Synthesisand Structural Analysis of Aluminophosphates
(Zeoliteand Zeolite-Type Materials)
Zeolite and Zeo-type materials 4
AlPO4-5 Aluminophosphate 4
Metal Substituted Aluminophosphates 5
Literature Review 6
Results and Discussion 8
Reaction, SEM, and XRD results for AlPO4-5 9
Reaction, SEM and XRD results for SAPO-5 12
Reaction, SEM, and XRD results for MgAPO-5 14
Graphically Comparison of Crystallinity and XRD Pattern 16
Metal-substitutedaluminophosphate (MeAPO-5) is one of the zeolites that was developedby the union of Carbide Corporation through the process of inclusionof metal ion, Me into the framework of AIPO. The process ofhydrothermal synthesis is used to crystallize organic structure ofMeAPO-5 crystallizes to form an AFI-type structure. Substitution ofAL by Me takes places in a reaction medium. Different molecules ofMeAPO-5 such as Me, Mn, Co and Fe can be synthesized hydrothermally.This report gives a description of the process as well as the resultthat is obtained based on the metal ion that is used in thesubstitution. Esterification reaction is also explained in the paperand its contribution to the analysis of aluminophosphates. Itinvolves the reaction of the Acetic acid with Ethanol while usingSulfuric Acid as a catalyst leading to the production of EthylAcetate and water. The primary results of this study are discussed inthe paper, and they include the reaction result, SEM and XRD outputfor crystallinity and molar compositions of different Zeolite andZeolite-Type Materials.
IntroductionZeolite and Zeo-type materials
Zeoliteand Zeo-typematerialsare inorganic substances that are comprised of a wide range ofcrystallinesolids that have porous structure interconnected to form atetrahedral network.The frame structure of these materials is based on a complex networkhaving the interconnectivity of Si-rings along with the heteroatom (Ti, Al, Fe, B) substitution onto the Si or non-Si equivalent sites.Graphical theory shows that the elements that form the zeolitecontain approximately, 104 chemicals that are crystallographicallystructured with a 3-dimensional network that is interconnected withthe tetrahedral vertices. Some of these elements are syntheticallycreated while other exist naturally (Čejka & Bekkum, 2011). Theopen framework structure of zeotypes is formed using guest moleculesuch as the organic based cation which is also referred to asstructure-directing agent (SDA).The SDA performs its role byfacilitating the formation the precursors of molecular scale thatcauses nucleation growth and initiate the process of crystallizationof open-framework materials(Selvam& Sakthivel, 2013).
AlPO4-5is an example of Aluminophosphate, its AFIstructure consist of PO4 tetrahedronsand AlO4that alternate with each other to create a one-dimensional framework.Also, the structure has electrically neutral cylindrical pores with auniform cross section of 7.3 thatcan be stretched in the direction parallel to the crystal axis.(Kimura,2012 Mintova, Mo, & Bein,2011 Karanikolos,2011).AlPO4-5is an important material in applications that uses shape-selectivecatalysis, isolating technology and in non-linear optics(Busca,2014).It can be synthesized by various techniques such as hydrothermalsynthesis andmicrowave heating. Different parameters are used during its synthesiswhile taking into consideration various aspects such ascrystallization time, the initial formation of the precursor solutionand temperature. These aspects are crucial in controlling themorphology of AlPO4-5(Selvam& Sakthivel, 2013).
Theseare formed by incorporating the ions of transition metals into thestructure of Aluminophosphate through the process of substitution.Thirteen elements are integrated into AlPO-5together with transition metal ions such as zinc, iron, titanium,cobalt and manganese. Molecular sieves of silicon- aluminophosphateand sites are included in the transition metal ion to aid indesigning of the novel catalyst. The paramagnetic species areinserted into molecular sieves to generate catalytically reactivesites or species. Different activation or pre-treatment process arespecifically used to achieve valence state of reactive metal ionoften paramagnet. There are three different methods used for theincorporation of transition metal ions namely: Ion-exchange method,Impregnation, and Isomorphous substitution.
