Ru-CeOx/TiO2复合氧化物催化HCl氧化反应制Cl2

为提高钌基催化剂的高温稳定性,本文采用液相共浸法制备了一系列Ru-CeO _x /TiO₂复合氧化物催化剂,探究了CeO₂对钌基催化剂在HCl氧化过程中催化性能的影响。通过TEM、XRD、N₂吸附-脱附、Raman、XPS等表征手段分析催化剂结构及组成,结合催化剂在HCl催化氧化反应中的催化性能,研究了不同Ce负载量对RuO₂/TiO₂体系的作用规律。结果表明,引入Ce之后改变了活性相RuO₂与载体TiO₂的相互作用,形成了Ce-O-Ru结构,对钌基催化剂的活性产生一定的负面作用;但是由于抑制了Ru活性位点的烧结失活,同时高浓度的Ce³⁺物种有利于氧物种的吸附与活化,使含适量Ce的Ru-CeO _x /TiO₂复合氧化物催化剂能够在较高温度（370℃、400℃）下保持良好的高温稳定性与催化活性,最终确定摩尔比以Ru∶Ce=1∶1较为适宜。     

SO2 resistant antimony promoted V2O5/TiO2 catalyst for NH3-SCR of NOx at low temperatures

To get the low temperature sulfur resistant V₂O₅/TiO₂ catalysts quantum chemical calculation study was carried out. After selecting suitable promoters (Se, Sb, Cu, S, B, Bi, Pb and P), respective metal promoted V₂O₅/TiO₂ catalysts were prepared by impregnation method and characterized by X-ray diffraction (XRD) and Brunner Emmett Teller surface area (BET-SA). Se, Sb, Cu, S promoted V₂O₅/TiO₂ catalysts showed high catalytic activity for NH₃ selective catalytic reduction (NH₃-SCR) of NO_x carried at temperatures between 150 and 400 °C. The conversion efficiency followed in the order of Se > Sb > S > V₂O₅/TiO₂ > Cu but Se was excluded because of its high vapor pressure. An optimal 2 wt% ‘Sb’ loading was found over V₂O₅/TiO₂ for maximum NO_x conversion, which also showed high resistance to SO₂ in presence of water when compared to other metal promoters. In situ electrical conductivity measurement was carried out for Sb(2%)/V₂O₅/TiO₂ and compared with commercial W(10%)V₂O₅/TiO₂ catalyst. High electrical conductivity difference (ΔG) for Sb(2%)/V₂O₅/TiO₂ catalyst with temperature was observed. SO₂ deactivation experiments were carried out for Sb(2%)/V₂O₅/TiO₂ and W(10%)/V₂O₅/TiO₂ at a temperature of 230 °C for 90 h, resulted Sb(2%)/V₂O₅/TiO₂ was efficient catalyst. BET-SA, X-ray photoelectron spectroscopy (XPS) and carbon, hydrogen, nitrogen and sulfur (CHNS) elemental analysis of spent catalysts well proved the presence of high ammonium sulfate salts over W(10%)/V₂O₅/TiO₂ than Sb(2%)/V₂O₅/TiO₂ catalyst.     

Support effects in Pt/TiO2–ZrO2 catalysts for NO reduction with CH4

ZrO₂–TiO₂ mixed oxides, prepared using the sol–gel method, were used as supports for platinum catalysts. The effects of catalyst pre-reduction and surface acidity on the performance of Pt/ZT catalysts for the reduction of NO with CH₄ were studied. The diffuse reflectance infrared Fourier transformed (DRIFT) spectra of CO adsorbed on the Pt/ZT catalysts, and also on the Pt/T and Pt/Z references, pre-reduced at 773 K in hydrogen, revealed that an SMSI state is developed in the Ti-rich oxide-supported platinum catalysts. However, no shift in the binding energy of Pt 4f_7/2 level for Pt/T and Pt deposited on Ti-rich support counterparts pre-reduced at 773 K was found by photoelectron spectroscopy. The DRIFT spectra of the catalysts under the NO+O₂ co-adsorption revealed the appearance of nitrite/nitrate species on the surface of the Zr-containing catalysts, which displayed acidic properties, but were almost absent in the Pt/T catalyst. The intensity of these bands reached a maximum for the Pt/ZT(1:1) catalyst, which in turn exhibited a larger specific area. In the absence of oxygen in the feed stream, the NO+CH₄ reaction showed DRIFT spectra assigned to surface isocyano species. Since the intensity of this band is higher for the Pt/ZT (9:1) catalyst, it seems that such species are developed at the Pt–support interface.     

