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The valorization of waste biomass is a resource for the current energy transition and a pillar of circular economy. In particular, the short-term evolution of the mobility sector requires a suitable green liquid fuel, especially for aviation and shipping market. Pyrolysis is a promising technology to convert lignocellulosic biomass into valuable fuels and chemicals, but several negative features of bio-oil (poor stability, acidity, coking tendency, high oxygen content) limit both its direct use and its upgrading processes. These negative factors are mainly caused by the presence of C2-C4 oxygenates in bio-oil (aldehydes, ketones, acids). A possible solution to improve bio-oil quality is the addition of a catalytic upgrading stage, aiming to convert these detrimental light oxygenates from the vapor-phase. C-C coupling reactions - like ketonization and aldol condensation - can increase the C-chain length of bio-oil species while reducing the overall O/C ratio. Catalysis is necessary to improve the kinetics (rate and selectivity) of these processes. In this work, acetic acid chain-growth reactions are studied on TiO2 and Ru/TiO2 catalysts, proving relevant performances in promoting not only ketonization but also secondary growth reactions with the formation of C8+ species. [ABSTRACT FROM AUTHOR]

The reduction by H2 of nitrates stored on a model Pt–Ba/Al2O3 catalyst under isothermal conditions was investigated. An in-series two-step process involving at first the formation of ammonia on reaction of nitrates with H2 (step 1), followed by the reaction of ammonia with residual stored nitrates to give N2 (step 2) is proposed. Different temperature thresholds for the two steps are identified, with step 1 being much faster than step 2. The reaction of ammonia with nitrates to give nitrogen (step 2) is very selective, is rate-determining, and represents the major route for nitrogen formation. Due to the fast reduction of adsorbed nitrates by hydrogen (step 1) and to the “plug-flow” integral behavior of the reactor, an H2 front develops that travels along the reactor. Ammonia is readily produced at the front; if the temperature is high enough, then the regeneration process continues downstream of the hydrogen front due to the reaction of NH3 with the stored nitrates, leading to N2 production. This fully explains the change in product distribution with time observed at the reactor outlet during regeneration of LNT catalysts, as well as the effect of temperature on the selectivity of the process. The effects of water and CO2 on the reduction process also are addressed. Water favors the first step of the reduction process but has no significant impact on the subsequent reaction of ammonia with stored nitrates, whereas CO2 has a strong inhibiting effect both on the reduction of nitrates to ammonia by H2 (step 1) and on the subsequent reaction of ammonia with the residual stored nitrates (step 2), due to poisoning of Pt by CO. [Copyright &y& Elsevier]

Abstract: The effect of sulphur poisoning (in the range 0–2000ppm) on the characteristics and catalytic performances in the Fischer–Tropsch synthesis (FTS) of a bench-scale alumina supported cobalt catalyst is investigated in this study. It is found that sulphur did not lead to appreciable variations in the catalyst morphological characteristics; however, the catalyst reducibility/hydrogenating capability is significantly modified upon increasing the sulphur loading. The comparison between the catalytic performances of the sulphured samples pointed out that the presence of sulphur remarkably affected the productivity and the selectivity of the reaction. In particular for low S amounts (<100ppm) the CO conversion is decreased whereas the product distribution is not significantly affected; at higher S loadings a significant decrease in the formation of heavier products is observed along with a decrease in CO conversion. This leads to significant changes in the selectivity of the reaction. These effects have been tentatively associated with different effects of sulphur on the catalyst active sites, i.e. on the sites (or site ensembles) responsible for CO hydrogenation and for the chain growth processes. Finally, the experimental data of CO conversion decay with S-loading were nicely described according to a simple deactivation model which implies a strong effect of sulphur on the catalyst active sites. [Copyright &y& Elsevier]

The reduction process of NOx species stored over Pt-Ba/Al2O3 Lean NOx Trap systems is analysed in this paper when H2 is used as a reductant. The effect of different experimental conditions (temperature, reductant concentration, adsorption lengths, etc.) is addressed and discussed in relation to the selectivity and the efficiency of the reduction process. [ABSTRACT FROM AUTHOR]