Substitutionis the most commonly used method, here salt of transition metal ionis combined directly in the synthesis mixture. According to Flangenet.al (1986 and 1988), substitution involves the transition of metalions into the framework of different structure types Since variousmaterials of transition metals can be merged into the structure ofaluminophosphate. (Rajic,2015 Szostak & Stepto, 2012 Sundaravel, 2015 Flanigen,1986Flanigen,1988Hartmann &Kevan 1999).
Anexample of a metal substituted aluminophosphates is MeAPO-5.Themolecular sieves of MeAPO-5 are created using a template of glucosemesopore which has various applications such as X-ray fluorescenceand diffraction. The Mesoporous have varying sizes which range fromof 5 to 30 nm these pores improve the performance of the MeAPO-5 byincreasing its affinity catalytic reactions.MeAPO-5 has several advantages over Commercial Zeolites and is mainlyused in industrial applications for instance in the production oflight emitting diodes. They are also used in home applications suchas rodent control.MeAPO-5 is mixed with food mixture and givenrodents for consumption. The acid present in the digestive system ofrodent mixed with phosphide and the toxic gas of phosphine isgenerated (Foster, 2011).
Commercialzeolites as the catalyst possess a number of advantages overconventional catalysts they are less corrosive, they exhibit highthermalstability, and they have minimal disposal problem, the advantages ofzeolite are attributed to their adaptability to a large number ofcatalysts and their strength of acidity. The primary limitation ofzeolite is that it can be deactivated through steric blockagesecondary products or permanent adsorption.
Numerousstudies have been conducted on CoAPO-5, FeAPO-5, MgAPO-5 and SAPO-5,to determine the manner in which they are synthesized andhydrothermal method and also to establish their level of thecrystallinity, the morphology. The previous works on these materialsas well as the effects of their synthesis are described below:
CoAPO-5-Hydrothermal method has been used to study the molecular sieve ofCoAPO-5 through the application of time-resolved in XAS, Raman, SAXS,and UV−vis. In these studies, XAS indicates the transformation ofCo2+ in two phases and the use of heat to speed the process. Thefirst phase involves the conversion of the octahedral structure intoa tetrahedral structure, and this is followed by the formation ofBragg peaks as Co2+ is added to the network of Al−O−P. The secondphase involves a rapid transformation of the remnants of Co2+ at theend of the reaction. Raman spectroscopy is used to detect Al−O−Pbonds that are formed in the initial stages of the reaction. SAXS isused to identify the distribution of gel particles before the processof crystallization begins. The purpose of synthesizingCoAPO-5 using hydrothermal method increases the level of isomorphoussubstitution Co2+ ionsinto the framework of AFI (Byrappa & Yoshimura, 2013).
FeAPO-5,there has been an investigation of ionothermal crystallization of themolecular sieves of FeAPO-5 in the medium containing H3PO3whichfacilitates the formation of FeNKX-2which is an intermediate phase in the creation of a metastable.FeNKX-2 which is formed through the addition of Fe3+then transforms into FeAPO-5that exists in a crystallinephase and has an open-framework. A Polar ionic liquid is used todissolve the raw materials(MacIntosh,2012).
MgAPO-5has different content of magnesiumand is synthesizedby means of the hydrothermal which is characterized using thetechniques of XRD, IR, NH3-TPDand ICP-AES.A study of characterization data of the synthesis showsthe occurrence of isomorphous substitution of Mg for Al in a mediumconsisting of pure AFI. The effect of the synthesis is the formationof MgAPO-5 which has two categories of acid sites, the weak and thestrong sites. The condition for the reaction must be controlled(Hassanvand,2013).
