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East Afr. J. Biophys. Comput. Sci. (2022), Vol. 3, Issue. 2, 11-24  

 

 

*Corresponding author: 

  Email: jovineemma2007@yahoo.co.uk, +255 769910443 https://dx.doi.org/10.4314/eajbcs.v3i2.1S 

 
 

 

 

 

Effect of Pressure on Carbon monoxide Oxidation on Titania Supported Platinum Nanoparticles 

Catalyst 

Jovine Emmanuel 
 

University of Dar es Salaam, Mkwawa University College of Education, Department of Chemistry,, 

P.O.Box 2513 Iringa-Tanzania 

 

 

 

KEYWORDS:  

Activity; 

CO conversion; 

Particles; 

Platinum and titania 

 

 

 

ABSTRACT 

Thermographic testing methodology was developed to facilitate measurements of particle 

dimension and substrate influence in heterogeneous catalysts. A screening chip with 

several areas of less stress silicon nitride membranes which displays less heat conductivity 

and heat capacity was used. Heat produced during the reaction on catalysts deposited on 

membranes was established through IR camera which gave the value of the turn over 

frequency. Effect of pressure on CO conversion on titania supported Pt particles of 

different dimension was measured on 120 catalysts concurrently. The reaction was studied 

at various O2 and CO pressures at 170 ℃ and 240 ℃. At these temperature conditions, 

activity increased with increase of O2 and CO pressure, in agreement with previous 

reports.  

 

INTRODUCTION 

There is a fair idea on catalysis starting from 

ancient times. It largely contributes in a number 

of applications as in chemical, agricultural, food 

and pharmaceutical industries, manufacturing 

and energy transformation and environmental 

safety (Scheidtmann et al., 2001, Emmanuel, 

2022). Estimates indicate that above 90% of 

chemical production routes depend on a single 

or multiple catalytic pathways (Armor, 2011, 

Emmanuel and Hayden, 2022). Metal catalysts 

largely rely on substrate, shape and dimension 

of supported metal nanoparticles catalyst. 

Reports indicate that the reactivity of properly 

characterised supported catalysts are important 

in knowing the influence of particle dimension 

and substrate. A good case of such a catalyst 

revealing a greater substrate and particle 

dimension influence on reactivity is supported 

platinum (Pt) in low temperature conversion of 

tiny molecules like carbon monoxide (CO) and 

hydrocarbons (Liu et al., 2010). Platinum (Pt) is 

among the frequently used metal catalysts in 

enormous applications over the decades. 

Dobereiner reported the activity of Pt in 1800s 

where it was applied in the catalysis  of H2 and 

East African Journal of Biophysical and Computational Sciences 

Journal homepage : https://journals.hu.edu.et/hu-journals/index.php/eajbcs 
 

Hawassa University

College of Natural & Computational Sciences

Year 2021

Volume xx No xx

 

 
Research article

mailto:jovineemma2007@yahoo.co.uk
https://dx.doi.org/10.4314/eajbcs.v3i2.1S


East Afr. J. Biophys. Comput. Sci. (2022), Vol. 3, No. 2, 11-24 
 

12 

O2 in portable lamp (Somorjai, 1994). Besides, 

Pt related catalysts are applied in different 

reactions such as the transformation of aliphatic 

straight-chain organic molecules to aromatic 

molecules and branched molecules, in huge 

scale hydrogenation in chemical and petroleum-

refining industries and ammonia conversion 

(Somorjai, 1994). More significantly, it is used 

for CO oxidation and unburned hydrocarbons in 

car emissions control (Franceschetti et al., 

2003). Platinum catalyst, on the other hand, is 

the most commonly applied and active electrode 

in fuel cell technology (Franceschetti et al., 

2003). Although Pt is widely used in various 

fields, it is an expensive precious metal and less 

abundant which make its application in various 

technologies largely challenging (Cameron et 

al., 2003). Because Pt bare high cost, the 

priority has been its application at the atomic 

scale in heterogeneous catalysis. This includes 

the spreading of Pt particles on high surface area 

metal oxide substrates like Al2O3, TiO2 and 

Fe2O3 which reduce the quantity of Pt integrated 

in the catalyst (Somorjai, 1994). Supporting Pt 

lowers the catalyst expenses in addition to 

increasing effective surface area of the catalyst 

in addition, it strengthens catalyst’ particles. 

Substrates like TiO2 are directly involved in 

reaction pathways through reactants and 

intermediates activation thus, improving the 

activity. Pt catalysts on carbon is widely applied 

in PEMFCs technology (Emmanuel, 2022). 

