with Ni on the performance of the catalyst for the CO2 methanation, as well as the mechanism of this reaction for the best catalyst, Ru/ZrO2.

Ga- and In-modified ceria (Ce 0.8 Ga 0.2 O 2 , Ce 0.8 In 0.2 O 2 ) materials were used as supports for cobalt-catalyzed Fischer-Tropsch synthesis (FTS). The addition of Ga to ceria was found to improve CO conversion for cobalt-catalyzed FTS, while the addition of In tended to decrease it. A similar trend was observed with the Ag-promoted cobalt/ceria catalysts. Doping of ceria with Ga or In decreased methane and increased the selectivity to olefins and alcohols for Ag-promoted cobalt/ceria. The sum of the products of olefins and alcohols for various catalysts exhibited a decreasing trend as follows: Ag-Co/Ce-Ga > Ag-Co/Ce-In > Ag-Co/Ce. Results of H 2 -TPR-XANES showed that adding of Ga or In to ceria increases the fraction of Ce 3+ in the surface shell for both unpromoted and Ag-promoted catalysts in the range of temperature typical of catalyst activation. This partially reduced ceria plays an important role in controlling the product selectivity of cobalt-catalyzed FT synthesis.

In previous work, Na-doping of Pt/YSZ was found to facilitate the low temperature water gas shift reaction (LT-WGS), and the promoting effect was ascribed to an electronic weakening of the C H bond of the formate species, a proposed intermediate in the catalytic cycle. Formate has also been implicated as an intermediate in steam-assisted formic acid decomposition (SAFAD) and methanol steam reforming (MSR) pathways. In the current contribution, Na-doping was also found to significantly accelerate the SAFAD reaction. The high activity of Pt/YSZ for SAFAD, as well as the promoting effect of Na, are in stark contrast to the view that formates are too stable, precluding them as intermediates for LT-WGS. With MSR, a remarkable promoting effect of Na doping was observed in the selectivity to CO 2 (>90% for Na-doped relative to 22% for undoped at 300 °C); however, at the doping levels used in the current work, the activity was lower for the Na doped catalyst and further optimization is needed to improve MSR conversion.

XANES K-edge spectra of potassium promoter in precipitated Fe catalysts were acquired following activation by carburization in CO and as a function of time on-stream during the course of a Fischer–Tropsch synthesis run for a 100Fe:2K catalyst by withdrawing catalysts, sealed in wax product, for analysis. CO-activated and end-of-run spectra of the catalyst were also obtained for a 100Fe:5K catalyst. Peaks representing electronic transitions and multiple scattering were observed and resembled reference spectra for potassium carbonate or potassium formate. The shift in the multiple scattering peak to higher energy was consistent with sintering of potassium promoter during the course of the reaction test. The catalyst, however, retained its carbidic state, as demonstrated by XANES and EXAFS spectra at the iron K-edge, suggesting that sintering of potassium did not adversely affect the carburization rate, which is important for preventing iron carbides from oxidizing. The method serves a starting point for developing better understanding of the chemical state and changes in structure occurring with alkali promoter.

The effect of the sequence of phosphorous and cobalt addition to silica on the activity and product selectivity for Fischer-Tropsch synthesis was investigated using a slurry phase continuously stirred-tank reactor. Advantages of P-modified silica supported cobalt included higher activity and C5+ selectivity in comparison with both the undoped and P-doped cobalt silica catalysts. Results of hydrogen chemisorption revealed that cobalt dispersion was higher for all three P-containing cobalt catalysts compared to the undoped cobalt catalyst. H2-TPR profiles indicate P increases the fraction of high-temperature reducible cobalt oxide species and these surface species were dominant in the case of co-impregnated and P-doped cobalt silica catalysts. P-modified silica had enhanced FT activity likely by altering the surface interactions of cobalt with the hydroxyl groups on silica.

The effects of co-fed ammonia in synthesis gas on the activity and product selectivities of a typical cobalt catalyst (0.5% Pt–25% Co/Al2O3) were investigated during the Fischer–Tropsch synthesis using a continuously stirred tank reactor (CSTR). The product selectivities were compared at a similar CO conversion level for various concentrations (10–1000 ppmv) of ammonia, as well as clean (un-poisoned) conditions. The addition of 10–1000 ppmv ammonia (concentration of ammonia with respect to the syngas feed) significantly decreased activity; the percentage of deactivation was similar (∼40%) for the various concentrations of ammonia used. At similar CO conversions, the addition of ammonia caused an increase in olefin selectivity and the corresponding paraffin and alcohol selectivities were decreased compared to the ammonia free synthesis conditions. Olefin selectivity increased with increasing concentration of ammonia, and the paraffin and alcohol selectivities were decreased with increasing ammonia concentration. At similar CO conversions, ammonia addition exhibited a positive effect on hydrocarbon selectivity (i.e., lower light gas products and higher C5+) and also light gas product selectivities (C1–C4) were decreased and C5+ selectivity increased with increasing concentration of ammonia compared to ammonia free conditions.

