XRD applications in relevant papers

Merve AyvazBoazii UniversityXRD Applications in Relevant Papers

Combined XRD and XANES studies of Re-promoted Co/-Al2O3 catalyst at Fischer-Tropsch synthesis conditions,Ronning at al.,2010, Catalyst Today 155Detecting changes in Co oxidation state and crystallite size during the initial stages of the FT reactions at industrail conditions.Resutl of XRD:Co dispersion depends on technique and it is 6-9%Particle size:11-16 nm

Reduction of Co and Crystallite SizeReduction of Co

Most intense peaks are observed 16.54 for Co3O418.93 for CoO20.44 for CoNo Rhenium phase is not detected- so, highly dispersed.

Co3O4 (spinel structure of the freshly calcined catalyst)CoO metastable phaseCo0 (fcc and hcp)Heating rate and composition of the reducing gas mixture influence the crystallite size distribution.Phase transition is monitored by XRD with sufficient time resolution. =0.70417 A

Hcp : hexagonal close packing3

Apply the Scherrer equation to maximum intense peaks. (minimize overlapping peaks at max. intensity)

Metallic cobalt crystallite size reduced 40% comparing to initial state.It is expected to decrease due to loss of oxygen.

X-Ray Line Boarding Analysis-Crystallite Size

Crystallite SizeCo3O4 and CoO phases contain significant amount of strain. (WilliamsonHall plots)The diffraction peaks is not purely due to finite crystallites.Stacking faults in the metallic cobalt phases may have contributed to the broadening of the diffraction peaks. The existence of other sample dependent broadening effects implies that the crystallite sizes calculated from the Scherrer equation will be underestimated.

XANES Data- X-ray Absorption Near Edge Structure (XANES)DOR= the fraction of Co in the metallic stateThe same sample after reduction show a degree of reduction (DOR) in the range of 90%.

CoO in the metallic cobalt particles may reduce the calculated Scherrer size of the cobalt crystallitesRedispersion of cobalt crystallites during reduction can not be excluded.In contrast, all the Co3O4 is transformed.The relatively small size of the CoO crystallites cannot be explained solely by the existence of larger domains of Co3+ -containing oxide inside the CoO particles.

d(Cocpp)=0.80d(Co3O4)

X-ray Absorption Near Edge Structure (XANES)XANES data indicate the absorption peaks due to the photoabsorptioncross sectionin the X-ray Absorption Spectra6

XRD During FT Synthesis

FTS carried out 463K at 10 bar 2 hour.-Initial ReactionReaction is monitored by on-line quadrople mass spectrometer (MS) and XRD.TOS= Ions currents during time on stream

No visible changes are detected in the diffraction peaks

Examination of the Diffractograms Before and After Initial ReactionThe metallic cobalt peaks remain unchanged during this initial stage of the reaction. Crystallite sizes before and at the end of the reaction were both 10.7 nm.Change of wax peak may depend on variation in product distribution and steam partial pressure from the present reaction conditions.

9.35oWax-LHC

Once 473 te 2 saat reaksyona sokuluyor, daha sonra 673, bu sintering olusumunu engellemek iin boyle yaplr.8

FTS @ 673K, 10K/min, 10 bar, 1 hourFTS was subsequintly carried out at 673 K.Increase in the Scherrer size of the cobalt crystallites about 20% after 1 hour.Particle growth seems to start immediately after the applied conditions are reached.

Liquid products were detected as an increase in the scattering intensity at lower XRD angles. Liquid products gradually fill the catalyst pores and the reactor during the initial stages of the reaction.No detectable changes in the cobalt crystallite size during the reaction. (XRD line broadening analysis showed)

FTS @ 483 K, 18 bar, 6 hours (industrially relevant conditions)

(a) The difference curve (green) of the two diffractograms collected at thestart (black) and at the end of the experiment FT3 (red)

. The sharp narrow peakscorrespond to BN. (b) LBA at different stages of the reaction using the Scherrerequation, l = 0.8007A . (For interpretation of the references to colour in this figurelegend, the reader is referred to the web version of the article.)10

Oxidation State of Cobalt by XANESXANES spectra were recorded during reduction.According to spectra cobalt in the catalyst sample before reduction is present as Co3O4. During reduction it is first transformed to CoO and further to metallic cobalt. Cobalt oxide is not completely reduced to cobalt metal. 10% of the cobalt remains in the non-metallic phase after reduction for 4 h at 673 K in H2.

Co3O4CoOCoTThe catalyst maintained a degree of reduction close to 90%.

Oxidation of Co During the FTS by XANES

No significant change in oxidation state of cobalt during 6 hour.

Oxidation of Cobalt during FTS (industrail) by XANES

Oxidation of Co during FTS (673 K,10 bar), by XRDDecrease in the intensity of CoO peaks, further reduction of Co.Co crystallite size increase slightly.

ConclusionA 20%Co-1%Re/g-Al2O3 catalyst characterised by XRD and XANES methods at realistic FischerTropsch conditions (483 K, 10 and 18 bar) in a plug flow reactor. Conversion was monitored using an on-line MS.XRD and XANES are sensitive to structural changes such as crystallite size and oxidation state, respectively. At 673 K further reduction of cobalt were observed.