Abstract: Mechanistic aspects of the reduction of stored NO x with hydrogen were analyzed over model Ba/γ-Al2O3 and Pt–Ba/γ-Al2O3 LNT trap catalysts and over a Ba/γ-Al2O3–Pt/γ-Al2O3 physical mixture. NO x species were stored and stabilized at 350 °C under controlled conditions, and their stability/reactivity was then analyzed under different atmospheres (He and hydrogen) either at constant temperature or with temperature programming under nearly isothermal conditions, that is, in the absence of significant thermal effects. The collected data indicate that over the Pt–Ba/Al2O3 catalyst, the reduction of stored NO x occurs at temperatures below those corresponding to their thermal stability. This indicates that the reduction of stored nitrates occurs in typical NSR catalysts according to a Pt-catalyzed surface reaction, which does not involve the thermal decomposition of the adsorbed NO x species as a preliminary step. The occurrence of such a pathway also requires the co-presence of the storage element and of the noble metal on the same support, because this route does not operate when they are dispersed on different support particles. [Copyright &y& Elsevier]

The one-pot CO 2 hydrogenation to lower olefins involves the integration of two catalytic reactions in a single reactor: the conversion of CO 2 into methanol (CTM) and its subsequent conversion into lower olefins (MTO). This approach requires two catalysts cooperating in the same reactor, posing different challenges in terms of synergies and interactions between the two active phases. In this work, we investigate the effect of process conditions and arrangements between In 2 O 3 -ZrO 2 (CTM catalyst) and SAPO-34 (MTO catalyst) on the lower olefins yield. We show that the distance between CTM and MTO active sites, studied by assessing different catalyst arrangements spanning from an intimate mixture obtained through mortar mixing to a complete segregation of the catalysts (i.e., consecutive beds), plays a key role in driving the products distribution. However, the thermodynamic equilibrium of the reverse water gas shift limits CO 2 conversion in the investigated conditions. Finally, we discuss the stability of the catalytic performances: the characterization of the spent samples after ∼400 h on stream indicated the deactivation of the catalytic materials in all investigated cases, with In sintering on the methanol catalyst, and SAPO-34 losing both P and Al due to hydrothermal aging; indications of In migration on SAPO-34 were also observed when the two catalyst are in contact. [Display omitted] • The mixture of In 2 O 3 -ZrO 2 and SAPO-34offers the highest olefin yield. • CO is the main product when the contact between catalysts is too loose or too close. • Higher SAPO-34 mass enhances hydrocarbon production, but lowers the olefin content. • The thermodynamic equilibrium of the RWGS limits CO 2 conversion. • Both In 2 O 3 -ZrO 2 and SAPO-34 show deactivation at the investigated conditions. [ABSTRACT FROM AUTHOR]

Abstract: The reactivity of selected alkaline (Na, K, Cs) and alkaline-earth (Ca, Ba, Mg) oxide catalysts in the oxidation of a model soot sample (Printex U) is investigated in this study. With the aim of obtaining information about the intrinsic reactivity of these elements, samples have been prepared in which the active elements have been directly deposited on the soot (“full contact” conditions). In this way the reactivity of the catalytic elements is not controlled by the type of contact with the soot. It is found that the combustion of soot is greatly enhanced by the presence of either alkaline or alkaline-earth oxides, with Cs and Mg exhibiting the highest and the lowest activity, respectively. Notably, the reactivity in the soot combustion is found to nicely correlate with the electropositivity of the investigated metal ions, in line with literature indications pointing out the relevance of the electron-donor characteristics of the active elements. The correlation between electropositivity and activity in the soot combustion is not apparent in the absence of a close contact, i.e. under loose contact conditions. Under these conditions it is suggested that the catalytic activity is governed by the mobility of the surface species, which favors the soot–catalyst contact. Accordingly the poor performances observed in the case of the alkaline-earth metal oxides suggest for these elements a poor mobility of the active surface species, as opposite to alkaline oxide based catalysts showing a high reactivity even under loose contact conditions. [Copyright &y& Elsevier]