Samples of well-controlled nanoparticles consisting of alloys of cobalt and nickel of different atomic ratios were synthesized using wet chemical methods with oleylamine as the solvent and the reducing agent. These materials were characterized by a variety of techniques, including high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), X-ray energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). Small amounts of heterogenized catalysts were prepared using alumina as the support. However, the potential for use of Co&ndash, Ni catalysts in CO hydrogenation was explored using a larger amount of Co&ndash, Ni/alumina catalyst prepared from standard aqueous impregnation methods and tested in a continuously stirred tank reactor (CSTR) for Fischer&ndash, Tropsch synthesis (FTS). Results are compared to a reference catalyst containing only cobalt. The heterogenized catalysts were characterized using synchrotron methods, including temperature programmed reduction with extended X-ray absorption fine structure spectroscopy and X-ray absorption near edge spectroscopy (TPR-EXAFS/XANES). The characterization results support intimate contact between Co and Ni, strongly suggesting alloy formation. In FTS testing, drawbacks of Ni addition included decreased CO conversion on a per gram catalyst basis, although Ni did not significantly impact the turnover number of cobalt, and produced slightly higher light gas selectivity. Benefits of Ni addition included an inverted induction period relative to undoped Co/Al2O3, where CO conversion increased with time on-stream in the initial period, and the stabilization of cobalt nanoparticles at a lower weight % of Co.

Cobalt and iron have long history of importance in the field of catalysis that continues to this day [...]

Nearly a century ago, Fischer and Tropsch discovered a means of synthesizing organic compounds ranging from C1 to C70 by reacting carbon monoxide and hydrogen on a catalyst. Fischer&ndash, Tropsch synthesis (FTS) is now known as a pseudo-polymerization process taking a mixture of CO as H2 (also known as syngas) to produce a vast array of hydrocarbons, along with various small amounts of oxygenated materials. Despite the decades spent studying this process, it is still considered a black-box reaction with a mechanism that is still under debate. This investigation sought to improve our understanding by taking data from a series of experimental Fischer&ndash, Tropsch synthesis runs to build a computational model. The experimental runs were completed in an isothermal continuous stirred-tank reactor, allowing for comparison across a series of completed catalyst tests. Similar catalytic recipes were chosen so that conditional comparisons of pressure, temperature, SV, and CO/H2 could be made. Further, results from the output of the reactor that included the deviations in product selectivity, especially that of methane and CO2, were considered. Cobalt was chosen for these exams for its industrial relevance and respectfully clean process as it does not intrinsically undergo the water&ndash, gas shift (WGS). The primary focus of this manuscript was to compare runs using cobalt-based catalysts that varied in two oxide catalyst supports. The results were obtained by creating two differential equations, one for H2 and one for CO, in terms of products or groups of products. These were analyzed using sensitivity analysis (SA) to determine the products or groups that impact the model the most. The results revealed a significant difference in sensitivity between the two catalyst&ndash, support combinations. When the model equations for H2 and CO were split, the results indicated that the CO equation was significantly more sensitive to CO2 production than the H2 equation.

The bulk of the products that were synthesized from Fischer&ndash, Tropsch synthesis (FTS) is a wide range (C1&ndash, C70+) of hydrocarbons, primarily straight-chained paraffins. Additional hydrocarbon products, which can also be a majority, are linear olefins, specifically: 1-olefin, trans-2-olefin, and cis-2-olefin. Minor hydrocarbon products can include isomerized hydrocarbons, predominantly methyl-branched paraffin, cyclic hydrocarbons mainly derived from high-temperature FTS and internal olefins. Combined, these products provide 80&ndash, 95% of the total products (excluding CO2) generated from syngas. A vast number of different oxygenated species, such as aldehydes, ketones, acids, and alcohols, are also embedded in this product range. These materials can be used to probe the FTS mechanism or to produce alternative chemicals. The purpose of this article is to compare the product selectivity over several FTS catalysts. Discussions center on typical product selectivity of commonly used catalysts, as well as some uncommon formulations that display selectivity anomalies. Reaction tests were conducted while using an isothermal continuously stirred tank reactor. Carbon mole percentages of CO that are converted to specific materials for Co, Fe, and Ru catalysts vary, but they depend on support type (especially with cobalt and ruthenium) and promoters (especially with iron). All three active metals produced linear alcohols as the major oxygenated product. In addition, only iron produced significant selectivities to acids, aldehydes, and ketones. Iron catalysts consistently produced the most isomerized products of the catalysts that were tested. Not only does product selectivity provide a fingerprint of the catalyst formulation, but it also points to a viable proposed mechanistic route.

