Chemisorption Analyzers

ChemiSorb™ Series

The Versatility of theChemisorption Technique forCatalyst Characterization

Knowledge of surface chemistry and surfacestructure is essential in the design, produc-tion, and application of a catalytic material.The Micromeritics ChemiSorb 2720 and2750 quickly and accurately measure thequantity of adsorbed or desorbed moleculesallowing determination of these character-istics. The ChemiSorb 2720 makeschemisorption and physisorption analysesaffordable for applications in which owningan instrument had once been impractical.Furthermore, if analytical needs grow, thebasic system can be upgraded to providemore capability. The ChemiSorb 2750allows the same analyses as the ChemiSorb2720 with the added advantages of higherprecision, faster throughput, and more convenience in accommodating a variety of experiments.

Versatility in an InexpensiveChemisorption System – TheChemiSorb 2720

• Dual ports, one for analysis and one forsample preparation.

• Built-in sample cooling fan, four carrier gasinlets, and one prep gas inlet.

• The basic instrument can measure percentdispersion, active metal area, crystallitesize, and quantify acid and base sites usingpulse chemisorption. Physisorption testsinclude BET and Langmuir surface area,and total pore volume.

• An optional access fitting allows theChemiSorb to utilize a mass spectrometeror other external detector for identificationof desorbed species or reaction products.

Economical Chemisorption Analyses

ChemiSorb Series Chemisorption Analyzers

Higher Precision andVersatility – The ChemiSorb2750

• Dual-function sample ports can be used aseither a sample port or degas port. Oncethe sample has been degassed, reduced, orotherwise prepared, the port is switched to“test” mode for analysis. Possible contami-nation of a prepared sample by exposureto the atmosphere is eliminated.

• Higher precision, repeatability, and repro-ducibility are provided by the incorporationof an injector loop valve in addition to the injection septum. The loops are easilyexchanged to provide different injectionvolumes. Electrically activated inlet valvesallow the use of gases containing H2, CO,O2, N2O, NH3, liquid vapor sources, orother adsorptives.

• Three built-in prep gas inlets and fourcarrier gas inlets allow for a variety ofexperiments without having to disconnect,reconnect, and purge gas lines.

Added Capability – OptionalChemiSoft TPx System

• Optional ChemiSoft TPx System (temperature-programmed controller and software) expands the capabilities of the ChemiSorb 2720 and 2750 toinclude temperature-programmed reac-tions, data archiving, and advanced datareduction and reporting options.

• Expanded physisorption capabilityincludes multipoint BET surface area.

ChemiSorb 2720

ChemiSorb 2750

TPx Controller and Furnace

Typical ChemiSorbApplications

Catalysts – The active surface area and porestructure of catalysts have great influence onreaction rates and yield of product. Limitingthe pore size allows only molecules ofdesired sizes to enter and leave; creating aselective catalyst that will produce primarilythe desired product. Chemisorption experi-ments are valuable for the selection of catalysts for a particular purpose, qualifica-tion of catalyst vendors, and the testing of a catalyst’s performance over time to establishwhen the catalyst should be reactivated or replaced.

Fuel Cells – Platinum-based catalystsincluding Pt/C, PtRu/C, and PtRuIr/C may becharacterized by temperature-programmedreduction to determine the number of oxide phases or by pulse chemisorption tocharacterize the metal surface area, metaldispersion, and average crystallite size.

Partial oxidation – Manganese, cobalt, bismuth, iron, copper, and silver oxides areoften used for the gas-phase oxidation ofammonia, methane, ethylene, propylene,etc. Temperature-programmed oxidationand temperature-programmed desorptionmay be used to measure the heat of desorp-tion of oxygen from these catalysts and theheat of dissociation of oxygen from themetal oxide.

Catalytic cracking – Catalytic processesare used extensively for refining petroleum.Acid catalysts such as zeolites are used forcatalytic cracking and are often character-ized using ammonia chemisorption andtemperature-programmed desorption fordetermining the number and strength of theacid sites.

