Ammonia TPD Research Articles

Detailed Kinetic Modeling of NH3 and H2O Adsorption, and NH3 Oxidation over Cu-ZSM-5

The NH3 and H2O adsorption and desorption, and the NH3 oxidation was studied using detailed kinetic modeling and flow reactor experiments. Ammonia storage and ammonia oxidation are important for the NH3 SCR application. In this study, both ammonia storage and oxidation are investigated, with and without the presence of water. Four sites were included in the model. On each copper atom was one active site introduced, denoted S1a, where NH3, H2O, NO2 and O2 can adsorb. However, electron paramagnetic resonance studies (EPR) and also DFT calculations in the literature suggest that [Cu(NH3)4]2+complex are formed in copper zeolites. We therefore introduced three additional sites (S1b) that ammonia can adsorb on in order to add up to the four ammonia adsorbed per copper atom. It was important to separate between S1a and S1b since it is not possible for four NO2 to adsorb per copper and also in order to describe the ammonia TPD and SCR reactions simultaneously. The Cu-ZSM-5 catalyst also contains Bronsted acid sit...

Influence of the cobalt salt precursors on the cobalt speciation and catalytic properties of H-ZSM-5 modified with cobalt by solid-state ion exchange reaction

Abstract Co-ZSM-5 catalysts prepared by either aqueous or solid-state ion exchange using different cobalt precursors (acetate, chloride, nitrate or formate) were studied in the selective ammoxidation of ethylene and ethane to acetonitrile. Co 2+ supported catalysts were characterized by chemical analysis, X-ray powder diffraction, N 2 adsorption (BET), TEM/EDX, FTIR, XANES and EXAFS spectroscopy, H 2 TPR and TPD of ammonia. It was found that all the preparations led to cobalt exchanged metal ion at the bridging oxygen of Si–OH–Al groups or to Co oxide or phyllosilicate. XRD, TEM and H 2 TPR indicated the presence of cobalt oxide when cobalt chloride, formate or nitrate was used. TPD of ammonia and FTIR of pyridine, used respectively as probe molecules showed that solid-state exchange catalysts exhibited new Lewis acid sites. The catalyst resulting from cobalt acetate, which contained mostly isolated Co 2+ ions in cationic exchange position and cobalt phyllosilicate, showed high activity and selectivity toward acetonitrile.

Combined Method of Ammonia IRMS-TPD Experiment and DFT Calculation to Characterize Zeolite Acidity

Our recently developed potential characterization method for studying the zeolite acidity is reviewed. In this method, ammonia TPD is a principle technique and first the principle of the method was explained. In order to overcome the drawback existed in the usual TPD, IRMS-TPD method was developed, in which IR and MS were measured simultaneously to monitor the thermal behavior of ammonia molecules on the surface and in the gas phase. The developed method made it possible not only to measure the Bronsted and Lewis acid sites individually but also to clarify the distribution of Bronsted acid sites. In addition, DFT calculations were carried out to confirm the obtained information of the Bronsted acidity. Based on these studies, a new technique was developed by combining the IRMS-TPD experiment and DFT calculation to precisely characterize the zeolite acidity. Using the developed method, the modified Y zeolites active for the cracking of hydrocarbons were studied.

Continuous Hydroxyalkylation of p-Cresol to 2,2'-Methylenebis(4-Methylphenol) in a Fixed Bed Reactor

Catalytic activity of various solid acid catalysts is evaluated for the continuous hydroxyalkylation of p-cresol to [2,2′-methylenebis(4-methylphenol)] (DAM) in a fixed bed reactor. This is an industrially important process generally carried out in the presence of mineral acids. In the present study, we show that solid acids can be successfully used for this important process. The characterization of these solid acids is done using ammonia TPD measurement based on which the observed activity results can be explained. The performance of both batch and continuous operation has been studied for the hydroxyalkylation of p-cresol using the montmorillonite KSF/0 catalyst. The effect of reaction parameters such as mole ratio, temperature and catalyst concentration on the conversion of p-cresol and DAM selectivity have also been studied in both batch and fixed bed reactors. Significant difference is observed on the conversion of p-cresol and DAM selectivity with changing flow rate of reaction mixture in continuous operation.