Ni/Al_2O_3催化剂的CO_2-TPD表征

Ni/Al_2O_3催化剂是甲烷二氧化碳重整反应制取合成气研究最多、最具应用潜力的一种催化剂。通过对催化剂进行CO_2-TPD研究,考察还原态Ni/Al_2O_3催化剂的CO_2脱附特性。结果表明,浸渍法制备的Ni/Al_2O_3催化剂CO_2脱附曲线呈现双峰,分别在(60~65)℃和(350~380)℃出现高低温两个活性位;高温CO_2吸附量为3.0 cm~3·g~(-1),低温CO_2吸附量为24.0 cm~3·g~(-1)。催化剂的CO_2吸附量与其Ni含量无关。考察选用不同载体的CO_2脱附行为,发现以Al_2O_3为载体的催化剂CO_2吸附量是MgO和SiO_2为载体催化剂的2~4倍,以TiO_2为载体的催化剂几乎不吸附CO_2。     

Characterization and photocatalytic activity of transition-metal-supported surface bond-conjugated TiO2/SiO2

TM/TiO₂/SiO₂ photocatalysts were prepared by the photodeposition method using transition metal salts (TM=Fe³⁺, Co²⁺, Ni²⁺ and Cu²⁺) as precursors and the surface bond-conjugated TiO₂/SiO₂ as supporter in N₂ atmosphere, and were characterized by XRD, XPS, UV-Vis diffuse reflection and zeta-potential. Their photocatalytic activities were evaluated using reactive brilliant red K-2G (K-2G) and cationic blue X-GRL (CBX) showing different adsorption behavior on the oxides. Fe, Cu supported TiO₂/SiO₂ can efficiently extend the light absorption to the visible region. XPS analysis verified that the introduction of transition metal lead to the changes of the electronic environmental of Ti cations and the zeta-potential of oxides. As a result, K-2G has higher adsorption on the modified TiO₂/SiO₂ than that on the baked one, while the adsorption of CBX has a little change on the both oxides. At the same time, for the photodegradation of K-2G, Fe³⁺, Co²⁺, Ni²⁺-modified catalysts show that their photoactivities are 3.3–2.2 times higher than the bare one. On the contrast, all transition-metal-supported catalysts have no significant activity improvement except that Fe/TiO₂/SiO₂ shows 1.68 times higher activity for the photodegradation of CBX. The results indicate that the photoactivity could be increased in photodegradation of dyes by changing the performances of adsorption to dyes and absorption to light of photocatalyst.     

TiO2-SiO2 and V2O5/TiO2-SiO2 catalyst: Physico-chemical characteristics and catalytic behavior in selective catalytic reduction of NO by NH3

