The catalytic oxidation of different volatile organic compounds (VOCs) has been widely studied for several decades within the field of air depollution. However, there is still much to understand regarding the effects that these VOCs have on each other when they are blended together in the reaction mixture, as would be expected in many emissions. Herein, the catalytic oxidation of toluene and 2-propanol on supported manganese oxides under both single and binary VOCs oxidation conditions has been studied. We have found the catalyst activity for VOCs mineralization and its selectivity towards other by-products (i.e., acetone or propylene from 2-propanol) to be strongly dependent on the reaction conditions, the catalyst redox properties and support acidity. We have also assessed the promotion/inhibition effects derived from the VOCs mixture and proposed the reaction mechanism in each case by means of in-situ DRIFTS measurements.

In a previous study, a drastic enhancement of the NOx conversion in EtOH-SCR process was achieved by means of ammonia and ethanol co-feeding over Ag/Al 2 O 3 catalyst to avoid the NO 2 /NOx ratio dependency of conventional implemented urea-SCR technology. The ammonia activation was mainly attributed to the availability of hydrogen H* species resulting from EtOH dehydrogenation, which promoted the H 2 assisted NH 3 -SCR over Ag/Al 2 O 3 . Additional conversion gain was reached with a dual-bed configuration in which a NH 3 -SCR catalyst (WO 3 /Ce x Zr 1−x O 2 ) was added downstream to the silver-based sample (Ag/Al 2 O 3 + NH 3 -SCR catalyst). This study deals with the influence of the SCR catalyst formulation on the catalytic performances of the dual-bed system. Oxide-based sample (WO 3 /Ce x Zr 1−x O 2 ) and exchanged copper zeolite (Cu 2.5 –FER) were selected as model NH 3 -SCR catalysts. Results shows that WO 3 /Ce x Zr 1−x O 2 in more appropriate in dual-bed configuration for (EtOH + NH 3 )-SCR process because ammonia and ethanol (or its by-products) strongly interacted together on Cu 2.5 –FER.

The effect of the sodium addition mode was investigated on model Cu/FER selective catalytic reduction (SCR) catalysts with two copper loadings (2.8 wt. % and 6.1 wt. %) in order to compare samples with or without over-exchanged copper. Na was added by wet-impregnation using two solvents: water or ethanol. Catalysts were evaluated in Standard and Fast-SCR conditions, as well as in NO and NH3 oxidation. They were characterized by H2-TPR, NO and NH3 adsorption monitored by FT-IR. As expected, whatever the copper loading, ammonia adsorption capacity was decreased by Na additions. Interestingly, characterizations also showed that Na impregnation in water favors the migration of the Cu-exchanged species, leading to the formation of CuO extra-framework compounds. Consequently, for both copper loadings, Na impregnation in water led to a stronger catalyst deactivation than impregnation in ethanol. Finally, the NOx conversion at low temperature (250 °C) appeared mainly affected by the loss in NH3 adsorption capacity whereas the deNOx deactivation at high temperature (500 °C) was rather governed by the decrease in the exchanged copper ratio, which also induced a partial inhibition of NO and NH3 oxidation behaviors.

HNCO adsorption monitored by FT-IR spectroscopy was performed over a wide range of oxides from various acid-base and redox properties: SiO2, Al2O3, TiO2, ZrO2, CeO2, CeO2-ZrO2, WO3/CeO2-ZrO2. HNCO adsorbed dissociatively in the whole studied samples. A correlation with pyridine via wavenumbers revealed that HNCO dissociation mainly involved weak Lewis acid sites (LAS) location. The significant isocyanate adsorption capacity of titania and zirconia was evidenced. HNCO hydrolysis reaction was also investigated. Among the various studied samples, CeO2-ZrO2 and WO3/CeO2-ZrO2 presented the higher HNCO hydrolysis rate, with ammonia formation from room temperature. For all studied samples, -NCO groups were evidenced as intermediate species of HNCO hydrolysis.

An exceptional reactivity between NO2 and the reductant species was demonstrated during NO2-SCR experiments with urea, when only NO2 was used as NOx.

Since 2014 (Euro VI), heavy goods vehicles must be equipped with a complex exhaust gas post-treatment system including a diesel oxidation catalyst (DOC), a catalyst for the selective reduction of NO x (SCR), and a diesel particulate filter (DPF), with a required durability of 7 years or 700,000 km. Consequently, when biodiesel is used, especially pure biodiesel (B100), catalysts will be subjected over 700,000 km to kilogrammes of inorganic elements (Na, K, and P), even if they are limited to a few ppm in biodiesel fuel. The durability of the catalytic exhaust system is therefore questionable. This issue is of major concern to vehicle manufacturers. This study aims to make a detailed investigation of the impact of biodiesel use on the durability of the existing Euro VI catalytic systems, with a special focus on deactivation through poisoning for DOC and SCR catalysts, and on the physics and chemistry of particles and their reactivity.