Catalytic-reforming catalysts containingplatinum, rhenium, tin on silica, alumina, orsilica-alumina are used for the productionof hydrogen, aromatics, and olefins. Thesecatalysts are often characterized usingpulse chemisorption techniques to determinethe number of active sites, the percent metaldispersion, and average crystallite size.

Isomerization catalysts such as small-pore zeolites (mordenite and ZSM-5) containing noble metals (typically platinum)are used to convert linear paraffins tobranched paraffins and thus increase theoctane number and value for blending gaso-line. Temperature-programmed reductionand pulse chemisorption are often combinedto characterize these catalysts.

Hydrocracking, hydrodesulfurization,

and hydrodenitrogenation catalysts aretypically composed of metal sulfides (nickel,tungsten, cobalt, and molybdenum).Hydrocracking catalysts are used for processing feeds containing polycyclic aromatics that are unsuitable for typicalcatalytic cracking processes. The hydro-cracking process is used for upgradingthese low-value products to gasoline anddiesel fuel. Hydrodesulfurization and hydro-denitrogenation are used for removing sulfur and nitrogen, respectively, frompetroleum feeds. Both sulfur and nitrogenare catalytic poisons and also are thesource of pollution (acid rain) if they arenot removed from gasoline and diesel fuel.Temperature-programmed reduction andoxygen chemisorption are used to charac-terize the oxide phases and active surfacearea of these materials.

Fischer-Tropsch synthesis uses cobaltand iron-based catalysts to convert syngas(carbon monoxide and hydrogen) to hydrocarbons larger than methane. TheFischer-Tropsch processes are of greatimportance as they provide hydrocarbonsthat are rich in hydrogen and do not containsulfur or nitrogen. These hydrocarbons are apotential liquid fuel that is easily transportedand distributed, and can then be reformedto hydrogen to supply fuel cells. These catalysts are often characterized by pulsechemisorption and temperature-programmeddesorption to determine the metal surfacearea and the average size of the metal crystallites.

Theory and Design

The Analytical Technique

The ChemiSorb 2720 and 2750 both utilizethe dynamic (flowing gas) technique ofanalysis. The quantity of gas adsorbed fromthe gas stream by the sample is monitoredby a downstream thermal conductivitydetector (TCD). The temperature and pres-sure at which adsorption/desorption occursis either known or monitored. The instru-ments can be used to study physical orchemical adsorption. Preparation usually isaccomplished by flowing either an inert orchemically active gas over the sample.After preparation, another gas is selectedfor analysis. Prep and carrier gases typical-ly used to allow both physical and chemicaladsorption experiments are He, Ar, N2,He/N2 mixtures, H2, and O2, some servingas both prep and carrier.

Chemical Adsorption

Any of a number of reactive gases such asanhydrous NH3, CO2, CO, H2, N2O, O2, andH2S can be used to react with the activesurface. A series of injections of a knownquantity of reactive gas is injected into aninert gas stream that passes through thebed of catalysts. Downstream from thereactor is a detector, which determines thequantity of reactive gas that is removedfrom each injection. Chemisorption testsideally are made with the sample at a tem-perature such that only chemisorptionoccurs. The active surface of the sample issaturated when the detector indicates thatthe total quantity of subsequent injectionspasses through the sample bed without any

loss. The sum of the injected quantity minusthe quantity of gas that passed withoutadsorption equals the quantity adsorbed.

Unlike physical adsorption, the injected gas chemically adsorbs only on the activesurface and not on the support. Thus, thenumber of gas molecules required to coverthe active surface area, once determined,leads directly to the active surface area.Applying the stoichiometry factor for thegas/metal reaction yields the number ofaccessible atoms of active metal.Furthermore, using the total quantity ofactive metal per gram of catalyst material(determined from the manufacturing formula) leads to the determination of thepercent dispersion of active metal. Usingthe information gathered plus the density ofthe metal, the size of the metal crystallitecan be estimated if it is assumed that theseparticles have uniform geometry of knownvolume-to-area ratio.