However, application of Pt catalyst is affected 

because of the decline of catalytic efficiency 

due to particle disintegration, rusting of cathode 

substrate and CO inhibition (Kim and Jhi, 

2011). The decline of efficiency is because of 

greater interaction of Pt and CO which inhibits 

O2 from getting on the surface of a catalyst 

(Schubert et al., 2001; Molina et al., 2009; Liu 

et al., 2010). Carbon monoxide conversion 

reaction on Pt supported catalysts is widely 

investigated (Santra and Goodman, 2002; Liu et 

al., 2010; Slavinskaya et al., 2011; Allian et al., 

2012; Dobrin, 2012). It is known that because of 

strong interaction with oxygen and Pt surface, 

O2 adsorbs and break down to generate effective 

surface adsorbed atomic oxygen which 

combines with adsorbed CO to generate CO2 

(Bamwenda et al., 1997; Haruta, 2003; Gao et 

al., 2009). Carbon monoxide conversion on Pt 

proceeds very efficiently with a conversion rate 

dependent on CO and oxygen partial pressures. 

Previous reports show that the reaction needs 

chemisorbed oxygen and CO on Pt surface, a 

pathway termed as Langmuir-Hinshelwood 

mechanism (McCash, 2001; Kolasinski:, 2002; 

McClure and Goodman, 2009; Liu et al., 2010, 

Santos et al., 2010). Studies indicate that this 

reaction is influenced by  reactants pressure, 

coverage and surface temperature (Kolasinski:, 

2002). However, competitive adsorption among 

CO and O2 is reported. Although CO can adsorb 

on an O2 occupied surface, O2 cannot adsorb on 

CO occupied surface. With high CO occupied 

surface, the reaction is restricted by O2 thus, 

raising CO pressure inhibits the reaction 

because no extra adsorption sites for O2. 

However, at low CO occupancy, O2 adsorption 

proceeds rapidly and the reaction relies on 

surface coverage of CO and O2 (Kolasinski:, 

2002). Given the catalytic efficiency of Pt 

catalyst, the reactivity is hampered by CO 

inhibition in gas-phase CO oxidation thus, 

maximum CO oxidation to CO2 is attained at 

minimal CO surface occupancy (McClure and 

Goodman, 2009). In this regards, Pt catalysts on 

substrates are perceived as poor catalysts for 

small temperature CO conversion (Li et al., 

2008).  



East Afr. J. Biophys. Comput. Sci. (2022), Vol. 3, No. 2, 11-24 
 

13 

Studies indicate that Fe2O3 supported Pt 

nanoparticles catalyst exhibits unusual high 

catalytic properties for CO conversion at small 

temperature (Liu et al., 2010). The activity is 

associated with the capability of Fe2O3 to 

provide active oxygen during the reaction. 

Titania supported Pt nanoparticles less than 5 

nm show low activity for CO oxidation reaction 

(Rashkeev et al., 2007). Theoretical studies 

propose that Pt nanoparticles between 1 and 2 

nm dimensions are more effective for CO 

oxidation (Dobrin, 2012). Further reports 

indicate that Pt particles of 2 nm dimension are 

the best effective for CO conversion in 

comparison with those of 3 nm and 5 nm 

dimensions (Kageyama et al., 2013). 

Electrocatalysis benefits from combinatorial 

synthesis and thorough characterization of 

oxide-supported metal nanoparticle catalysts, 

readily enabling high-throughput screening of 

various reactions using electrochemical chips. 

However, applying analogous methods to 

heterogeneous catalysis is considerably more 

complex. A breakthrough solution, published by 

Emmanuel et al. (2019), utilizes a 100-channel 

microreactor array and mass spectroscopy to 

study the H2-D2 exchange reaction on thin-film, 

small-area alloy catalysts. For less complex 

reactions in which it is not important to establish 

selectivity, net activity established in the heat 

generating reaction through infrared 

thermography methodology is promising. This 

methodology was applied for testing of catalysts 

in the conversion of hydrogen and octane on 

high area catalyst samples (Emmanuel et al., 

2019). However, expansion of the methodology 

to arrays of properly characterised catalysts like 

metal supported electro-catalysts to achieve 

structure/activity influences is a challenge 

(Hayden, 2013). The considerably low surface 

area of planar catalysts needs an amplified 

sensitivity so as to identify the heat produced in 

the course of a reaction. The current study 

reports the impact of pressure on reactivity of 

titania supported Pt particles catalyst for CO 

conversion by applying a nano-fabricated 

screening chip which enables simultaneous 

testing of a chains of supported Pt catalysts of 

controlled particle dimension at different CO 

and O2 pressures. 

MATERIALS AND METHODS  

 

Creation of platinum nanoparticles catalysts 

A combinatorial technique centred on a high 

throughput physical vapour deposition (HT-

PVD) developed by Brian et al. (Hayden et al., 

2009) was used to create thin films of TiO2 and 

TiO2 supported Pt nanoparticles catalyst, Figure 

1.  

 



East Afr. J. Biophys. Comput. Sci. (2022), Vol. 3, No. 2, 11-24 
 

14 

 

Figure 1: Schematic diagram of HT-PVD system indicating two cryo-pumped thin film synthesis 

chambers A and B, sputtering and surface analysis chambers and the load lock (adapted from 

Hannah, 2012). 