TiO₂-SiO₂ with various compositions prepared by the coprecipitation method and vanadia loaded on TiO₂-SiO₂ were investigated with respect to their physico-chemical characteristics and catalytic behavior in SCR of NO by NH₃ and in the undesired oxidation of SO₂ to SO₃, using BET, XRD, XPS, NH₃-TPD, acidity measurement by the titration method and activity test. TiO₂-SiO₂, compared with pure TiO₂, exhibits a remarkably stronger acidity, a higher BET surface area, a lower crystallinity of anatase titania and results in allowing a good thermal stability and a higher vanadia dispersion on the support up to high loadings of 15 wt% V₂O₅. The SCR activity and N₂ selectivity are found to be more excellent over vanadia loaded on TiO₂-SiO₂ with 10–20 mol% of SiO₂ than over that on pure TiO₂, and this is considered to be associated with highly dispersed vanadia on the supports and large amounts of NH₃ adsorbed on the catalysts. With increasing SiO₂ content, the remarkable activity decrease in the oxidation of SO₂ to SO₃, favorable for industrial SCR catalysts, was also observed, strongly depending on the existence of vanadium species of the oxidation state close to V⁴⁺ on TiO₂-SiO₂, while V⁵⁺ exists on TiO₂, according to XPS. It is concluded that vanadia loaded on Ti-rich TiO₂-SiO₂ with low SiO₂ content is suitable as SCR catalysts for sulfur-containing exhaust gases due to showing not only the excellent de-NO_x activity but also the low SO₂ oxidation performance.     

Improvement of catalytic activity and sulfur-resistance of Ag/TiO2–Al2O3 for NO reduction with propene under lean burn conditions

Ag-based catalysts supported on various metal oxides, Al₂O₃, TiO₂, and TiO₂–Al₂O₃, were prepared by the sol–gel method. The effect of SO₂ on catalytic activity was investigated for NO reduction with propene under lean burn condition. The results showed the catalytic activities were greatly enhanced on Ag/TiO₂–Al₂O₃ in comparison to Ag/Al₂O₃ and Ag/TiO₂, especially in the low temperature region. Application of different characterization techniques revealed that the activity enhancement was correlated with the properties of the support material. Silver was highly dispersed over the amorphous system of TiO₂–Al₂O₃. NO₃⁻ rather than NO₂⁻ or NOx reacted with the carboxylate species to form CN or NCO. NO₂ was the predominant desorption species in the temperature programmed desorption (TPD) of NO on Ag/TiO₂–Al₂O₃. More amount of formate (HCOO⁻) and CN were generated on the Ag/TiO₂–Al₂O₃ catalyst than the Ag/Al₂O₃ catalyst, due to an increased number of Lewis acid sites. Sulfate species, resulted from SO₂ oxidation, played dual roles on catalytic activity. On aged samples, the slow decomposition of accumulated sulfate species on catalyst surface led to poor NO conversion due to the blockage of these species on active sites. On the other hand, catalytic activity was greatly enhanced in the low temperature region because of the enhanced intensity of Lewis acid site caused by the adsorbed sulfate species. The rate of sulfate accumulation on the Ag/TiO₂–Al₂O₃ system was relatively slow. As a consequence, the system showed superior capability for selective adsorption of NO and SO₂ toleration to the Ag/Al₂O₃ catalyst.     

Performance and characterization of Ru/Al2O3 and Ru/SiO2 catalysts modified with Mn for Fischer–Tropsch synthesis

Mn effect and characterization on γ-Al₂O₃-, -Al₂O₃- and SiO₂-supported Ru catalysts were investigated for Fischer–Tropsch synthesis under pressurized conditions. In the slurry phase Fischer–Tropsch reaction, γ-Al₂O₃ catalysts showed higher performance on CO conversion and C₅⁺ selectivity than -Al₂O₃ and SiO₂ catalysts. Moreover, Ru/Mn/γ-Al₂O₃ exhibited high resistance to catalyst deactivation and other catalysts were deactivated during the reaction. From characterization results on XRD, TPR, TEM, XPS and pore distribution, Ru particles were clearly observed over the catalysts, and γ-Al₂O₃ catalysts showed a moderate pore and particle size such as 8 nm, where -Al₂O₃ and SiO₂ showed highly dispersed ruthenium particles. The addition of Mn to γ-Al₂O₃ enhanced the removal of chloride from RuCl₃, which can lead to the formation of metallic Ru with moderate particle size, which would be an active site for Fischer–Tropsch reaction. Concomitantly, manganese chloride is formed. These schemes can be assigned to the stable nature of Ru/Mn/γ-Al₂O₃ catalyst.     

The role of oxygen vacancies during the decomposition of RhCl3/TiO2 precursor: study by XPS, IR, EPR and NMR.