Physical Adsorption

The surface area of granulated and powderedsolids or porous materials is measured bydetermining the quantity of a gas requiredto form a monomolecular layer on a sample.Physical adsorption tests typically are per-formed at or near the boiling point of theadsorbate gas; N2 being most common with a liquid N2 bath being used to maintainthe analysis temperature. Under these con-ditions, a nitrogen and helium mixture of 30 volume percent nitrogen achieves thepartial pressure condition most favorablefor the formation of a monolayer ofadsorbed nitrogen at atmospheric pressure.

Under such specific conditions, the areacovered by each gas molecule is knownwithin relatively narrow limits. The area ofthe sample is thus calculable directly fromthe number of adsorbed molecules, whichis derived from the gas quantity at the pre-scribed conditions, and the area occupiedby each. Additionally, atmospheric pressureand ice water temperature may establishappropriate conditions for an n-butane andhelium mixture. Other gases at other condi-tions are also usable.

Flowmeter Digital Display of TCD Signal,Temperature, or Integrated Area

Cold TrapAnalysis Port Shown with

Optional Furnace and Controller

PreparationPort

Digital Display of TCD Signal,Temperature, or Peak Area

IntegratedFlowmeter

Push Button Selectionof Prep, Loop, and

Carrier gases

Dual PortDesign

Loop forPulse Dosing

ChemiSorb Features 2720 2750

Analysis Ports 1 2†Preparation Port 1 †Injection Septum Y YInjection Loop YSample Reactor Quartz QuartzGas Inlets

Carrier 4 4Preparation 1 3Loop 1Temperature Control

Integrated 2‡ 2Max Temperature 400 °C 400 °CWith TPx option 1100 °C 1100 °CFan-assisted Cooling 1 2Standard Analyses

Pulse Chemisorption Y YPhysisorption Y YChemiSoft TPx Analyses

TPR Y YTPD Y YTPO Y YPulse Chemisorption Y YPhysisorption Y YLoop Calibration YChemiSoft TPx Reports

% Metal Dispersion Y YMetal Surface Area Y YAverage Crystallite Size Y YFirst Order Kinetics Y YSingle-Point Surface Area Y YBET Multipoint Surface Area Y YLangmuir Surface Area Y YTotal Pore Volume Y Y

†Dual function Analysis/Preparation ‡One dedicated controller for preparation port and one

dedicated controller for the analysis port

Push Button Selection ofCarrier and Preparation Gases

Flow Path Options

Sample Thermocouple

DetectorSignal Out

Four CarrierGas Inlets

Optional TPxFurnace Accessory

Integrated Fan for RapidCooling of the FurnaceChemiSorb 2720

ChemiSorb 2750

TPx Option

User-SelectableFlow-Path Options

Sample Thermocouple

Cold TrapFour CarrierGas Inlets

Exhaust Ports

Loop Gas

ThreePreparationGas Inlets

DetectorSignal Out

Temperature-Programmed Chemisorption Option

ChemiSoft TPx System

When the optional programmable furnacesystem and accompanying ChemiSoft TPx

software are added to the 2720 or the 2750,another category of chemical adsorptiontesting can be performed –—Temperature-programmed reactions reduction (TPR),oxidation (TPO), and desorption (TPD).

Temperature control is provided by a furnace that operates from ambient (20 °C)to 1100 °C, and is able to produce tempera-ture ramps of up to 50 °C/min within the 20to 500 °C range, 30 °C/min within the 500 to750 °C range, and up to 10 °C/min in the 750to 1100 °C range. The furnace controllercan be programmed to provide multipleramps and soak times.

Temperature-programmedChemisorption

Temperature-programmed chemisorptionprovides information about adsorptionstrength when a catalyst is at working condition or at an elevated temperature.TPD analyses determine the number, type,and strength of active sites available on thesurface of a catalyst from measurement ofthe amount of gas desorbed at various tem-peratures. During a TPR analysis, a metaloxide is reacted with hydrogen to form apure metal. TPR determines the number ofreducible species present in the catalystand reveals the temperature at which

reduction occurs. TPO examines the extentto which a catalyst can be reoxidized andmeasures the degree of reduction of certain oxides.