Certain alkali metals (Na, K) at targeted loadings have been shown in recent decades to significantly promote the LT-WGS reaction. This occurs at alkali doping levels where a redshift in the C-H band of formate occurs, indicating electronic weakening of the bond. The C-H bond breaking of formate is the proposed rate-limiting step of the formate associative mechanism, lending support to the occurrence of this mechanism in H2-rich environments of the LT-WGS stage of fuel processors. Continuing in this vein of research, 2%Pt/m-ZrO2 was promoted with various levels of Cs in order to explore its influence on the rate of formate intermediate decomposition, as well as that of LT-WGS in a fixed bed reactor. In situ DRIFTS experiments revealed that Cs promoter loadings of 3.87% to 7.22% resulted in significant acceleration of the forward formate decomposition in steam at 130 °C. Of all of the alkali metals tested to date, the redshift in the formate ν(CH) band with the incorporation of Cs was the greatest. XANES difference experiments at the Pt L2 and L3 edges indicated that the electronic effect was not likely due to an enrichment of electronic density on Pt. CO2 TPD experiments revealed that, unlike Na and K promoters, Cs behaves more like Rb in that the decomposition of the second intermediate in LT-WGS, carbonate species, is hindered due to (1) increased basicity of Cs, (2) the tendency of Cs to cover Pt sites that facilitate CO2 decomposition, and (3) the tendency of Cs to increase Pt particle size as shown by EXAFS results, resulting in fewer Pt sites that facilitate CO2 decomposition. As such, the LT-WGS rate was hindered overall and the rate-limiting step shifted to carbonate decomposition (CO2 removal). Like its Rb counterpart, low levels of added Cs (e.g., 0.72%Cs) were found to improve the stability of the catalyst relative to the unpromoted catalyst, the stability comparison was made at similar CO conversion level as well as similar space velocity.

Ethanol steam reforming (ESR) was investigated on unpromoted and several sodium promoted Pt/ZrO2 catalysts. From DRIFTS experiments, the following steps during ESR were inferred: dissociation of ethanol to produce ethoxy species; oxidative dehydrogenation of ethoxy species to acetate; and acetate decomposition. Acetate decomposition depends on the catalyst formulation. Decarboxylation is the most favored route at high sodium loading (2.5 and 5 wt.%); acetate decomposes in the forward direction to CH4 and a carbonate, which further decomposes to CO2. In contrast, decarbonylation is prevalent for the unpromoted catalyst or catalysts having low sodium loading. Acetate likely decomposes to CH3OH and CO. Adsorbed methanol may undergo further steam reforming by oxidative dehydrogenation to formate species, which decarbonylates via reverse decomposition to CO and H2O. Temperature programmed desorption/reaction and activity data confirmed that alkali promotion, especially at 1.8 %Na and higher loading, facilitates the forward acetate decomposition step, favoring decarboxylation over decarbonylation.

A large number of kinetic data points (83 sets) was obtained over a wide range of CO conversion (7–90%), pressure (1.3–2.5 MPa) and H 2 /CO ratio (0.67–1.5) with an iron catalyst (100 Fe/5.1 Si/1.25 K). The kinetics of the catalyst in the low (X CO CO > 70%) regions were studied separately. Twenty six Fischer–Tropsch synthesis (FTS) and water gas shift (WGS) kinetic models were tested and discriminated. Water and CO 2 inhibition was evaluated. While all thirteen FTS models gave a satisfactory fit, the new FTS models that included CO 2 inhibition surpassed the others. Water inhibition of the FTS rate was insignificant over both low and high conversion ranges. For the WGS kinetics of the iron catalyst, a newly constructed empirical model and one from the literature provided the best fits of the WGS rates, while nine mechanistic models and one power law WGS model were unable to satisfactorily fit the WGS kinetic data. Water did not significantly limit the WGS rate and CO 2 only inhibited the rate at high CO conversions. The equations obtained for the low and high CO conversion ranges varied greatly. The errors for the models for 85% of the FTS and WGS data points were less than 10%, and the errors of the remaining points fell in the range of 10–15%.