SAPO-5is a form of Mesoporous zeotype that is prepared using precursors ofsilatrane and alumatrane. The conditions of reaction and effect ofsilicon on the reaction depend on the temperature, reaction time andaging time which are all determined by experimental analysis. Thesample of SAPO-5 characterized by scanning electron microscopy andX-ray diffraction. The effect of its synthesis is the formation of anSAPO-5 zeotype that has an AFI structure and possesses a hexagonalsurface morphology on the outer side.
HydrothermalSynthesis affects both the Crystallinity and Morphology of thematerials that are formed using this method, the hydrothermal timeand temperature directly influences the type of Crystallinity thatwill be formed. For instance, longer hydrothermaltime and high temperatures improve the crystallinity of the materialand promote it colloidal stability. Also, the morphology of particlesof the particles greatly depends on temperature. Studies show thatincrease in temperature leads to the formation of nanostructuresthus forming a morphology consisting of dispersed prisms.
TheMeapo-5 has got an acidic effect it is reported that theisopropylation of benzene with 2-propanol over alkaline earth metalsubstituted MeAPO-5 (Me = Mg, Ca, Sr and Ba) molecular sieves”.Since the selection of benzene and cumene conversion are in the givenorder: "Mg >Ca>Sr>BaAPO-5".Among all thesecatalysts, the presence of MgAPO-5 is more strength and activebecause of the presence of acid sites as compared to another catalyst(Waghmode,Saha,Kubota,2011).
UnitCell Expansion Method can be used to incorporate metal ionssuccessfully, in this method no contraction and expansion occurs. Forexample in the synthesis of MeAPO4-5, unit cell keeping itself intothe experimental error of system thus making it easy to verifyMeAPO4-5 substitution using chemical analysis and unit cell expansionmethod (Byrappa & Yoshimura, 2013).
Theesterification of acetic acid with ethanol has been studied by usingdifferent mono-metal ion substituted AlPO4-5 including (SAPO-5,CoAPO-5, FeAPO-5, and MgAPO-5) at 75oC with a catalyst mass of 1.5gand molar composition of (Al: 1.3 P: xMe: 1.2TEA: 100H2O).
Results and Discussion
Thegeneral framework of zeolite and zeotype materials consist oftetrahedral units that are bonded together to form a network of atomsof aluminum, magnesium or silicon depending on the type of compound.This research was based on ahydrothermal synthesis of various Aluminophosphatesmaterials. These materials undergo structural and morphologychange which is accompanied by the variation of crystallinity whendifferent metals are introduced into their components. The resultsobtained from the study include the reaction results, X-Raydiffraction (XRD) and SEM results, the three sets of results can beused to analyze the crystallinity of the materials (Byrappa &Yoshimura, 2013).
Reaction, SEM and XRD resultsfor AlPO4-5
Thereaction results show that the crystallinity of AlPO4-5 depends onthe effect of heat and the change in water composition on itsmorphology during the process of synthesis. High temperatures speedup the reaction. However, prolonged heating has a neutral effect onthe formation of crystal morphology. Water composition alsoinfluences the morphological change this is because AlPO4-5 issynthesized by using C2H5)3N∶Al2O3∶P2O5∶xH2Owhich is a gel composition whose performance is based on the watercontent. The amount of water on the gel used at the beginning of thesynthesis process determines whether it will be a success or not.This is because low water content leads to the achievement of betterconversion of various reagents forming AlPO4-5,this reduces the time taken to complete the reaction. Research showsthat gel composition having a water content of 20 H2Oor 10 H2Otends to form AlPO4-5with thin hexagonal platelets. The low moisture content of gel duringsynthesis is beneficial since it results into AlPO4-5that has longer self-life.Results have shown that the size, orientation and morphology ofAlPO4-5 crystals can be controlled by changing the gel composition,heating power, crystallization time, water content and magnitude oforganic template.
TheSEM results for AlPO4-5 shows that it is microporous and has acrystalline structure. It is formed hydrothermally by reacting of Aland P in a medium that contains organic sources. SEM micrographs areobtained shows that there is nucleation on its surface which changeswhen the temperature of the heat is varied. From the result we get toknow that crystals grow gradually up to a point where it forms anorientation similar to that of glass, the results further indicatesthat the crystals the AlPO4-5 grows freely and is composed of twoparts that grow in the direction opposite to one another. The twoparts of the crystals are a mirror line of each other and haveidentical structure (Eon, 2016).