Abstract: The potentiality of a typical Pt–Ba/Al2O3 NSR catalyst in the simultaneous removal of particulate matter (soot) and NO x is investigated in this work, and compared with that of a Pt/Al2O3 sample. The behaviour of the catalyst in the soot combustion and NO x removal has been separately analyzed by means of temperature programmed oxidation (TPO) experiments, isothermal combustions and transient response method (TRM), respectively. The results show that in presence of only oxygen, soot oxidation occurs slowly even at a temperature as high as 400°C. On the other hand, the presence of NO greatly increases the rate of soot conversion, which becomes significant at 350°C. The capability of the Pt–Ba/Al2O3 and Pt/Al2O3 catalysts to accomplish the removal of NO x in the absence and in the presence of soot was investigated under cycling conditions, i.e. alternating lean-rich phases according to the typical NSR strategy. It has been found that the Pt–Ba/Al2O3 sample is able to simultaneously remove both soot and NO x , as opposite to the Pt/Al2O3 catalyst which effectively performs the soot oxidation but is not able to remove gas phase NO x to a significant extent. The presence of soot does not significantly affect the activity in the NO x reduction of the Pt–Ba/Al2O3 catalyst. The comparable level of activity in the soot combustion which is observed between the Pt/Al2O3 and the Pt–Ba/Al2O3 sample in spite of the fact that the ternary sample accomplishes the removal of NO x in the gas phase has been tentatively ascribed to specific oxidizing properties of the stored nitrate species. [Copyright &y& Elsevier]

• NO adsorbs as nitrosyls over Pd/FER. • NO displaces CO from Pd sites. • Pd/FER zeolite store NO at 80 °C. A Pd-doped FER zeolite sample is synthesized and investigated for potential use in the low-temperature NO x adsorption. The catalyst is characterized by BET, XRD, TEM, NaCl titration and by in-situ FT-IR spectroscopy following adsorption of CO, NH 3 and NO for the characterization of the Pd sites. Over the calcined sample, Pd is present mainly as PdO x clusters/particles; near 13 % of Pd is present in the form of isolated ions. The NO x adsorption / desorption performances at low temperature are investigated by microreactor studies and operando FT-IR upon NO/O 2 adsorption followed by TPD under relevant operating conditions, i.e. in the presence of water and carbon dioxide. It is found that NO adsorbs in the form of Pd nitrosyls (hydrated and anhydrous) and nitrates; near 59 μmol/g cat of NO x could be adsorbed, corresponding to a NO/Pd ratio near 0.6. Upon heating, nitrosyls decompose and transform into anhydrous species leading to NO desorption in the low-T region (below 200 °C) and at higher temperature, with maximum near 370 °C. The presence of CO negatively affects the NO x storage capacity, due to a competition of CO and NO over the Pd storage sites. [ABSTRACT FROM AUTHOR]

• The calcined catalyst is completely reduced only after H 2 -reduction at 400 °C. • Passivation with 1%O 2 /He formed a thin CoO layer surrounding the metallic core. • The catalyst temperature increases with the O 2 -flow rate thus leading to CoO sintering. • The passivated catalyst is fully reduced even at 300 °C. • The passivated catalyst shows the same FTS performances of the calcined catalyst. Passivation of reduced cobalt-based catalysts is required prior to air exposure due to the exothermicity of the Co metal oxidation, which may lead to a significant increase of the temperature of the catalyst resulting in its degradation and in a potential fire hazard. This work shows the results of the passivation process carried out on a Pt-promoted Co-based catalyst supported on stabilized alumina at different space velocities in the range of 5–50 Ncc/min/g cat and constant O 2 concentration of 1 vol.%. Increasing the O 2 flow fed to the reactor, the specific amount of O 2 consumed on the catalyst slightly decreases. Around 30% of Co metal particles are oxidized to CoO species in all the passivation treatments. These species are found to be much more reducible than the Co oxides species present on the calcined catalyst. Indeed, all the passivated catalysts are completely depassivated at a temperature which is significantly lower (300 °C) than that needed to fully reduce the calcined catalyst (400 °C). The temperature of the catalyst almost linearly increases with the increase of the O 2 feed flow. Indeed, an abrupt increase of the catalyst temperature is observed for high O 2 flows, resulting in a decrease of the Co° dispersion (i.e. increase of the average Co° crystallites size) after depassivation. This result is explained with the onset of sintering phenomena of the CoO species formed during passivation. The passivation treatment is found to be unsuitable for long-term catalyst protection, since a deep re-oxidation of the passivated catalyst is observed after two months of air exposure. The effectiveness of the catalyst passivation is eventually validated by running FT reactivity tests at industrially relevant process conditions. The activity of the calcined catalyst reduced in-situ at 400 °C is compared to that of the same catalyst reduced ex-situ at the same temperature, passivated at low O 2 flow and depassivated in-situ at 300 °C. Interestingly, similar stability and reactivity, expressed both in terms of activity and selectivity, are obtained. [ABSTRACT FROM AUTHOR]