Thermal reduction under ultrahigh vacuum or with H₂ of RhCl₃/TiO₂ precursors up to 773K has been studied either directly or after precalcination with O₂ at 773K. The evolution of rhodium and chlorine has been followed with the aid of XPS, EPR, IR ¹H-NMR and TPR/DTG for the different treatments. Ar⁺ sputtering has been used in combination with XPS to examine in detail the incorporation of chlorine to the TiO₂ support. A model is proposed which assumes the formation during the reduction process of oxygen vacancies (Vo) associated to Ti³⁺ species (i.e. (TiVo)_n³ⁿ⁺). These centers act promoting the reduction of Rh³⁺ to Rh^o and upon extensive reduction at 773K in H₂, as anchoring sites of Rh^o through interaction with exposed Ti³⁺ ions. Oxygen vacancies sites are also able to incorporate chlorine and hydrogen to form in the later case hydride, (Ti-H)³⁺, species that we have previously found to have a role in the SMSI state.     

Development of an in-situ H2 reduction and moderate oxidation method for 3,5-dimethylpyridine hydrogenation in trickle bed reactor

The Ru/C catalyst prepared by impregnation method was used for hydrogenation of 3,5-dimethylpyridine in a trickle bed reactor. Under the same reduction conditions (300 °C in H₂), the catalytic activity of the non-in-situ reduced Ru/C-n catalyst was higher than that of the in-situ reduced Ru/C-y catalyst. Therefore, an in-situ H₂ reduction and moderate oxidation method was developed to increase the catalyst activity. Moreover, the influence of oxidation temperature on the developed method was investigated. The catalysts were characterized by Brunauer–Emmett–Teller method, hydrogen temperature programmed reduction H₂-TPR, hydrogen temperature-programmed dispersion (H₂-TPD), X-ray diffraction, energy dispersive spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, O₂ chemisorption and oxygen temperature-programmed dispersion (O₂-TPD) analyses. The results showed that there existed an optimal Ru/RuO_x ratio for the catalyst, and the highest 3,5-dimethylpyridine conversion was obtained for the Ru/C-i1 catalyst prepared by in-situ H₂ reduction and moderate oxidation (oxidized at 100 °C). Excessive oxidation (200 °C) resulted in a significant decrease in the Ru/RuO_x ratio of the in-situ H₂ reduction and moderate oxidized Ru/C-i2 catalyst, the interaction between RuO_x species and the support changed, and the hard-to-reduce RuO_x species was formed, leading to a significant decrease in catalyst activity. The developed in-situ H₂ reduction and moderate oxidation method eliminated the step of the non-in-situ reduction of catalyst outside the trickle bed reactor.     

The CO–H2 and CO–H2O reactions over TiO2 nanotubes filled with Pt metal nanoparticles

We have investigated the catalytic behavior of Pt encapsulated TiO₂ nanotubes for the water gas shift reaction as well as the hydrogenation of CO. Pt–TiO₂ nanotube catalysts were prepared by employing fine fiber shaped crystals of [Pt(NH₃)₄](HCO₃)₂ complex as a structure determining template material. The turnover frequencies (TOF) of these nanotube catalysts were more than one order of magnitude larger than conventional impregnation Pt/TiO₂ catalysts, and the selectivity for methanol in CO–H₂ reaction was extraordinary high compared to the impregnation catalysts. The XPS and XRD analyses of the nanotubes revealed characteristic electronic state of reduced TiO₂ (Ti³⁺ in rutile structure) with zerovalent Pt even after the calcination at 773 K. In WGS reaction, electron rich Ti³⁺ on the nanotube wall may play an important role to activate water molecules for the oxidation of CO. In CO–H₂ reaction, similar promotion effect of Ti³⁺ species may be operating for selective methanol formation by supplying active OH(a).     