Characterization of K2CO3/Co-MoS2 catalyst by XRD,SEM and EDSIranmahboob at al.,2001, Applied Surface Sciences 185Utilization of XRD and XPS to characterize MoS2,Co-MoS2 and K2CO3/Co-MoS2 catalyst.Investigation of K2CO3/Co-MoS2 catalyst as a function of dispersion of K on the surface by SEM and EDS.

Energy-dispersive X-ray spectroscopy EDSMolybdenumMo

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XRD Pattern of MoS2Pattern is compared with literature The absence of some XRD peaks confirm the amorphous character of MoS3.Rapid increase of temperature during reduction, increase the surface area and presence of amorphous particles.

33.50d=2.6739.50d=2.28500d=1.82590d=1.56

XRD Pattern of Co-MoS2Diffraction lines of MoS2 are not change upon addition of Co. (Co/Mo=0.5) However, new lines are were observed. With addition of Co no side product Co9S8 was produced. No peak at 29.9o and 51.9o.

32.70d=2.7436.50d=2.4645.50d=1.9555.50d=1.65600d=1.54

XRD Pattern of K2CO3/ Co-MoS2The diffraction lines of Co-MoS2 did not changed.Upon addition of K2CO3 new lines are observed.Co-MoS2 is the primary phase in the catalyst.

26.50d=3.36320d=2.7937.50d=2.6753.50d=1.71

XPS, comparison between MoS2/Co-MoS2 and K2CO3/Co-MoS2 O 1s peak of MoS2 shifted by about 1 eV to higher BE for Co-MoS2Oxygen was present on Co and MoS2; may be due to the air exposure or incomplete calcinations. When potassium carbonate was added to the system Mo and Co are shifted to the lower energies.

X-rayphotoelectron spectroscopy (XPS)19

SEM and EDS for K2CO3/Co-MoS2 CatalystPotassium distribution is not uniform on the surface. (SEM)K and Mo+S (Mo and S observed in the same BE) peaks are different.If K2CO3 and Co-MoS2 was ground together and exposed to syngas for 6 hours, catalyst achieved an uniform distribution of K.

ConclusionCo-MoS2 is the primary phase in K2CO3/Co-MoS2 .Co9S8 phase is not present at Co/Mo mole ratio of 0.5. XPS binding energy difference of molybdenum sulfide (67.2 eV) is not changed for the MoS2, Co-MoS2, and K2CO3/Co-MoS2 catalyst. The distribution of the potassium on the surface of K2CO3/Co-MoS2 catalyst in not uniform when a physical mixing method is used to prepare catalyst.

An XRD and ESR study of V2O5/ZrO2 catalysts: influence of the phase transitions of ZrO2 on the migration of V4+ ions in to zirconiaAdamski at al.,1998, Solid State Ionics 117

Determination of the catalytic properties of potassium doped zirconia-supported V2O5 catalyst.

Phase Composition of ZrO2 matrixPolymorphic forms are temperature dependant.

Literature1V/ZrK-3V/Zr

Calcination of 1V/Zr MatrixIt is calcined at 853 K, consist of 2 phases: metastable tetragonal and monoclinic.

Upon increasing the calcination temperature to 1253 K. Tetragonal phase disapperingCrystallite size increases

K-3V/Zr calcined at 853 K. But the ratio of the peak intensities (111)M/(111)T are differentSo the phase composition depend on both temperature and chemical composition(additives)

(111)M/(111)T Intensity Ratios

Beginning of phase transition975 K1025 KStrong interactions between vanadia and the supported material stabilize tetragonal zincoria in the absence of alkali additives up to 1025K

850 ye kadar 3 iinde constant.K-po25

Temperature induce migration of V4+ ions into zirconiaVanadia (V5+ ) partially dissociates and loses some oxygen depending on the calcinations temperature.Leads to the formation of vanadium in lower oxidation states.V4+ ions can directly substitute Zr4+ ions in the cationic sublattice of ZrO2 due to the same ionic charge and similar cationic radius.

ESR-Zirconia supported V2O5 catalyst with various vanadia loadingsSpectra are more intense when number of V4+ ions increased.Dipol-dipol interaction between them cause broadening of the spectral lines.The intensity of the signal due to Zr3+ defects decreases.

electron spin resonance (ESR)27

Samples are calcined at gradually increasing temperatures. More information on the nature of V4+ species responsible for the complex structure of the spectra.

1V/Zr, norrow and sharp signal is related to the presence of Zr3+ paramagnetic defects.K3V/Zr, has intense and well resolved samples g11=1.9247, g_=1.9736 and A11=186.18, A-=62.47 due to 51V hfs observed.

Presence of V4+ Ions in ZrO2 Matrix

1V/Zr3V/ZrStepwise calcinations.At temperatures above 1053 K, similar sequences of spectra was recorded.It indicates that in both cases V4+ ions occupy the same positions within the crystal lattice.

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ConclusionPhase transitions are observed. Metastable tetragonal monoclinicPhase transitions are influenced by additives.(vanadium and potassium).Vanadium stabilizes the metastable tetragonal phase of zirconia.Diffusion of the surface V4+ into ZrO2 matrix is strongly accelerated by phase transition.

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