TheXRD patterns obtained from AlPO4-5 which is synthesized using a gelat a temperature of 150 °C shows that AlPO4-5 has amorphousstructure after about half an hour into the process of hydrothermalsynthesis. This changes with time up to the point where the structurebecomes crystalline. When AlPO4-5is subjected to a longer period of hydrothermal synthesis, thecharacteristic XRD reaches its, and the sizes of the crystals can beestimated using the patterns of XRD. The increase in hydrothermaltime results into crystals of larger sizes.
Themorphology and structure AlPO4-5 are shown in the figures below thevariation depends on the amount of water in the gel.
APO4-5with molar composition of (Al:1.3 P:1.2TEA: 100H2O)
APO4-5with molar composition of (Al:1.3 P:1.2TEA: 200H20)
(APO4-5with molar composition of (Al:1.3 P:1.2TEA: 300H2O)
APO4-5with molar composition of (Al:1.3 P:1.2TEA: 400H2O)
Reaction, SEM and XRD resultsfor SAPO-5
Thereaction results show that the SiO2 magnitude is varied mole ratiofrom 0 to 1.0 of the given SiO2 to Al2.The crystals SEM images thatare obtained by using various contents of silicon are representingthe sample produced in the absence of silicon in reactant gel and issimilar to the long rod-like hexagonal structure, which is also thecharacteristics of AlPO4-5 having an AFI structure. At the time ofloading SiO2 into the gel chemical composition, the morphology ofcrystal became platter like hexagonal and short structure (Eon,2016).
SEMresults shows that the SEM images for SAPO-5 are obtained from theAl2O3:2P2O5:0.2SiO2:1.5TEA:750H2O reaction gels which are aged. Thegel is prepared by heating it up in a container and stirringcontinuously as it boils, the temperature of heating is maintained at190 C. The PH of the gel mixture is kept neutral, while the ratio ofAl2O3 to P2O5 used is 1:2.This process leads to the formation ofsmall crystals SAPO-5, the aging time is prolonged due to a largenumber of the nucleation sites that are involved in the reaction.When the aging time is increased exponentially less uniform crystalsare formed though their sizes remain small (Eon, 2016).
TheXRD patterns of SAPO-5 at the initial stages of hydrothermalsynthesis indicates that its structure is pure since there no tracesof impurities. However as the process of synthesis advances beyond 24hours where aging starts, some small amount of impurities begin toshow up. These impurities mainly consist of tridymite phase(Rajic,2015). The formation of SAPO-5 is greatly influenced by agingtime. It has contents of SiO2, in a mole ratio of SiO2 and Al2O3 thatis loaded to the gel to form a perfect and highly crystalline sampleof SAPO-5.The SAPO-5 having the temperature of 600 degree Celsius isshowing high-intensity value.In the case of SAPO-5, as thetemperature increases the intensity value also increase and themaximum peak value is present at high temperature and minimum peakvalue present at low temperature (Utchariyajit& Wongkasemjit, 2010).
Thevariation of structure and morphology of SAPO-5 based on the level ofwater content is as shown in the diagrams below.