Production of hydrogen via partial oxidation of methanol over Au/TiO2 catalysts

Selective production of hydrogen by partial oxidation of methanol (CH₃OH + (1/2)O₂ → 2H₂ + CO₂) over Au/TiO₂ catalysts, prepared by a deposition–precipitation method, was studied. The catalysts were characterized by XRD, TEM, and XPS analyses. TEM observations show that the Au/TiO₂ catalysts exhibit hemispherical gold particles, which are strongly attached to the metal oxide support at their flat planes. The size of the gold particles decreases from 3.5 to 1.9 nm during preparation of the catalysts with the rise in pH from 6 to 9 and increases from 2.9 to 4.3 nm with the rise in calcination temperature up to 673 K. XPS analyses demonstrate that in uncalcined catalysts gold existed in three different states: i.e., metallic gold (Au⁰), non-metallic gold (Au^δ+) and Au₂O₃, and in catalysts calcined at 573 K only in metallic state. The catalytic activity is strongly dependent on the gold particle size. The catalyst precipitated at pH 8 and uncalcined catalysts show the highest activity for hydrogen generation. The partial pressure of oxygen plays an important role in determining the product distribution. There is no carbon monoxide detected when the O₂/CH₃OH molar ratio in the feed is 0.3. Both hydrogen selectivity and methanol conversion increase with increasing the reaction temperature. The reaction pathway is suggested to consist of consecutive methanol combustion, partial oxidation and steam reforming.     

A practical scale evaluation of sulfated V2O5/TiO2 catalyst from metatitanic acid for selective catalytic reduction of NO by NH3

The characteristics of sulfated V₂O₅/TiO₂ honeycomb catalyst from metatitanic acid (MTA) were studied in the practical conditions of pilot plant using high dust flue gas from coal fired utility boiler. The effects of reaction temperature, NH₃/NO mole ratio, space velocity and operation time on the reduction of nitric oxide (NO) were mainly investigated for engineering application. The catalyst showed high NO reduction of about 90% at a space velocity of 4000 h⁻¹, NH₃/NO mole ratio of 1.0 and reaction temperature of 300–400 °C. The efficiency of this catalyst remained constant during the present experiment of 2400 h and the erosion by fly ash was lower than that of the commercial catalysts. These results clearly demonstrate the high potential for this catalyst to be applied commercially for the control of NO_x emissions from coal fired utility boiler.     

Partial oxidation of methane to CO and H2 over nickel and/or cobalt containing ZrO2, ThO2, UO2, TiO2 and SiO2 catalysts

The influence of different metal oxide supports (i.e. ZrO₂, ThO₂, UO₂, TiO₂ and SiO₂) on the performance of Ni- and/or Co-containing catalysts [Ni and/or Co/MO₂ mole ratio (where M=Zr, Th, U, Ti or Si)=1.0] in the oxidative methane-to-syngas conversion at very low contact time (GHSV=5.2×10⁵ cm³ g⁻¹ h⁻¹ at STP) was investigated. The nickel-containing ZrO₂, ThO₂ and UO₂ catalysts (with or without pre-reduction by hydrogen at 500°C) showed good performance in the process; the order of their performance is NiO–ThO₂>NiO–UO₂>NiO–ZrO₂. The NiO–TiO₂ showed appreciable catalytic activity only after its reduction at 800°C. However, this catalyst and the NiO–SiO₂ catalyst showed poor performance in the process. These two catalysts are also deactivated very fast, mostly because of sintering of Ni and/or formation of catalytically inactive binary metal oxide phases by solid–solid reaction at the high catalyst calcination and/or catalytic reaction temperature. Although the Ni-containing ThO₂, UO₂ and ZrO₂ catalysts showed good performance, carbon deposition on them during the process is fast. However, because of the addition of cobalt to these catalysts (with Co/Ni=1.0), the rate of carbon deposition on them in the process is drastically reduced. This Co addition however resulted in a significant decrease in both the conversion and selectivity; the decrease in the selectivity was small.     