The NOx selective catalytic reduction (SCR) is extensively studied as an effective process for air pollutants abatement from lean burn and Diesel vehicles. In the implemented Urea-SCR technology, the NO2/NOx ratio is a key parameter that limits the deNO(x) efficiency at low temperature (175-250 degrees C). We demonstrate that co-feeding of ammonia and ethanol on a Ag/Al2O3 catalyst enables a drastic enhancement of the NOx conversion at temperatures below 200 degrees C using only NO as NOx (standard SCR condition). Even if NO2 is provided at low temperature by the NO oxidation over Ag/Al2O3 in presence of EtOH, the NO. conversion improvement is not only due to a direct reaction between NH3 and NOx, but mainly attributed to the availability of hydrogen H* species resulting from EtOH oxidation (similar to a H-2 assisted NH3-SCR process). Due to the presence of remaining NH3 and NO2 (formed over Ag/Al2O3 catalyst), further deNO(x) efficiency improvement was obtained at low temperature by addition of a NH3-SCR catalyst (WO3/CeZr). The critical dependence of the SCR process on the Diesel Oxidation Catalyst (DOC) efficiency at low temperature is thus avoided. (C) 2017 Elsevier B.V. All rights reserved.

To treat the NOx emissions from diesel vehicles, NOx selective catalytic reduction (SCR) process by NH3 requires the use of a precursor: an urea aqueous solution. Using an innovative experimental synthetic gas bench adjusted to powdered catalysts and allowing the use of urea or ammonia, the competitive reactivity of the HNCO intermediate species was evidenced. This intermediate species was found to be highly reactive toward NO2, without NOx reduction. During the SCR process, a mix of both NO and NO2 was evidenced to react with HNCO and contribute to the NOx reduction efficiency, resulting in an original pathway.

In order to develop new NOx selective catalytic reduction (SCR) catalysts for automotive application, the DeNOx catalytic activity is commonly evaluate at the laboratory scale using NH 3 as reductant. However, NH 3 is not directly used on board: an ammonia precursor based on urea aqueous solution is injected in the exhaust pipe upstream the SCR catalyst. It is admitted that ammonia is then obtained by two successive reactions: the thermal decomposition of urea, leading to HNCO and NH 3 , and the HNCO hydrolysis, providing the second molecule of NH 3 . However, the complete availability of ammonia from urea could be not achieved before the SCR catalyst. Then, the influence of the SCR catalyst on these reactions may impact the NOx reduction efficiency. With the aim to study the possible role of the SCR catalyst on the ammonia availability, an innovative synthetic gas bench adjusted to powdered material was developed, allowing the direct comparison of the use of gaseous NH 3 or urea (injected aqueous solution) for the NOx conversion, depending on the temperature (200–500 °C). This work presents results obtained with an oxide based prototype SCR catalyst in comparison with a patented Fe-exchanged zeolite, evaluated in both standard and fast SCR stoichiometry. This study points out that, in contrast with the exchanged zeolite, the evaluated oxide based catalyst may not allow an optimal NOx conversion because of a lack in ammonia availability, attributed to insufficient activity in HNCO hydrolysis.

The efficiency and the selectivity of a model platinum based catalyst supported on a modified ceria-zirconia oxide was evaluated in the NO storage-reduction (NSR) process at four catalytic scales: powder, (0.5 '' x 1.5 '') flow-through monolith (FTM) system, small size (1 '' x 2 '') and full size (5.66 '' x 10 '') catalysed Diesel Particulate Filter (DPF).The washcoating of the active phase over FTM affects both the NOx storage properties and the NOx reduction step. The reduction step efficiency is especially decreased at low temperatures. It is associated with an incomplete regeneration of the storage sites and with a strong NOx desorption peak during the rich pulses of the NSR process for the FTM supported system. The NOx reduction selectivity is also strongly affected by the upscale, with an important N2O selectivity detected over FTM. The recorded NOx profiles during NSR cycles indicate a probable diffusion limitation. However, same trends were observed for both powder and FTM systems concerning the effect of the reductant mixture, for both NSR efficiency and N-compounds selectivity.After incorporation of the active phase in the porosity of the DPF, a sharp drop in NOx storage properties and subsequently in NSR efficiency are observed. Supplementary tests suggest that the diffusion from the platinum oxidizing sites to the storage sites is again very affected by the upscale. Finally, the engine bench tests confirm the low DeNO(x) activity of the DPF system. (C) 2014 Elsevier B.V. All rights reserved.