Highly stable dealuminated zeolite support for the production of hydrogen by dry reforming of methane

Abstract Dealuminated FAU type Y and BEA zeolites were used as supports for the dry reforming of methane. Ni and Pt (1 or 0.5 wt%) were impregnated on these carriers to produce both monometallic and bimetallic catalysts. The catalysts were characterized before and after exposure to reaction conditions by XRD, X-ray fluorescence, N 2 adsorption, TGA, TPR, SEM, TEM and XPS analyses. The acidity of the fresh solids was also evaluated by TPD of ammonia and FT-IR measurements. The improvement of the accessibility with dealumination of the supports, as well as the high stability of the BEA zeolite support, generated high dispersion of the metals and improved catalytic activity of this solid. The FAU type Y supports show much more total acidity compared to that of BEA, which possess acid sites of medium strength. The results demonstrated that the bimetallic Ni–Pt/zeolite catalyst showed lower activity (e.g., NiPtY and NiPtβ activities were 1.70 and 1.90 g metal −1 h −1 , respectively) than that of the monometallic Pt/zeolite catalyst (e.g., PtY and Ptβ activities were close to 2.0 and 3.20 g metal −1 h −1 , respectively). NiY and Niβ were practically inactive, which could be attributed to the formation of deactivating whisker-like carbon deposits (approximately 60 wt%) on the metal particles, combined with the high acidity of the support, which was measured by FT-IR analysis. In the case of Pt dispersed on BEA zeolite, it produced lower carbon deposition (16 wt%) and this coke was easily removed by CO 2 . Dealuminated BEA zeolite appeared to be a promising candidate for dry reforming of methane application due to its high stability and selectivity during 24 h of time on stream, in comparison with alumina (activity = 0.90 mol g metal −1 h −1 ), active carbon (activity = 2.30 g metal −1 h −1 ), and other zeolites.

Selective hydroxyalkylation of phenol to bisphenol F over dodecatungstophosphoric acid (DTP) impregnated on fumed silica

The catalyst activity of various solid acids, such as fumed silica (SiO2), dodecatungstophosphoric acid (DTP), DTP impregnated on SiO2, amberlyst-15 and montmorillonite KSF/0, was studied for the hydroxyalkylation of phenol to bisphenol F. A well-dispersed DTP on SiO2 catalyst was prepared by the wet impregnation method. The effect of DTP loading on SiO2 was also compared with bulk DTP and other solid acid catalysts. 20% DTP/SiO2 catalyst gave the highest products yield of 34.2% and selectivity of 90.1% to bisphenol F, at 353 K and with a phenol-to-formaldehyde mole ratio of 5:1. Ammonia TPD studies of various catalysts showed that an appropriate combination of both strong and weak acid sites of DTP/SiO2 was mainly responsible, rather than only the stronger acidity of bulk DTP, for its highest catalytic activity and selectivity. The effect of various reaction parameters like mole ratio, catalyst concentration, temperature and reaction time on product yield and bisphenol F selectivity was also investigated. The catalyst recycle was established by catalyst activity testing.

