PROJECT DESCRIPTION

Supported

catalysts

are

essential

components

in

a

variety

of

industrial

processes,

ranging

from

catalytic

converters

to

production

of

new

drugs.

The

performance

of

a

catalytic

process

is

intimately

related

to

the

catalyst

design

-

uniform,

egg-

yolk,

egg

-

shell

and

egg

-

white

metal

profiles.

It

is

generally

believed

that

the

metal

profile

is

controlled

by

the

conditions

that

are

applied

during

impregnation

where

the

metal

contacts

with

the

solid

support

for

the

first

time.

However,

experiments

have

shown

that

drying

may

also

significantly

impact

the

metal

distribution

within

the

support.

Therefore,

to

achieve

a

desired

metal

profile

we

need

to

understand

both

impregnation

and

drying.

Controlling

the

drying

conditions

can

enhance

catalyst

performance.

PROJECT GOALS

The

goal

of

this

project

is

to

develop

a

fundamental

understanding

of

unit

operations

during

catalyst

preparation,

so

we

can

predict,

control

and

optimize

metal

distribution

and

dispersion

in

supported

catalysts.

Therefore,

we

can

provide

our

partners

with efficient tools to monitor and control the final quality of supported catalysts.

SUMMARY OF STUDIES

In

this

work

we

have

developed

a

theoretical

model

for

drying

which

we

have

validated

experimentally.

In

this

model,

we

have

taken

into

account

heat

transfer

from

the

hot

air

to

the

wet

support,

solvent

evaporation

in

the

support,

convective

flow

towards

the

support

external

surface

due

to

the

capillary

force,

as

well

as

metal

diffusion

and

deposition

due

to

adsorption

and

crystallization

(see

Figure

1a).

In

general,

the

convective

flow

is

the

main

driving

force

to

transport

the

metal

component

and

the

solvent

towards

the

supports

external

surface

(t=500s

in

Figure

1b),

while

the

back-diffusion

causes

metal

to

transport towards the support center (t=1000s in Figure 1b).

Figure 1. (a) drying mechanism, (b) simulation of the evolution of the metal distribution during drying

We

also

developed

a

theoretical

model

to

predict

the

drying

process

for

high

metal

load

conditions;

this

was

accomplished

by

building

upon

a

model

that

was

established

for

low

metal

loadings.

It

is

found

that

the

drying

mechanisms

for

low

metal

loading

conditions

and

high

metal

loading

conditions

are

quite

different.

This

model

is

applicable

for

higher

concentrations

of

nickel

nitrate

(above

0.1

M).

It

included

the

effects

of

the

metal

concentration

on

the

solution

density,

viscosity,

surface

tension,

vapor

pressure

and

the

volume

ratio

of

metal.

Good

agreement

was

found

between

experimental

and

simulation

post- drying metal distributions for this model using nickel nitrate. (see Figure 2).

Figure 2. Experimental results compared to post drying metal distributions using simulation for two different metal loadings

(1.0 M and 3.0 M). (T=80C, uniform initial condition)

In

our

work,

we

are

interested

in

investigating

the

importance

of

the

physical

properties

of

the

solid

support

(porosity,

pore

size

distribution,

particle

size)

and

liquid

solution

(pH,

ionic

strength,

initial

metal

precursor

concentration),

the

nature

of

interactions

that

exist

between

the

dissolved

metal

and

the

solid

support

(physical

adsorption,

crystallization,

ion

exchange,

film-breakage,

pore-blockage),

and

their

effects

on

the

distribution

and

dispersion

of

the

active

metal.

We

have

examined

the

distribution of various metals such as Nickel, Copper, Barium, and/or Palladium on Alumina (see Figure 3).