CoRe4 catalysts highly active for ammonia synthesis at ambient pressure and 400°C can be prepared without an ammonolysis stage. Pre-treatments under 3:1 H2:N2 and 3:1 H2:Ar atmospheres are shown to influence catalytic performance with the latter treatment leading to an induction period prior to development of activity upon switching to an ammonia synthesis feedstream. The difference in behaviour between the two pre-treatment atmospheres is manifested in temperature programmed nitrogen isotopic exchange experiments where H2:Ar treated material is inactive and its H2:N2 treated counterpart is active.

The NOx selective catalytic reduction (SCR) with ethanol has been investigated over alumina supported silver catalyst with a special attention to the main involved reactions depending on the temperature test. With this aim, the possible reducers from ethanol transformations were also evaluated (C 2 H 5 OH, CH 3 CHO, C 2 H 4 , CO). In addition, the contributions of the gas phase reactions and the alumina support were also pointed out. Based on the C-products and N-compounds distributions, it is assumed that at low temperature ( T < 300 °C), ethanol reacts firstly with NO + O 2 to produce acetaldehyde and N 2 . For higher temperatures, two reaction pathways have been proposed, supported by the CH 3 CHO-SCR results: a direct reaction between NO 2 and CH 3 CHO, or via –NCO species.

It was previously demonstrated in the first part of this work that NOx storage-reduction process over Pt/BaO/Al2O3 model catalyst is limited by the reduction step, with ammonia emission since H2 is not fully consumed. The stored NOx reacts preferentially with the introduced H2 giving NH3, than with NH3 in order to produce N2. Mn addition favors the NOx reduction with ammonia leading to better conversion and selectivity, but only at 400 °C. In Part II, a special attention was focused on the role of Ce and Mn–Ce addition in regard to the NOx conversion and the ammonia emission in the 200–400 °C temperature range. With ceria modified Pt/20Ba/Al catalyst, significant improvements are obtained from 300 °C. In addition to the enhancement of the NOx + NH3 reaction, the ammonia selectivity is maintained at a lower level compared with Pt/Ba(Mn)/Al catalysts, even in the case of a large H2 excess. It is attributed to the ammonia oxidation into N2 via the available oxygen at the catalyst surface. A synergetic effect is observed between Mn and Ce when they are added simultaneously in Pt/Ba/Al catalyst.

The ammonia selectivity during the cycling NOx storage reduction process over a model Pt/Ba/Al2O3 catalyst was studied. Firstly, it was demonstrated that, whereas the presence of water or carbon dioxide in the gas mixture have a negative effect on the storage step, the effect of these components have different impacts on the NOx efficiency. Due to their involvement in the reverse water gas shift (RWGS) reaction, the absence of water in the gas mixture leads to a drop of the NOx removal whereas without CO2, an increase of the NOx conversion is observed. It was also showed that the reducer (H2) conversion during the short excursion in rich condition is directly correlated to the NH3 emission. NH3 is emitted since hydrogen is not fully converted, whatever the NOx conversion rate. The ammonia pathway is clearly demonstrated and it was claim that, when H2 remains in the reaction mixture, the ammonia production rate is higher than the ammonia reaction with the remaining NOx in order to form N2.

This work deals with the effect of Mn or Fe addition on the NO x storage–reduction properties of a Pt/Ba/Al2O3 model catalyst. NO x storage capacity, SO2 poisoning and regeneration and NO x removal efficiency under rich/lean cycling conditions are studied. Fe addition to Pt/Ba/Al2O3 leads only to a small increase of NO x storage capacity, and more interestingly, to a better sulfur removal due to the inhibition of bulk barium sulfate formation. Unfortunately, the NO x storage property cannot be fully recovered. Moreover, Fe addition results in a decrease in the NO x removal efficiency. Mn addition also improves the NO x storage capacity, but no significant influence on the sulfur elimination is observed. Mn-doped catalyst does not improve the NO x removal efficiency, but NH3 selectivity is found to drastically decrease at 400 °C, from 20 to 3%. In addition, the NO x conversion can be improved at higher H2 concentration in the rich pulse, always keeping NH3 selectivity at low level.

The influence of the ceria-zirconia mixed oxide composition in Pt/CexZr1-xO2 catalysts was studied toward NOx storage capacity (NSC), including sulfur poisoning and sulfur regeneration, and NOx reduction efficiency in lean-rich cycling conditions. The results are compared with a Pt/Ba/Al model catalyst. The samples were characterized by N-2 adsorption, XRD and H-2-TPR. The behaviors of the ceriazirconia supported catalysts are quite similar whatever their composition. They are sensitive to a reducing pretreatment which leads to an increase of (i) the cerium reducibility/oxygen mobility, (ii) the NO oxidation rate and (iii) the NOx storage capacity at 300 and 400 degrees C. The sulfating treatment leads to a dramatic decrease of the NOx storage capacity for all catalysts, the decrease being more pronounced for the Zr-rich samples. H-2-TPR experiments show that the sulfates amount and their stability tend to increase with the Zr content, but these sulfates are significantly less stable compared with Pt/Ba/Al. The sulfur elimination rates in rich mixture at 550 degrees C are higher than 90% with the ceria-zirconia supported catalysts versus 56% with Pt/Ba/Al.The ceria-zirconia supported catalysts are able to convert NOx in lean-rich cycling condition. Compared with Pt/Ba/Al, the NOx conversions are a little lowered but the ammonia selectivity is significantly decreased with the Ce-Zr mixed oxides, with a beneficial influence of the cerium content. (C) 2009 Elsevier B.V. All rights reserved.