• Ru-based catalysts show stable and high performance during CO 2 methanation. • A gradual deactivation is observed during CO/CO 2 methanation at low temperatures. • Stable performance is observed during CO/CO 2 methanation at high temperatures. • Deactivation is due to strong CO adsorption and formation of inhibiting species. The reactivity of Ru/Al 2 O 3 catalysts in the hydrogenation of CO/CO 2 gas stream is investigated in this work to assess the possibility of carrying out CO 2 methanation even in the presence of CO in the feed stream. Such a goal is pursued by conducting reactivity studies at process conditions of industrial interest (i.e., at high CO x per-pass conversion and with concentrated CO x /H 2 streams) and by monitoring the surface species on the catalyst through transient DRIFTS-MS analysis. The catalyst shows gradual deactivation when the methanation is carried out in the presence of CO in the gas feed at low temperatures (200–300 °C). However, stable performance is observed at higher temperatures, showing CH 4 yields even higher than those observed during methanation of a pure CO 2 feed. DRIFTS-MS experiments agree with a CO 2 methanation pathway where CO 2 is adsorbed as bicarbonate on Al 2 O 3 and successively hydrogenated to methane on Ru, passing through formate and carbonyl intermediates. In the presence of CO at low temperature, the catalyst shows a higher CO coverage of the Ru sites, a larger formate coverage of the alumina sites and the presence of adsorbed carbonaceous species, identified as carboxylate and hydrocarbon species. By carrying out the CO 2 hydrogenation on the deactivated catalyst, carboxylates remain on the surface, effectively blocking CO 2 adsorption sites. However, the catalyst deactivation at low temperature is reversible as thermal treatment (>350 °C) is able to restore the catalytic activity. Notably, working above the carboxylate decomposition temperature ensures a clean catalyst surface without high CO coverage, resulting in stable and high performance in CO/CO 2 methanation. [ABSTRACT FROM AUTHOR]

Foregoing calcination and utilizing direct reduction of cobalt nitrate led to the formation of smaller cobalt oxide nanoclusters in stronger interaction with silica support as intermediates of the activation process to Co° nanoparticles; this was demonstrated by TPR, TPR-MS, TPR-XANES, and TPR-EXAFS experiments using hydrogen. These intermediate cobalt oxides included a spinel (e.g., Co 3 O 4 ) formed from oxidation of Co 2+ species by NO 2 , which in turn converted to CoO prior to formation of the metal. To improve the reducibility, metal promoters such as Pt, Re, Ru, and Ag were added. Hydrogen chemisorption and EXAFS experiments revealed smaller nanoparticles; Co-Co metal coordination numbers were significantly lower for the H 2 -activated Co metal nanoparticles when direct reduction of the nitrate was used relative to H 2 -activated air calcined catalysts. Comparing at the same space velocity, the best catalysts were Re and Pt promoted 12%Co/SiO 2 catalysts utilizing direct reduction of the nitrate, where initial conversions in a CSTR were up to 3.8 times higher and 71% higher than unpromoted and Pt promoted air calcined catalysts, respectively. At these conditions, methane production was lower (6.8 and 8.0% for Re and Pt promoted catalysts, respectively, by direct reduction versus 12.5 and 10.1% for unpromoted and Pt promoted air calcined catalysts) and C 5+ selectivity was higher (81.2% and 81.5% for Re and Pt promoted catalysts, respectively, by direct reduction versus 73.4 and 78.8% for unpromoted and Pt promoted air calcined catalysts). The uncalcined catalysts were slightly less stable than the calcined samples, with the only exception being the rhenium promoted sample, where no visible deactivation was observed; this catalyst also had the highest catalytic activity on a per gram catalyst basis. [ABSTRACT FROM AUTHOR]