Nano-ceria–zirconia promoter effects on enhanced coke combustion and oxidation of CO formed in regeneration of silica–alumina coked during cracking of triisopropylbenzene

Effects of Ce0.68Zr0.32O2 physically mixed with or impregnated on amorphous silica–alumina (SA) on enhanced combustion of coke and oxidation of CO formed in the regeneration of the catalysts coked during catalytic cracking of 1,3,5-triisopropylbenzene (TiPB) were studied. SA with about 535 m2/g BET surface area was synthesized using a co-precipitation method and ammonium exchanged. 6.0 wt% Ce0.68Zr0.32O2 on the silica–alumina was prepared by impregnation of the sample with an aqueous solution of cerium and zirconium nitrates and designated as Ce0.68Zr0.32O2/SA. Nanoparticles of Ce0.68Zr0.32O2, with around 12 nm crystallite size, were also prepared by a microwave induced combustion synthesis method and physically mixed with SA as another catalyst sample, i.e. Ce0.68Zr0.32O2·SA. The catalysts were characterized by SEM, EDS, XRD, BET, AAS, H2-TPR and ammonia TPD techniques. After in situ calcination at 475 °C for 3 h, the samples were coked by exposure to a gaseous stream of 5.0 vol% TiPB in Ar at 350 °C for 40 min. Temperature-programmed oxidation (TPO) method was employed to study the onset temperature of the coke combustion and CO oxidation during the regeneration of the coked catalyst in 2.0 vol% O2/N2 feed. At 3 min of cracking, TiPB cracking activities of both Ce0.68Zr0.32O2/SA and Ce0.68Zr0.32O2·SA samples are about the same and 5% lower than that of SA. The selectivity of cumene, as a deep cracking product, decreases in the order of SA > Ce0.68Zr0.32O2·SA > Ce0.68Zr0.32O2/SA concomitant with the density of acid sites of the catalysts. As compared to the SA, a decline of about 15.2% in coke formation is observed for the Ce0.68Zr0.32O2/SA sample. In addition, the Ce0.68Zr0.32O2 promotion of SA by physical mixing and impregnation lowers the CO evolution in the catalysts regeneration by about 51 and 61%, respectively. The highly active Ce0.68Zr0.32O2 oxygen is responsible for the higher conversion of CO to CO2 on the catalysts containing the promoter. Furthermore, the Ce0.68Zr0.32O2/SA sample, impregnated with Ce0.68Zr0.32O2 promoter, lowers the onset temperature of coke combustion by about 130 °C. This may be attributed to tight contact of the coke with active surface oxygen of the promoter.

Improvement of the catalytic isomerization performance for sulfated zirconias by use of templating techniques

Abstract New sulfated zirconias covering a wide range of pore diameters from micropores to macropores have been prepared by a combined use of two different structure-directing templates. The catalytic performance of these sulfated zirconias for the n -butane isomerization could be improved significantly compared to a standard displaying a maximum rate of isomerization of 1490 μmol/g h at 423 K. The materials remained their high activity even at 348 K. Moreover, deactivated materials could be reactivated to the original activity in an air-flow at 673 K several times. The newly designed materials were fully characterized by XRD, XPS, TPD of ammonia, IR spectroscopy and N 2 adsorption to describe the formation of active surface centres and their morphology. The formation of active pyrosulfates with sulfate bands above 1400 cm −1 was followed by DRIFTS. An increased ratio of Bronsted-to-Lewis centres could be detected which can be accounted for the unexpected high activity.

Synergetic effects of Y-zeolite and amorphous silica-alumina as main FCC catalyst components on triisopropylbenzene cracking and coke formation

The synergetic effects of HY-zeolite and silica-alumina (SA), as two major components of an FCC catalyst, on the cracking activity and coking tendency during catalytic cracking of 1,3,5-triisopropylbenzene (TiPB, as a resid representative) were studied. NaY-zeolite and SA were synthesized by hydrothermal and co-precipitation methods, respectively, and ammonium exchanged for three times at 80 °C. The catalysts were characterized by XRD, XRF, SEM, BET, AAS and ammonia TPD techniques. TiPB cracking was investigated on four different catalyst configurations including SA, Y-zeolite, SA.Y and SA-Y in a fixed bed reactor. SA.Y stands for physical mixture of equal amounts of Y-zeolite and SA. For SA-Y, a bed of SA was placed upstream of the same amount of Y-zeolite. The catalysts were in-situ activated at 475 °C and evaluated by TiPB cracking at 350 °C. The coke content of the catalyst beds, after 40 min cracking of TiPB, was estimated by TPO using an FT-IR gas cell. At 3 min time on stream, 5.2 times higher yield of benzene, as a deep cracking product, is observed on SA-Y as compared to SA.Y. The TiPB conversion decreases in the order of SA-Y > SA.Y > Y-zeolite ≫ SA. Furthermore, as compared to Y-zeolite, 24% lower coke is formed on SA-Y. Also CO evolution during TPO of coked SA-Y catalyst is about 24% lower than that of the coked zeolite. As a result, protecting of Y-zeolite by SA from direct exposure to resid feed enhances the cracking activity, decreases the tendency to coke formation and diminishes CO emission in the catalyst regeneration process.