Conversion of N2O to N2 on TiO2(1 1 0)

In this study, we examine the interaction of N₂O with TiO₂(1 1 0) in an effort to better understand the conversion of NO_x species to N₂ over TiO₂-based catalysts. The TiO₂(1 1 0) surface was chosen as a model system because this material is commonly used as a support and because oxygen vacancies on this surface are perhaps the best available models for the role of electronic defects in catalysis. Annealing TiO₂(1 1 0) in vacuum at high temperature (above about 800 K) generates oxygen vacancy sites that are associated with reduced surface cations (Ti³⁺ sites) and that are easily quantified using temperature programmed desorption (TPD) of water. Using TPD, X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS), we found that the majority of N₂O molecules adsorbed at 90 K on TiO₂(1 1 0) are weakly held and desorb from the surface at 130 K. However, a small fraction of the N₂O molecules exposed to TiO₂(1 1 0) at 90 K decompose to N₂ via one of two channels, both of which are vacancy-mediated. One channel occurs at 90 K, and results in N₂ ejection from the surface and vacancy oxidation. We propose that this channel involves N₂O molecules bound at vacancies with the O-end of the molecule in the vacancy. The second channel results from an adsorbed state of N₂O that decomposes at 170 K to liberate N₂ in the gas phase and deposit oxygen adatoms at non-defect Ti⁴⁺ sites. The presence of these O adatoms is clearly evident in subsequent water TPD measurements. We propose that this channel involves N₂O molecules that are bound at vacancies with the N-end of the molecule in the vacancy, which permits the O-end of the molecule to interact with an adjacent Ti⁴⁺ site. The partitioning between these two channels is roughly 1:1 for adsorption at 90 K, but neither is observed to occur for moderate N₂O exposures at temperatures above 200 K. EELS data indicate that vacancies readily transfer charge to N₂O at 90 K, and this charge transfer facilitates N₂O decomposition. Based on these results, it appears that the decomposition of N₂O to N₂ requires trapping of the molecule at vacancies and that the lifetime of the N₂O–vacancy interaction may be key to the conversion of N₂O to N₂.     

On the mechanism of model diesel soot-O2 reaction catalysed by Pt-containing La-doped CeO2: A TAP study with isotopic O2

Pt supported on CeO₂ and 10 wt.% La³⁺-doped CeO₂ catalysts have been prepared, characterised and tested for soot oxidation by O₂ in TGA. The reaction mechanism has been studied in a TAP reactor with labelled O₂. Isotopic oxygen exchange between molecular O₂ and ‘O’ on the support/catalyst was observed and soot oxidation is being carried out by lattice oxygen. TAP studies further show that Pt improves O₂ adsorption and, therefore, 5 wt.% Pt-containing catalysts are more active for soot oxidation than the counterpart supports. In addition, CeO₂ doping by La³⁺ leads to an improved support, since La³⁺ stabilises the structure of CeO₂ when calcined at high temperature (1000 °C) and minimises sintering. In addition, La³⁺ improves the Ce⁴⁺/Ce³⁺ reduction as deduced from H₂-TPR experiments and favours oxygen mobility into the lattice. A synergetic effect of Pt and La³⁺ is observed, Pt-containing La³⁺-doped CeO₂ being the most active catalyst for soot oxidation by O₂ among the samples studied.     

Reactivity of V2O5-WO3/TiO2 catalysts in the selective catalytic reduction of nitric oxide by ammonia

The physico-chemical characteristics and the reactivity of sub-monolayer V₂O₅-WO₃/TiO₂ deNO_x catalysts is investigated in this work by EPR, FT-IR and reactivity tests under transient conditions. EPR indicates that tetravalent vanadium ions both in magnetically isolated form and in clustered, magnetically interacting form are present over the TiO₂ surface. The presence of tungsten oxide stabilizes the surface V^IV and modifies the redox properties of V₂O₅/TiO₂ samples. Ammonia adsorbs on the catalysts surface in the form of molecularly coordinated species and of ammonium ions. Upon heating, activation of ammonia via an amide species is apparent. V₂O₅-WO₃/TiO₂ catalysts exhibits higher activity than the binary V₂O₅/TiO₂ and WO₃/TiO₂ reference sample. This is related to both higher redox properties and higher surface acidity of the ternary catalysts. Results suggest that the catalyst redox properties control the reactivity of the samples at low temperatures whereas the surface acidity plays an important role in the adsorption and activation of ammonia at high temperatures.     