The promoting effect of Mn and Zn on the performance of Fe-based catalysts has been comparatively investigated in the COx hydrogenation to heavy hydrocarbons in the presence of H2-deficient streams. To this scope, two catalysts have been prepared by coprecipitation, followed by impregnation with Cu and K, and tested at 220 °C and 30 barg after an activation treatment with syngas. Both catalysts have been found to be active and selective to long-chain hydrocarbons in the presence of either H2/CO or H2/CO2 mixtures. Despite lower catalyst reducibility, the presence of Zn has resulted in higher COx conversion rates. Furthermore, the Zn-promoted catalyst converted COx into heavier and less-saturated hydrocarbons. These results are consistent with a role of Zn in promoting the catalyst basicity, which is a key property to keep low the superficial H/C ratio and to slow chain termination reactions as well as secondary olefin hydrogenations. [ABSTRACT FROM AUTHOR]

The performances of representative Co-based and Fe-based Fischer-Tropsch catalysts have been comparatively investigated in the hydrogenation of CO and CO 2 . Over an un-promoted Co/γ-Al 2 O 3 catalyst, CO 2 is easily hydrogenated and its conversion rate is even faster than that of CO; however, the selectivities of the two processes are extremely different, with methane largely dominating the product distribution in the case of CO 2 hydrogenation and long-chain hydrocarbons dominating the products pool during CO hydrogenation. As opposite to cobalt, CO 2 hydrogenation rate over K-promoted 100Fe/10Zn/1Cu (at/at) catalysts is slower than that of CO, but the products are dominated by middle distillates when CO 2 replaces CO in the feed. Such behaviors depend on the different adsorption strengths of CO and CO 2 , which affect the H/C atomic ratio on the catalyst surface. In the case of Fe-based catalyst, we have also found that the catalytic sites active in the chain growth process (iron carbides) are transformed into sites active in the hydrogenation reactions (iron oxides/reduced iron centers) at low CO partial pressures. Potassium has a key role in promoting the stability of chain growth sites, thus decreasing the secondary reactions of olefins. [ABSTRACT FROM AUTHOR]

In this work, the kinetics of the NH 3 /NO/O 2 reacting system over V 2 O 5 –WO 3 /TiO 2 catalysts was studied under conditions of NH 3 /NO ratio ≥ 1 and temperature up to 400 °C, where some ammonia oxidation is expected. NH 3 -SCR and NH 3 -oxidation tests were performed over powdered catalysts, at varying V-loads. Over a high V-load home-made catalyst, NO conversion passed through a maximum at increasing temperature, as commonly observed in SCR tests at the onset of ammonia oxidation; however, since the experiments were performed under excess ammonia, the high temperature decrease of NO conversion could not be associated with a lack of surface NH 3 . The experiments were interpreted as the evidence of an unselective NH 3 -oxidation route, giving rise to some NO production. NH 3 -oxidation tests, though, showed low selectivity to NO (which is in line with the current literature); however, a quantitative analysis of data showed that the observed product distribution is fully in line with an indirect-consecutive reaction scheme from NH 3 to N 2 , wherein NO is formed by NH 3 oxidation and is then rapidly converted to N 2 via NH 3 -SCR. The kinetic investigation was extended to commercial catalysts with low and medium V-loads. NH 3 -SCR tests showed increasing trends of NO conversion with temperature within the range 250–400 °C, thus they did not show any clear evidence for NH 3 oxidation. However, NH 3 -oxidation tests showed that the reaction was active above 350 °C; notably, over 95% selectivity to N 2 was observed. A quantitative analysis of the NH 3 -oxidation tests, based on the independent estimate of the intrinsic rate of NH 3 -SCR, showed that the observation of few ppm NO slip is fully in line with the assumption of a two-step kinetic scheme. A reaction path analysis shows that by neglecting the unselective nature of ammonia oxidation on V-catalysts the rate of this reaction is overestimated by a factor of 2. Preliminary evaluations suggest that the impact of NH 3 -oxidation on the integral performance of monolith reactors (operating at NH 3 /NO ratios close to 1) is non negligible, so that the correct identification of the reaction stoichiometry is crucial. [ABSTRACT FROM AUTHOR]