The influence of a pre-treatment at 700°C, either under a O2/N2 mixture or only under N2, and followed by a hydrothermal aging at 700°C under wet air, was studied for Pt/Ba/Al NSR model catalysts prepared by different methods: (i) successive impregnation of Ba and Pt, (ii) co-addition of Pt and Ba and (iii) barium precipitation followed by Pt impregnation. The catalysts were evaluated by NOx storage capacity measurements and were characterized by N2 adsorption, XRD, CO2-TPD, H2 chemisorption and H2-TPR. The pre-treatment under N2 largely improves the NOx storage performance in the whole studied temperature range (200–400°C), with or without H2O and CO2 in the inlet gas. The better NOx storage properties of the catalysts treated under N2 before aging are due to: (i) a higher NO oxidation activity (mainly linked to a higher platinum dispersion), (ii) a higher number of NOx storage sites resulting from a higher barium dispersion, and consequently to (iii) a higher Pt-Ba proximity.

The interaction and reactivity of model sulfur compounds with gasoline sulfur reduction additives based on Zn-, Na-, and F-doped γ-Al2O3 have been investigated by in situ and operando infrared spectroscopy and microactivity tests. While gasoline sulfur reduction additives selectively crack tetrahydrothiophene (THT) into H2S and butadiene they are inactive toward thiophene. When blended with a fluid catalytic cracking (FCC) catalyst, gasoline sulfur reduction additives do reduce (alkyl)thiophene contents in gasoline. There is a synergy between the FCC catalyst and the gasoline sulfur reduction additive leading to sulfur reduction. Under actual FCC conditions, Al2O3-based gasoline sulfur reduction additives reduce thiophenic compounds by decomposing (alkyl)THT formed via hydrogen transfer on the FCC catalyst. A balance between acid and base properties is required for an optimum activity of the additive, suggesting that THT cracking occurs on Lewis acid–base pairs through successive E2 eliminations.

The selective synthesis of phytosterol esters from natural sterols and methyl esters was investigated on new grounds by a chemical process using basic solids that are reusable, active, and more selective than the currently used homogeneous catalysts (e.g., alkali hydroxides, carbonates). Various lanthanum oxides with different synthesis procedures and varying specific surface areas were tested. The catalytic performance of the new solids and, more specifically, the ability of La2O3 oxides in increasing phytosterol ester selectivity, was correlated with their acido-basic properties, which were fully characterized by infrared spectroscopy. All La2O3 oxides involved surface carbonate species with different structural states and strengths, as revealed by propyne adsorption. The selectivity to phytosterol ester varied from 90 to 96%, confirming that the side reaction of dehydration of β-sitosterol was strongly inhibited. The phytosterol ester yield could reach 89% and was related to the basic strength of the carbonate species. The lower the carbonate basicity, the higher the phytosterol ester yield. Moreover, IR spectra of catalysts diluted in KBr powder showed that the higher the intensity of unidentate carbonate bands, the higher the yield. It was concluded that the synthesis of phytosterol esters from fatty methyl esters and sitosterols in the presence of La2O3 catalysts requires ionic carbonate species of medium basic strength.

Self-supporting molybdenum sulfide samples with high surface area were prepared by in situ thermal decomposition in vacuum of ammonium thiomolybdate. BET specific surface area of the resulting material has its highest values of about 120m2/g for samples treated in situ at 473K and decreases on further heating, while the composition of samples treated at 423–473K is close to MoS3, and after heating up to 573K corresponds to MoS2. FTIR spectra show that precursor decomposition is almost completed already after treatment at 423K, although the sample still contains admixed ammonium ions. After 473K most of contaminations are gone. Spectra of adsorbed NH3, ND3, CO, SO2, CO2, COS and CH3SH adsorbed on samples pretreated at 423–473K are very close to those obtained for air-contacted MoS2 powder. However higher band intensities and the use of labeled compound enabled us to identify the bands of coordinately bonded NH3 molecules and to point to the existence of acidic sites capable to protonate ammonia. Molecularly adsorbed CH3SH could be distinguished from its dissociative form; this reveals the existence of acid–base pair sites on bulk molybdenum sulfide.