The effect of phosphorus addition on silica-supported cobalt catalyst was investigated for Fischer-Tropsch synthesis (FTS). As shown by STEM images and chemisorption, the addition of phosphorus to cobalt of up to 1 wt% increased the dispersion of cobalt. Further addition of phosphorus (e.g., 3 and 5 wt.%), as demonstrated by TPR, pulse reoxidation, and XANES, significantly hindered the reduction of cobalt oxides. The cobalt FTS catalysts containing 0.5 and 1.0 wt% P exhibited greater stability in comparison with undoped and 3.0 wt% P containing cobalt catalysts. Analysis of XANES spectra at the P and Co K-edges, along with DRIFTS results of H 2 -activated cobalt catalysts, suggest that cobalt particles interact with PO 4 3− ions, indicating a role played by P in anchoring Co particles to the support, thus hindering the cobalt sintering rate. The initial selectivity to methane was slightly higher for 0.5%P-20%Co/SiO 2 and 1.0%P-20%Co/SiO 2 catalysts compared to the undoped catalyst, but at longer times differences were small. At higher loadings of P (3 wt.%), FT activity and selectivity were adversely and irreversibly affected.

The effect of co-fed hydrogen chloride (HCl) in syngas on the performance of iron and cobalt-based Fischer–Tropsch (FT) catalysts was investigated in our earlier studies (Ma et al. in ACS Catal 5:3124–3136, 2015; Davis et al., DOE final report, 2011; Gnanamani et al. in Catal Lett 144:1127–1133, 2014). For an iron catalyst, lower HCl concentrations (

The effect of solvent on the hydrogen-deuterium isotopic homomolecular exchange rate over a 26.4% Ni/Al2O3 catalyst was investigated using a plug flow reactor at room temperature (23 °C) and at atmospheric pressure. In this study, two different molecular weight solvents were tested: n-pentane ( M W ¯ (average molecular weight) = 72), and n-hexadecane ( M W ¯ = 226). At dry (without addition of solvent) and n-pentane solvent addition conditions, similar amounts of H2 and D2 are consumed and the concentration of the HD produced is two times the consumption of H2 or D2. Thus, these conditions exhibited around 100% exchange with the formation of H2:HD:D2 having a 1:2:1 ratio. With n-hexadecane solvent, the initial exchange rate was approximately 45%, but the exchange rate decreased with time and reached a steady state rate after 60 min on-stream. The lower exchange rate of the n-hexadecane solvent might be due to the limited mobility of reactant molecules in the liquid-filled pores of the catalyst. The exchange rate of the catalyst is decreased with increasing molecular weight and density of the solvent. An isotopic partitioning preference was not observed for the nickel catalyst under various co-fed solvents, and similar findings were observed in our previous work (Catalysis Letters 143 (2013) 1368–1373).

The effect of ammonia in syngas on the performance of various supported cobalt catalysts (i.e., Al2O3, TiO2 and SiO2) was investigated during Fischer–Tropsch synthesis (FTS) using a continuously stirred tank reactor (CSTR). The addition of ammonia (10 ppmv NH3) caused a significant deactivation for all supported cobalt catalysts, but the rate of deactivation was higher for the silica-supported catalysts relative to the alumina and titania-supported catalysts used in this work. Ammonia addition had a positive effect on product selectivity (i.e., lower light gas products and higher C5+) for alumina and titania-supported catalysts compared to ammonia free conditions, whereas, the addition of ammonia increased lighter hydrocarbon (C1–C4) products and decreased higher hydrocarbon (C5+) selectivity compared to ammonia-free synthesis conditions for the silica-supported catalyst. For alumina and titania-supported catalysts, the activity almost recovered with mild in-situ hydrogen treatment of the ammonia exposed catalysts. For the silica-supported catalyst, the loss of activity is somewhat irreversible (i.e., cannot be regained after the mild hydrogen treatment). Addition of ammonia led to a significant loss in BET surface area and changes in pore diameter (consistent with pore collapse of a fraction of pores into the microporous range as described in the literature), as well as formation of catalytically inactive cobalt support compounds for the silica-supported catalyst. On the other hand, the pore characteristics of alumina and titania-supported catalysts were not significantly changed. XANES results of the ammonia exposed silica-supported catalysts further confirm the formation of cobalt-support compounds (cobalt silicates).