Single-step synthesis of DME from syngas on Cu–ZnO–Al 2O 3/zeolite bifunctional catalysts: The superiority of ferrierite over the other zeolites

Single-step synthesis of DME was studied on four different bifunctional catalysts containing Cu–ZnO–Al 2O 3 as the common methanol synthesis component and ferrierite, ZSM-5, NaY or HY, as the solid acid component. The catalysts were prepared by co-precipitation of the metallic component in the slurry of the zeolite, and were characterized by nitrogen adsorption, XRD and ammonia TPD. Cu–ZnO–Al 2O 3/ferrierite is found to be superior to the other catalysts in terms of better conversion and DME selectivity because of facile reducibility of the metal component, suitable topology, proper acidic property and resistance towards catalyst deactivation.

Titanium-modified MCM-41 Prepared by Ultrasound and by Hydrothermal Treatment, Catalysts for Acetylation Reactions

Recibido el 3 octubre de 2007; aceptado el 12 marzo de 2008 Abstract. Mesoporous materials type Ti-MCM-41 prepared by hydrothermal and ultrasound-assisted techniques were characterized by XRD, SEM, TEM, nitrogen physisorption, ammonia TPD, UV- vis and FT-IR. Both showed the MCM-41 characteristic structure. Hydrothermal treatment allowed obtaining a well ordered mate- rial and ultrasound procedure gave a better titanium distribution. Electronic microscopy images revealed Ti dispersion zones as well as the quantity of metal in the structure. The catalytic activity of these materials were tested by acetylation of aromatic and steroidal alco- hols to afford the corresponding esters in good yields.

Montmorillonite for selective hydroxyalkylation of p-cresol

Performances of montmorillonite titanium silicate (TS-1) and dodecatungstophosphoric acid (DTP) were compared for the hydroxyalkylation of p-cresol into dihydroxydiarylmethane (DAM). Ammonia TPD studies of various catalysts showed that an appropriate combination of both strong and weak acid sites of montmorillonite was mainly responsible rather than only the stronger acidity of bulk DTP for its highest catalytic activity for selective hydroxyalkylation of p-cresol to DAM. The selectivity to DAM could be enhanced by adjusting reaction conditions like mole ratio of p-cresol to formaldehyde, reaction temperature, catalyst concentration, solvent and reaction time.

Dehydration of glycerol in gas phase using heteropolyacid catalysts as active compounds

