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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.

The effect that sodium has on Pt/m-ZrO2 catalyst was investigated during ethanol steam reforming (ESR). Sodium doping decreases the catalytic activity, but significantly increases CO2 selectivity, providing a means of improving H2 selectivity. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) results suggest that acetate species are intermediates in the reaction and that their decomposition can follow different routes depending on the catalyst formulation. When Pt/m-ZrO2 is promoted by sodium, decarboxylation is the favored route: forward decomposition of acetate at lower temperatures yields essentially methane and adsorbed carbonate, further decomposing to carbon dioxide. At higher temperature, the methane precursor can be intercepted by the metal for further steam reforming or a separate methane steam reforming catalyst can be used downstream. Decarbonylation is instead favored for the unpromoted catalyst; decarbonylation tends to lower the H2 selectivity of the overall process. Finally, the addition of sodium promotes C–C scission as methane formation is detected at lower temperature by DRIFTS and TPD-MS of ethanol in steam. This is analogous to formate C–H bond breaking in methanol steam reforming, steam-assisted formic acid decomposition, and water-gas shift reactions. In catalytic testing of ESR utilizing a tubular reactor at low temperatures (where steam reforming of CH4 is limited), methane and CO2 selectivities are higher with the Na-promoted catalyst than with the unpromoted catalyst. Thus, promotion of the forward decomposition of acetate route by Na addition is confirmed.

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.

The effect of support type (SiO2, CeO2, ZrO2, TiO2, Nb2O5) on the removal of the different oxygenated functional groups (hydroxyl and methoxy) was investigated in the hydrodeoxygenation (HDO) of guaiacol over supported Pd catalysts at 573 K and atmospheric pressure. The product distribution depended on the support type, and three main reaction pathways were proposed: demethoxylation, demethylation and dehydroxylation. Demethoxylation yielding phenol was the dominant reaction pathway over all catalysts with only a minor contribution from the demethylation reaction taking place. However, significant dehydroxylation reaction was still observed for the catalysts having Pd supported on ZrO2, TiO2 and Nb2O5. Further conversion of phenol to cylohexanone was favored over SiO2 and CeO2-based catalysts, while benzene was only detected over ZrO2, TiO2 and Nb2O5, which is due to the presence of oxophilic cations. DRIFTS measurements were carried out to evaluate the adsorption mode and strength of guaiacol on the catalyst surface. The functional groups involved in adsorption of guaiacol included both hydroxyl and methoxy groups. At the reaction conditions, the hydroxyl group is strongly adsorbed to the catalyst surface and may block the catalytic sites, thus inhibiting further conversion of phenol and resulting in lower deoxygenation rates.

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.

Recently, Honda Research USA, Inc. and the University of Kentucky Center for Applied Energy Research researchers showed that Na doping of Pt/ZrO2 catalysts can significantly improve the rate of water-gas shift (WGS). This was attributed to the electronic weakening of the carbon–hydrogen (C–H) bond of formate, with formate being the suggested intermediate of an “associative mechanism.” In this work, we sought to determine (1) how the Na dopant loading affects the steam-assisted formate decomposition and WGS reaction rates and (2) the nature of the electronic effect that weakens the C–H bond of formate as a function of Na dopant loading. We observed that doping Na to up to 1% by weight slightly increased the density of defect-associated bridging hydroxyl groups, which are active sites for producing formate from CO. However, at 2.5% Na, the optimum loading, there was a distinct step-change shift of the band corresponding to C–H stretching of formate to lower wavenumbers, consistent with bond weakening. Pt-carbonyl bands were still able to form at this loading, indicating the availability of Pt sites for dehydrogenating formate during H2O-promoted formate decomposition. At 5% Na loading, while the formate C–H band remained at lower wavenumbers, Pt-carbonyl bands were severely attenuated, indicating a lack of availability of Pt metal sites at the higher loading. Thus, both steam-assisted formate decomposition and low-temperature WGS rates reached maxima at an optimum Na dopant loading of 2.5% Na. The results suggest that the transition state of formate decomposition involves H2O, with Pt assisting by providing a porthole for H2 removal, and with Na exerting a weakening effect on the formate C–H bond. The cleaving of this bond is the proposed rate-determining step of the cycle.

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.