Sequential impregnation and calcination were used to fill the pores of a commercial alumina support with alumina. In this manner, two different pore-modified alumina supports were synthesized. To account for the diminished pore size, cobalt loadings were lowered as appropriate to ensure a similar cobalt size range (e.g., clusters 14–18 nm in diameter) and comparable extents of reduction. This was confirmed by measurements from TPR, hydrogen chemisorption/pulse reoxidation, and EXAFS/XANES spectroscopies. Catalysts were tested using a slurry phase CSTR reactor at commercially relevant FTS conditions. Selectivities were compared at both high and low levels of conversion for the catalyst series. Decreasing the pore length, as measured by PSD data, appears to lessen the adverse effect that the higher relative diffusional rate of hydrogen versus carbon monoxide has on the H2/CO surface fugacity ratio on the catalyst surface. That is, moving the cobalt particles closer to the pore mouth may prevent the H2/CO ratio from being augmented at the surface of cobalt particles due to diffusion or other factors, and inhibits excessive chain termination that would lead to higher light product selectivities. Pore filling thus results in a catalyst that is similar to an egg-shell catalyst. With increased pore filling by alumina, C1 C4 light gas selectivities decreased, in a systematic way, by as much as 33% (relative basis), and the C5+ selectivity improved by as much as 10.3% (relative basis) in comparison with the 22.4%Co/Al2O3 (IWI) reference catalyst. This greater effectiveness offers an opportunity for more environmentally benign chemical processing.

The sulfur limit, the relationship between the sulfur added and the surface Fe atoms lost (Fe/S), and mechanism of sulfur poisoning were studied using an iron Fischer–Tropsch synthesis (FTS) catalyst (100 Fe/5.1 Si/2.0Cu/3.0K). The FTS reaction was carried out at 230–270 °C, 1.3 MPa, H2/CO = 0.67–0.77 and 30–70% CO conversion using a 1-L slurry phase reactor. The used Fe catalysts were characterized by XRD, Mossbauer spectroscopy and XANES spectroscopy to understand the deactivation mechanism of the Fe based catalyst after adding up to 1 ppm H2S in the feed. Co-feeding of 0.1 ppm H2S in syngas for 70 h caused a very small change in the activity of the Fe catalyst, but increasing the H2S level to 0.2 ppm or above resulted in measurable deactivation of the Fe catalyst over a similar time period. The limit of sulfur level in the syngas feed (sensitivity) was determined to be 50 ppb. The added sulfur improved the selectivities of the secondary reactions of olefins and the WGS reaction even though the rates for these declined. The addition of H2S decreased CH4 selectivity and increased C5+ selectivities of the Fe catalyst. The Fe/S ratio, which can be used to define the poisoning ability of sulfur for the iron catalyst, was quantified based on the deactivation data obtained. The Fe/S ratio strongly depended on temperature and decreased remarkably with increasing temperature. At 270 °C one sulfur atom was found to eliminate ∼6 surface Fe atoms, and the ratio increased to 7.2 at 260 °C and increased further to 13.5 at 230 °C. The Fe/S relationship with increasing temperature is in good agreement with sulfur sorption theory. The changes in FTS and WGS rates of the Fe catalyst by sulfur were also studied. The decreases in rates of the two reactions were nearly the same. The results of XRD and Mossbauer spectroscopy indicated that the online addition of sulfur did not greatly alter the distributions of iron carbide and magnetite. Both data sets consistently suggest an adsorption mechanism, in line with the results of reaction testing. XANES results at the S K-edge further confirmed sulfur adsorption, and some sulfide and sulfate species, likely confined to the surface zone, were detected. In this study, the sulfur tolerances of the precipitated Fe and a supported Co catalyst were compared at an identical temperature (i.e., 230 °C), and similar M/S ratios (13.5–15.0) were obtained.

The effect of solvent on the hydrogen-deuterium isotopic homomolecular exchange over a traditional Fischer-Tropsch cobalt catalyst (25 % Co/Al2O3) was investigated using a plug flow reactor at two different reaction temperatures (room temperature (26 °C) and –20 °C) and at atmospheric pressure. In this study, three different solvents were tested, including n-pentane, n-hexadecane, and C-30 oil. The consumption of H2 and D2 is the same, and the concentration of the HD produced is twice the consumption of H2 or D2 at dry (without solvent) conditions. At room temperature and at –20 °C, conditions without solvent exhibited 100 mol% exchange with the formation of H2:HD:D2 having a 1:2:1 ratio. For n-pentane solvent, the exchange rates were ∼97 and ∼80 mol% at 26 and −20 °C, respectively. For the n-hexadecane and C30 oil solvents, the initial exchange rate was ∼50 mol%, with the exchange rate decreasing over time. The lower exchange rate with the n-hexadecane and C30 oil solvents, and also n-pentane at –20 °C, is likely due primarily to the limited mobility of reactant molecules in the liquid-filled pores of the catalyst. Blocking or covering of the pores of the catalyst depends on the molecular mass and density of the solvent. No isotopic partitioning preference was observed at two different temperatures and various solvents for the active cobalt catalyst.