Different silica-, alumina-, and aluminosilicate-supported heteropolyacid catalysts were prepared using phosphomolybdic acid H 3PMo 12O 40⋅ xH 2O, phosphotungstic acid H 3PW 12O 40⋅ xH 2O, silicotungstic acid H 4SiW 12O 40⋅ xH 2O, and ammonium phosphomolybdate (NH 4) 3PMo 12O 40⋅ xH 2O as precursor compounds. The as-synthesised solids were characterised by nitrogen adsorption, XRD, TG/DTA, Raman spectroscopy, and TPD of ammonia. Silica-supported heteropolyacids are rather well crystallised, whereas alumina-supported samples are X-ray amorphous. Investigations using Raman spectroscopy of calcined samples and TG/DTA revealed that molybdenum-containing heteropolyacids tend to decompose partly close to 400 °C into molybdates and MoO 3 whereas tungsten-containing samples are stable. This makes in particular tungsten-based materials interesting acid catalysts for the dehydration of glycerol in the gas phase. In particular, the influence of selected support materials, catalyst loading, and temperature on acrolein formation was studied at standardised reaction conditions (10% by weight of glycerol in water, 225–300 °C, modified contact time 0.15 kg h mol −1). Surprisingly, alumina is found to be superior to silica as support material with regard to catalyst activity and selectivity. Nevertheless, tungsten based heteropolyacids showed outstanding performance and stability. Acrolein was always the predominant product with maximum selectivity of 75% at complete conversion over silicotungstic acid supported over alumina and aluminosilicate.

Post-synthesis coating of alumina on the mesopore walls of SBA-15 by ammonia/water vapour induced internal hydrolysis and its consequences on pore structure and acidity

Post-synthesis alumina coating on the pore walls of SBA-15 mesoporous silica was accomplished by internally hydrolyzing preloaded alumina precursor using ammonia/water vapour as hydrolyzing agent at elevated temperature under autogenously generated pressure and subsequent calcination. The resulted alumina-coated materials were characterized by means of N 2 adsorption, XRD, TEM, FTIR, TPD of ammonia and pyridine adsorption. The N 2 adsorption and XRD results showed that during the coating procedure mesopore walls were restructured resulting in improvement in their uniformity which was diminished by high loading of alumina. The restructuring process was influenced by temperature and duration of NH 3/H 2O vapour treatment. The coated alumina layer was anchored on the pore walls via Si–O–Al linkages and thus both Bronsted and Lewis acid sites were generated after coating.

One-pot synthesis of superacid catalytic material SO 42−/ZrO 2–SiO 2 with thermostable well-ordered mesoporous structure

A superacid mesostructured catalyst was directly synthesized by adding sulfuric acid to mesoporous zirconia–silica synthesis mixtures, and was characterized by HRTEM, XRD, UV–Vis, nitrogen sorption, NH 3–TPD, and Pyridine–FTIR. The XRD patterns and electron diffraction micrographs of the calcined samples showed the ordered mesoporous structure and tetragonal crystalline in frameworks. The ammonia TPD, pyridine in situ FTIR, and paraffin isomerization illustrated a new acidic property of the samples. The synthesis of the mesoporous materials, which have stable crystalline frameworks, high surface area, and strong acidity, is very likely to have important technological implications for catalytic reactions of large molecules.

Activity and selectivity for hydroisomerisation of n-decane over Ni impregnated Pd/H-mordenite catalysts

Nickel impregnated Pd/H-mordenite catalysts with different Ni contents were synthesised and tested for hydroisomerisation of n-decane with flow H2 gas. The XRD analysis of the catalysts showed the decrease of intensity with increase in Ni addition. The average metal particle size, measured by TEM, is also increased by increasing the Ni loading up to 0.2 wt.%. The acidity of the catalysts measured by TPD of ammonia revealed the ion-exchange of the some acid sites by Ni2+. The oxidation states of Pd and Ni were identified by XPS. The reducibility of H-mordenite supported Pd, Ni and Ni-Pd catalysts was studied by TPR. The catalytic activities of Ni containing and Ni free Pd/H-mordenite catalysts were studied and found that addition of Ni up to 0.2 wt.% over 0.1 wt.% Pd/H-mordenite, increased the n-decane conversion and isomerisation selectivity. As the Ni content exceeded 0.2 wt.%, the conversion and cracked products are found to decrease and increase. Further Ni containing Pd/H-mordenite showed increased sustainability and favoured the protonated cyclopropane (PCP) intermediate mechanism in n-decane isomerisation. It has been concluded that Ni impregnated Pd/H-mordenite showed good activity towards n-decane isomerisation where isomerized products mixture showed better octane number.