SAPO-5with molar composition of (Al: 1.3 P: 0.8Si: 1.2TEA: 100H2O)
SAPO-5with molar composition of (Al: 1.3P : 0.05Si: 1.2TEA: 100H2O)
SAPO-5with molar composition of (Al: 1.3P: 0.05Si: 0.2TEA: 100H2O)
Reaction, SEM and XRD resultsfor MgAPO-5
Reactionresults of MgAPO-5 With Molar Composition show that The samples ofcrystalline MgAPO-5 were synthesized using the different molarcomposition of magnesium in a different mole ratio from 0.0 to0.11.Since the overall moles of Al and Mg is a constant value butalways similar to the total moles of the phosphorous. The value of Mgmolar ratio in the gel is equal to zero relates to the purifiedAluminophosphate. Molar ratio y=Mg/(Mg+Al+P) significantly in thesolid and during gel starting the reaction. Hence as the content ofMg in the solid is increased then the molar fraction value in the gelalso increased or to say linear relationship present in between Mgcontent and a molar fraction. This indicates that specifically Mg issubstituted in the aluminum. This is considered as mechanismpresented by Flanigen et.al particularly for the method ofsubstitution in divalent metal in the framework of Aluminophosphate(Kimura, 2012).
SEMresults of MgAPO-5 shows that it has a hexagonal crystal which is acommon property of the AFI materials. The surface of the MgAPO-5appears to be having pores, this caused by the fast speed of growthwhich weakens the structure of the reaction medium. XRD analysis ofMgAPO-5 synthesis result shows that heat treatment has aninsignificant effect on its structure, crystallinity, and size. Thestructures of MgAPO-5 are as follows:
MgAPO-5with molar composition of (Al: 1.3P: 0.2Mg: 0.2TEA: 100H2O)
FeAPO-5with molar composition of (Al: 1.3P: 0.2Fe: 1.2TEA: 100H2O)
Graphically Comparison ofCrystallinity and XRD Pattern
Thegraph below illustrate the XRD pattern of various materials itindicates the high purity and crystallinity of CoAPO-5 and CoSAPO-5the two lacks peak if relative impurities are present. However, inthe case of SAPO-5, the presence of metal oxide transition isobserved. The degree of crystallization varies according to Cocontent, the crystallinity of CoAPO-5 and CoSAPO-5 significantlyimproves as the ratio of Co/P increase from 0.01 to 0.05, while inthe case of SAPO-5, the crystallization degree decreases withincrease in Si content (MacIntosh,2012). In the graph below, the effect of morphology, crystal phase,and crystallinity are examined, and the outcomes of XRD patternindicates that all the samples of SAPO-5 produced in the similarcrystallization condition.
Thecrystallinity of COAPO-5, SAPO-5 and CoSAPO-5 as the metal molarpercentage increase. Shown are (210,(002) and (102) reflections.
Thegraph below illustrates the growth of crystal of CoAPO-5 andSAPO-5.The crystals have a diameter ranging between 50 micrometersand 400 micrometers. The X-ray diffraction pattern indicates that thecrystal structure of CoAPO-5 is similar to that of ALPO4-5.Thecomposition of both CoAPO-5 and SAPO-5 is tested using X-rayfluorescence. The graph shows that an increase in Co and Si contentresults into an increase in the molar ratio. The pattern of CoAPO-5and SAPO-5 growth temperature is similar to 130 and 150 degreeCelsius as shown in 210 and 002 (Maschmeyer,2016).
XRDpatterns for CoAPO-5 and SAPO-5 prepared at varies growthtemperature.
Shownare the (210) and (002)
Thegraph below shows lattice expansion of MeAPO4-5.The metal ions areincorporated into the structure MeAPO4-5 through the method of unitcell expansion which involves the creation of pore in materialstructure thus creating a space where the metal ions are inserted.The process takes place in a chemical reaction.
Latticeexpansion as observed for MeAPO-5 and variation of a= b cellparameter
Itis observed that the surface area of material decrease at atemperature of 800 °C then abruptly increase at the temperature of 900 °C. The decrease in surface area is attributed to the process ofcalcination which occurs at the temperature of 800 °C. Calcinationcauses large shrinkage of the surface areas. The increase intemperature to 900 °C is attributed to the formation of ananocrystal of AlPO4.Since the space and gap in between nanocrystalis effected the pore volume and surface area. (Widayat,&Rachimoellah, 2011).