The purpose of this investigation was to examine the effect of sulfur impurity on 1%Pt/KL-zeolite catalyst by co-feeding 500 ppbv hydrogen sulfide (H2S) during hexane aromatization under industrially relevant conditions using a plug flow reactor. Product selectivity and hexane conversion were measured with time-on-stream and compared to a clean run carried out under otherwise identical conditions. Sulfur addition to the feed accelerated the rate of deactivation as observed by rapid declines in both hexane conversion and benzene selectivity; hexene selectivity, the product of the less structurally sensitive dehydrogenation reaction, increased significantly. After 20 h, which was enough time to observe sufficient deactivation, the reaction was stopped. For the purpose of catalyst characterization, after cooling to 150 °C, the catalyst was preserved in Polywax 725 to prevent catalyst oxidation. XANES analysis at the potassium K-edge suggests that the local environment for potassium was not significantly altered by sulfur addition, while sulfur K-edge results indicate that sulfur bound to platinum to form platinum sulfide (PtS, not PtS2). Platinum sulfide is likely responsible for accelerating Pt growth, as observed in DRIFTS of adsorbed CO and HR-TEM/STEM micrographs.

A detailed kinetic model of Fischer–Tropsch synthesis (FTS) product formation, including secondary methane formation and 1-olefin hydrogenation, has been developed. Methane formation in FTS over the cobalt-based catalyst is well known to be higher-than-expected compared to other n-paraffin products under typical reaction conditions. A novel model proposes secondary methane formation on a different type of active site, which is not active in forming C2+ products, to explain this anomalous methane behavior. In addition, a model of secondary 1-olefin hydrogenation has also been developed. Secondary 1-olefin hydrogenation is related to secondary methane formation with both reactions happening on the same type of active sites. The model parameters were estimated from experimental data obtained with Co/Re/γ-Al2O3 catalyst in a slurry-phase stirred tank reactor over a range of conditions (T = 478, 493, and 503 K, P = 1.5 and 2.5 MPa, H2/CO feed ratio = 1.4 and 2.1, and XCO = 16–62%). The proposed model including secondary methane formation and 1-olefin hydrogenation is shown to provide an improved quantitative and qualitative prediction of experimentally observed behavior compared to the detailed model with only primary reactions.

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.

This work aims at investigating the effect of the type of metal (Pt, Pd, Rh, Ru, Cu, Ni, Co) on the performance of ZrO2-supported catalysts for the hydrodeoxygenation of phenol in the gas phase at 573 K and 1 atm. Two different reaction pathways take place depending on the type of the metal. For Pt/ZrO2 and Pd/ZrO2 catalysts, phenol is mainly tautomerized, followed by hydrogenation of the C=C bond of the tautomer intermediate formed, producing cyclohexanone and cyclohexanol. By contrast, the direct dehydroxylation of phenol followed by hydrogenolysis might also occur over more oxophilic metals such as Rh, Ru, Co, and Ni. In addition to the metals, the oxophilic sites of this support represented by Zr4+ and Zr3+ cations near the perimeter of the metal particles also increased the selectivity to deoxygenated products. All catalysts were significantly deactivated mainly owing to the growth of metal particle size and the decrease in the density of oxophilic sites.

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 influences of nitric acid treatment on a carbon nanotube (CNT) support and the preparation method, incipient wetness impregnation (IWI) versus chemical vapor deposition (CVD), on catalytic performance during Fischer–Tropsch (FT) synthesis were examined using a slurry phase reactor. Acid treated CNT (ACNT) supported Ru catalysts exhibited higher activities compared to Ru supported on untreated CNTs (UCNTs). The acid-treated CVD catalyst had higher initial CO conversion (smaller average Ru particle size) but sintered more due to a greater tendency for Ru to be deposited exterior to CNT channels relative to IWI. After the initial decline and leveling off period, the ACNT IWI catalyst had the highest steady activity among the catalysts tested. The ACNT IWI catalyst also displayed greater oxygenate selectivity (∼17%) compared to ACNT CVD (∼12%) and UCNT IWI (∼10%) catalysts at similar conversions. Acid treatment created adsorption sites on the CNT surface that anchor Ru precursors and promote CO insertion ...

Conversion of bio-oil from flash pyrolysis of biomass is a way to produce useful renewable feedstocks for the chemicals industry. Dehydration of pentanediol (1,5- and 2,4-pentanediol) was investigated over CeO2, CeO2-Ga2O3, and CeO2-In2O3 catalysts at 250–350 °C. Adding Ga or In (20 mol%) improved the conversion of pentanediol over CeO2, but adversely affected selectivity. In the base case, 1,5-pentanediol was converted on CeO2 to 4-penten-1-ol and 1-pentanol, desired linear alcohols, together with unwanted cyclopentanol and cyclopentanone byproducts. Adding gallium or indium to ceria increased the selectivity towards undesired cyclized products like tetrahydropyran and tetrahydropyran-2-one due to increased acidity. In the base case, 2,4-pentanediol converted on CeO2 to unsaturated alcohol (e. g., 3-penten-2-ol > 74 % selectivity), but adding Ga or In promoted acid-catalyzed cracking. Tuning the acid-base characteristics of ceria significantly alters the product distribution.