The effect of aromatics on paraffin mild hydrocracking reactions (WNiPd/CeY–Al 2O 3)

The conversion of heavy paraffin and aromatics into a high-quality diesel fraction was performed in a microplant using a WNiPd/CeY-alumina catalyst. The effects of aromatics and naphtheno-aromatics on mild hydrocracking of hexadecane were studied at different concentrations. Two catalysts, with and without Pd and thermal treatment, were characterized by FTIR, XPS, and TPD of ammonia and ammonia plus naphthalene to complement previous study about the surface composition. The hydrocracking activity and selectivity were tested using different amounts and types of aromatics. This study demonstrated the presence of two acid strengths that contribute in different ways to paraffin and aromatics isomerization, ring opening, and cracking reactions. The product distribution obtained by mild hydrocracking of n-C 16 is between amorphous (SiO 2Al 2O 3) and Y-zeolite type of support. The aromatic adsorption on acid sites reduces the cracking rate and improves the survival of di- and tri-branched paraffin. A model for the path of reaction is discussed to explain the results.

Phosphotungstic acid on silica with modified acid sites as a solid catalyst for selective cleavage of tert-butyldimethylsilyl ethers

The strength and nature of acid sites of bulk phosphotungstic acid could be modified after dispersing it on silica support which was characterized by XRD, ammonia TPD and 31P MAS NMR techniques. This solid acid catalyst was found to be highly selective for the cleavage of tert-butyldimethylsilyl ethers at room temperature. The catalyst was easily recovered by filtration and could be reused for several times without loss of any activity giving a TON of 9.5 × 105.

Enhanced Sulfur Tolerance of Bimetallic PtPd/Al2O3 Catalysts for Hydrogenation of Tetralin by Addition of Fluorine

A series of mono- and bi-metallic Pt-Pd/Al2O3 samples with and without F were studied as aromatic hydrogenation catalysts. The effects of changing the order of impregnation of the Pt precursor and F as well as varying the calcination temperature (300–500 °C) were investigated. Temperature programmed reduction (TPR) results demonstrate the presence of a higher fraction of dispersed metal precursor species left on the surface from the impregnation (PtOxCly) on the Pt/Al2O3 sample calcined at high temperature. The impregnation of F before the Pt precursor significantly decreases the interaction between the metal and the support. However, this decrease is not observed when F is impregnated after the metal precursor. For the bimetallic Pt-Pd catalysts, the sample prepared adding F before the metal show a higher degree of Pt-Pd interaction than either the parent Pt-Pd/Al2O3 catalyst or the one prepared with F added later. TPD of ammonia result show the increase in strong acid sites when F is present. Activity tests for tetralin hydrogenation in the presence of 350 ppm dibenzothiophene indicate a better sulfur tolerance for all F-promoted catalysts, especially Pt-Pd.

Isomerization of 1-butene catalyzed by ion-exchanged, pillared and ion-exchanged/pillared clays

A natural smectite clay (STx-1, USA) was ion-exchanged with Al, Fe or pillared with polyoxocations of the same metals. Samples were also prepared by combining these two treatments. The prepared solids were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), thermogravimetric analysis (TGA), TPD of ammonia and N2 adsorption. The catalytic activity was evaluated by using the isomerization of 1-butene at 300 °C. XRF results showed an increase in the content of Al or Fe thus giving evidence that these metals were effectively exchanged or deposited over the starting material. Al- and Fe-pillared clays showed a significant increase of the surface area. Ion-exchanged clays showed similar surface areas to that of the starting clay. From XRD patterns only the Al-pillared clay gave an increase of the d-spacing. The synthesized pillared clays were superior catalysts for the isomerization of 1-butene than the ion-exchanged clays; the ion-exchanged/pillared clays showed a similar catalytic behavior as that of the parent pillared clays. The Al-pillared clay was the best catalyst for the reaction and its efficiency was related to the high acidity and high surface area.