Inthe graph of the evolution of ethanol, conversion is plotted againsttime for different mono-substituted AFI catalysts. The resultsindicate that FeAPO-5 and MgAPO-5 have no effect on the reaction. Thecharge of iron used to synthesize FeAPO-5 is +3, and the charge ofthe magnesium used to synthesize MgAPO-5 is +2.
DifferentBi-metal ion substituted AlPO4-5 Including (CoSAPO-5) at 75oCwith a catalyst mass of 1.5g and molar composition of (Al:1.3 P: xMe: 1.2TEA: 100H2O).The graph below shows a reaction of a given cyclohexane and bi-metalion substituted in AlPO4-5, there is high a level of catalyticactivity in the reaction as compared to a single value of metal ionsubstitute that is analog. (Liu,2015)
Evolutionof ethanol conversion over CoAPO-5, SAPO-5 and CoSAPO5 materials
Anincrease in the mole ratio of ethanol to acetic acid causes the rateof conversion for acetic acid to increase since it uses surplusethanol. The kinetic reaction is improved through the use ofcatalytic membrane (Kirbaşlar, Baykal & Dramur, 2011).
Effectof catalyst loading on ethanol conversion
Turningwater is added to the gel to achieve the right concentration forreaction, the mixture is used to synthesize SAPO-5 whose aciditydepends on the concentration of the gel. When the volume of turningwater is decreased, the content of Si increases, concentrations ofhigher levels leads to the formation of crystalline material that ishighly purified (Eckenfelder, Bowers, & Roth, 2013).
Effectof silicon content on ethanol conversion
Hightemperature hastens the conversion rate a high temperature isachieved when the reactants are subjected to long contact time whichincreases ethanol conversion rate. The presence of water helps intemperature distribution across the structure of the elements used inthe in the reaction.
Influenceof reaction temperature on the ethanol conversion over SAPO-5
Thereis a significant variation between Zeolite Beta and SAPO-5 based ontheir applications Zeolite Beta is mainly used as a catalystreaction due to the advantage that it has over other catalysts whileSAPO-5improves the functionalities of polyurethane as well as the structureof the membrane(Szostak&Stepto, 2012).
Comparisonbetween zeolite and SAPO-5
Thesynthesis of reusable and stable SAPO-5 are investigated andconcluded that characterization of catalyst and the optimization ofthe reaction condition is set to explore the stability and propertyof higher activity in conversion profile of SAPO-5.
Aluminophosphatehas a wide range of applications however, they are mainly used as acatalyst. Some of the most commonly used catalysts are Zeolites, andzeotypes materials since they exhibit excellent catalytic activity.Besides, they are capable of reacting in mild-medium, a property thatmost of the conventional catalysts lacks (Maschmeyer, 2016). Thisstudy has revealed the special features of molecular sieves ofzeolites and zeotype materials which include porosity, acidity,surface area as well as hydrophilic properties. These properties havebeen represented graphically to enhance their visibility and alsofacilitate the interpretation of the structure of mostaluminophosphates. Their Catalytic activity is imparted to throughisomorphous substitutions of metal ions which are incorporated intotheir structure leading to the formation of metal substitutedaluminophosphates such as MeAPOs.
Thecharacterization, catalytic activity and synthesis of MeAPO-5 involvecomplex procedures such as the chemical reaction of Me (where Me canbe metal ions such as Mg, Mn Zn, and Co) and molecular sieves whichare made and characterized using SEM, XRD and other chemicalreactions (Szostak &Stepto, 2012). The XRD patterns of theMeAPO-5 before and after the ion exchange is the same hence there isno structural change. The SEM micrographs also indicate that themorphology remains the same throughout the process of hydrothermalsynthesis. However, the weight of the materials changes depending onthe temperature of the heat that they are subjected. The study hasalso shown that MeAPO-5 formed through metal ion-exchanged can beutilized as potential catalysts for the synthesis of various caluminophosphates. This study shows that it is possible to controlthe phase of materials involved ion thermal synthesis molecularsieves by adding metal ions to the amines.
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