CO_2 methanation over TiO_2–Al_2O_3 binary oxides supported Ru catalysts

TiO_2 modified Al_2O_3 binary oxide was prepared by a wet-impregnation method and used as the support for ruthenium catalyst. The catalytic performance of Ru/TiO_2–Al_2O_3catalyst in CO_2 methanation reaction was investigated. Compared with Ru/Al_2O_3 catalyst, the Ru/TiO_2–Al_2O_3catalytic system exhibited a much higher activity in CO_2 methanation reaction. The reaction rate over Ru/TiO_2–Al_2O_3 was 0.59 mol CO_2·(g Ru)1·h-1, 3.1 times higher than that on Ru/Al_2O_3[0.19 mol CO_2·(gRu)-1·h-1]. The effect of TiO_2 content and TiO_2–Al_2O_3calcination temperature on catalytic performance was addressed. The corresponding structures of each catalyst were characterized by means of H_2-TPR, XRD, and TEM. Results indicated that the averaged particle size of the Ru on TiO_2–Al_2O_3support is 2.8 nm, smaller than that on Al_2O_3 support of 4.3 nm. Therefore, we conclude that the improved activity over Ru/TiO_2–Al_2O_3catalyst is originated from the smaller particle size of ruthenium resulting from a strong interaction between Ru and the rutile-TiO_2 support, which hindered the aggregation of Ru nanoparticles.     

Selective catalytic reduction of N2O in industrial emissions containing O2, H2O and SO2: behavior of Fe/ZSM-5 catalysts

The catalytic behavior in N₂O reduction by propane in the presence of O₂, H₂O and SO₂ of Fe/ZSM-5 catalysts prepared by ion exchange and chemical vapour deposition (CVD) is reported. The catalyst prepared by CVD shows a lower dependence of the rate of selective N₂O reduction on the decrease in C₃H₈ to N₂O ratio in the feed and a higher resistance to deactivation by SO₂ in accelerated durability tests with high SO₂ concentration (500 ppm). This catalyst shows stable catalytic behavior in the presence of SO₂ for more than 600 h of time-on-stream. Characterization of the catalysts by UV–VIS–NIR diffuse reflectance indicates that the poor performances of the sample prepared by ion exchange could be related to the presence of highly clustered Fe³⁺ species, in this catalyst. On the other hand, Fe₂O₃ particles are not present in the sample prepared by CVD while mainly isolated Fe³⁺ ions and iron-oxide nanoclusters are present.     

Bound-state Ni species — a superior form in Ni-based catalyst for CH4/CO2 reforming

The effects of nickel loading, calcination temperature, support, and basic additives on Ni-based catalyst structure and reactivity for CH₄ reforming with CO₂ were investigated. The results show that the structure of the nickel active phase strongly depends on the interactions of the metal and the support, which are related to the support properties, the additives and the preparation conditions. “Free” Ni species can be formed when the interaction is weak and their mobility makes them easily deactivated by coking and sintering. The effect of strong metal-support interaction (SMSI effect) is different for various supports. The formation of solid solution of Ni–Mg–O₂ and the blocking of TiO_x by the partially reduced TiO₂ can both decrease the availability of Ni active sites in Ni/MgO and Ni/TiO₂. The spinel NiAl₂O₄ formed in Ni/γ-Al₂O₃ might be responsible for its high activity and resistance to coking and sintering because it can produce a highly dispersed active phase and a large active surface area as bound-state Ni species when the catalyst is prepared at high calcined temperatures or with low nickel loading. The addition of La₂O₃ or MgO as alumina modifiers can also be beneficial for the performance of the Ni/γ-Al₂O₃ catalyst.