Abstract: The behavior of a model PtBa/Al2O3 model NSR catalyst in both the NO x storage/reduction and soot oxidation is investigated in this work. It is found that the presence of soot negatively influences the NO x storage capacity of the catalyst, evaluated at 623K in presence of water and CO2 in the feed stream: in fact the amounts of NO x stored in presence of soot decrease by nearly 30% in the presence of roughly 10% (w/w) of soot. The presence of soot has a destabilizing effect on the NO x adsorbed species, which decompose to a large extent in the absence of gas phase NO and oxygen. This has also been confirmed by dedicated TPD and TPO experiments. However the presence of soot does not appreciably affect the behavior of the PtBa/Al2O3 catalyst in the reduction by H2 of the stored nitrates, being in all cases N2 the major reaction product along with minor amounts of ammonia. During the storage of NO x , soot oxidation takes place. Notably, the stored NO x participate in the soot oxidation upon release of NO2 and O2 which actively oxidize soot. However a direct participation of the adsorbed NO x species in the oxidation of soot cannot be excluded. [ABSTRACT FROM AUTHOR]

Abstract: The role of palladium precursors and the preparation route in the catalytic properties of PdO/Al2O3 catalysts toward methane oxidation was investigated in this paper. The catalysts were prepared using palladium chloride, nitrate and acetylacetonate as precursors and the preparation routes employed were impregnation of alumina with solutions of these precursors and the polyol method, in which palladium deposition is carried in a liquid polyol, e.g. ethylene glycol. All catalysts were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), transmission electron microscopy (TEM), surface area measurements and temperature programmed desorption of O2 (TPD). Unsteady-state methane oxidation was carried out by temperature-programmed surface reaction (TPSR). The results obtained suggested that the use of different palladium precursors and preparation routes played an important role on the properties of the catalysts, as palladium particle size, thermal stability of PdO and catalytic properties toward methane combustion. The use of palladium acetylacetonate as precursor by the impregnation method generated well-dispersed PdO particles on alumina. Regarding the PdO thermal stability and the activity toward methane combustion, this catalyst also presented the highest thermal stability and catalytic activity. [Copyright &y& Elsevier]

[Display omitted] • Impregnation of a V/Mo/Ti commercial catalyst with HCl enhances the intrinsic DeNOx rate by a factor of 5. • NO + O 2 adsorption is remarkably enhanced. • NH 3 adsorption capacity and strength is negligibly affected. • The HCl-doping reveals the rate limiting role of NO activation in NH 3 -SCR. NH 3 -SCR is the best available technology for NO x abatement from power plant, incinerators, gasifiers, and a well-established technology for on board NO x emission control; in the last 40 years, the reaction mechanism and kinetics have been deeply investigated, but the understanding of the nature of surface intermediates and rate determining steps is still object of a lively discussion. A major factor, though, has been largely neglected in the scientific literature, that is the presence of HCl in the flue gases generated by coal, biomass and plastics. In this work, the effect of HCl on NH 3 -SCR over V 2 O 5 catalysts was investigated through combined kinetic analysis and operando FTIR. Unexpectedly, after HCl-doping, the catalyst intrinsic activity of a commercial catalyst increased by a factor of 5. Besides, it was found that while the NH 3 surface coverage is little affected by HCl-doping, the chemisorption capacity of NO + O 2 undergoes a remarkable promotion that scales with the promotion of the reaction rate. The HCl-effect provided thus an indirect but unambiguous piece of evidence that NO-activation by an O-species is a key rate controlling step of NH 3 -SCR. [ABSTRACT FROM AUTHOR]