ChemiSoft TPx Software

Included in the Temperature-ProgrammedChemisorption option is Micromeritics’ChemiSoft software that can be used to simplify chemisorption and physisorption aswell as temperature-programmed analyses.The software tracks and records time, mon-itors and records the analytical temperatureand detector output, creates and organizesdata files, reduces collected data, and pro-duces a variety of user-defined reports.Advanced peak integration capabilitiesassure reliable results.

With ChemiSoft, you can create and storestandard sets of analysis conditions forguiding frequently performed analyses.Analysis and prep conditions also arereported to provide a record of theenvironment under which thereported data were collected; thisalso assures faithful repeating ofan experiment if required. Cut-and-

paste and data export features simplifymoving data to reports or incorporatingchemisorption data with data from otheranalytical techniques.

ChemiSoft TPx software can be set up to runindependently of the instrument. This meansthat data files can be reviewed, calculationparameters changed, and reports generatedon any computer anywhere, anytime.

For the novice operator, the software fea-tures prompts for each step in the analysisprocess, literally talking the user throughan analysis sequence. When you are readyto move up to Micromeritics’ moreadvanced AutoChem 2920 or ASAP 2020Chemi, or to incorporate other Micromeriticsproducts into your laboratory, your operatorswill find that the format of the operatingsoftware is the same from product to product, thus training time is minimized.

The integrated Peak Editor is a valuable tool for rap-

idly integrating the TCD signal. Each peak is clearly

marked to show the peak start, end, maximum, and

baseline. A peak summary table is also provided.

The Chemisoft TPx report system features

standard reports for Pulse chemisorption,

BET surface area, Langmuir surface area,

Total pore volume, First-order kinetics, and

graphical reports.

The graphical reports can be customized by the user to show

company logos, user-selected fonts, and user-selected line colors.

Multiple experiements are easily

viewed to create overlay reports.

Data Reduction and ReportingVersatility

The basic instrument without theTemperature-Programmed Chemisorptionoption provides two ways to obtain data:

• Front panel meter readout• Chart recorder monitoring the analog

output from the thermal conductivitydetector

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visit Micromeritics’ web site at www.micromeritics.com,

contact your local Micromeritics sales representative, or

our Customer Service Department at (770) 662-3636.

The detector signal can be plotted versus temperature.

This allows the user to easily compare temperature-

programmed analyses for multiple samples.

Data are reduced and reported auto-matically by the ChemiSoft TPx

software, which is part of theTemperature-ProgrammedChemisorption option andcan be used with eitherChemiSorb instrument.Reports include single- and

multipoint BET surface area,percent dispersion, peak area

volume, calculated stoichiometryfactor, gram molecular weight, cross-

sectional area, calculated metal density,active (metallic) surface area, active parti-cle (crystallite) size, and activation energy(first order kinetics).

When used with the ChemiSorb 2750, addi-tional reports on Injection loop calibration,Injection loop volume with temperaturechange, and calibration error are available.

Other functions of ChemiSoft:

• Allows control of units, axis scales, andreporting range

• Prints report to screen, printer, or file (text only)

• Cut-and-paste capabilities• Capture displayed plots as a series of

x-y coordinates• Capture tables from screen as ASCII

text files• Integrates detector signals both automati-

cally and manually• Displays and prints peak graphs and

reports• Establishes calibration curves for calcula-

tion of unknown sample concentrations• Reprocess stored analysis data using

different parameters• Exports data in ASCII text format for

use in other applications• Allows for off-line data manipulation• Provides the ability to monitor two

instruments from one computer• Monitors and records furnace temperature

The ChemiSoft TPx accessory allows the user to

acquire the detector signal, the sample temperature,

and the furnace temperature. These siganls can then

be included graphically in reports.

Complex TCD signals can be deconvolved to provide

valuable insight and demonstrate that the composite

signal is the sum of two peaks.

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