This technique creates thin films through 

condensation of evaporated material onto a 

substrate. The deposition chamber consisted of 

three electron gun (e-gun) evaporation sources 

(Temescal) and three Knudsen cell (K-cell) 

sources (DCA). The HT-PVD system 

operational base pressure was 1 x 10-10 mbar. In 

the present study, electron beam sources, E-gun 

1 was applied to evaporate Ti, Pt was 

evaporated from E-gun 3. Titania layers of 

about 200 nm were deposited onto a catalyst 

screening chip from titanium (99.995 %, Alfa 

Aesar metals) from E-gun 1 and oxygen (Air 

products, special gases, 99.999 %) at a constant 

pressure of 9.7 x 10-6 Torr at 1 sccm oxygen 

flow rate and plasma source, Prf = 300 W at a 

deposition rate of 4 Å/s with substrate retained 

at ambient temperature throughout film creation.  

The widths of titania layer deposits were 

managed through depsition time and sample 

thickness was subsequently achieved via 

calibration of deposition rates from AFM 

readings. The AFM (Vecco Autoprobe M5) 

instrument was applied in a contact mode with a 

silicon cantilever, resonance frequency of 180 

kHz, spring constant of 5Nm-1 with an estimate 

tip (CSC17 probe, MikroMasch) curvature of 10 

nm. 

Characterization of platinum nanoparticles 

Characterization and distribution of particle 

dimension was conducted by using TEM where 

a small layer of TiO2, l5-25 nm thick, was 

created onto small carbn cated copper TEM 

grids (Agar scientific). The grids bared TiO2 

produced under the same deposition conditions 

as a catalyst screening chip. Platinum particles 



East Afr. J. Biophys. Comput. Sci. (2022), Vol. 3, No. 2, 11-24 
 

15 

from Pt source (E-gun 3), were created onto a 

screening chip where TiO2 support material was 

previously created through HT-PVD technique. 

The deposition rate of 4 Å/s were achieved by 

creating several thick layers from short to 

extended times, showing that the thickness as 

established on contact masked samples using 

AFM was relative to the depsition duration. 

The rate of Pt deposition (0.15 Å/s) was 

established through creation of continuous Pt 

small films, and reduced deposition durations 

(30 s – 360 s) applied to create Pt particles via 

nucleation and growth on titania substrates at 

250 ℃. For surface characterization of Pt 

nanoparticles on titania substrate, Pt 

nanoparticles were grown onto Formvar® 

carbon coated copper grids (Agar scientific) 

coated with a small layer of titania 15-25 nm 

thick for transmission electron microscope 

(TEM) measurements. Characterization of 

particles was conducted by TEM prior 

deposition onto the screening chip for assurance 

of particles creation. Using Jeol 3010 

instrument, TEM images were attained at an 

accelerating voltage of 300 kV containing a 

Gatan CCD camera for capturing images. X-ray 

Photoectron Spectroscope (XPS) studies were 

conducted in Ultra High Vacuum (UHV) system 

containing a twin anode X-ray source (Mg Kα 

and Al Kα) and a VG Clam Single Channel XPS 

system analyser. Depositions the substances 

were undertaken onto silicon nitride on silicon 

and on a 10 x 10 or 12 x 12 array nano-

fabricated catalyst screening chip (450 µm 

silicon wafer thickness) on which a low pressure 

chemical vapour created (LP-CVD) silicon 

nitride membrane (300 nm and 600 nm) has 

been previously created. The screening chip was 

back etched to create individual membranes. 

The HT-PVD system was set up on a “wedge” 

deposition to generate different particle 

dimensions distributions throughout the support. 

A silicon chip with the dimension of 35 mm x 

35 mm was fabricated (450 mm thick silicon 

wafer) for IR thermography readings and an 

array of 10 x 10 silicon nitride membranes (1.5 

mm x 1.5 mm) of 600 nm thickness were 

produced by back etching of silicon to a layer of 

LP-CVD silicon nitride as described earlier 

(Emmanuel, 2022). The membrane with 200 nm 

of titania substrate was optically transparent. 

For temperature measurement of the membrane, 

a small graphitic carbn layer (ca. 200 nm) was 

created on the back of the membrane supplying 

an emissivity approximate to that of a black 

body. Thin SiN membrane offered a supprt for 

the catalyst with small thermal mass and less 

thermal cnductivity to the surrounding silicn 

chip thus, heat produced in the course of a 

reaction on the catalyst could subsequently 

increase membrane temperature. 

Testing of platinum nanoparticles for 

catalytic activity 

A screening chip with a catalyst created on the 

whole chip was placed on a heated sample 

holder with a heat shield to enable the whole 

chip to be heated evenly up to 250 oC. The 

sample holder was placed in a UHV system an 

IR transparent window (CaF2) and the surface of 

the chip was captured (50 mm focal length 

camera lens) by a thermal camera (Jade III, 

CEDIP) operating in the spectral range of 3.6 – 

5.1 µm with a thermal sensitivity of 20 mK. 

Spatial resolution was 320 x 240 pixels and the 

whole 12 x 12 array was imaged to fill the 

detector. Reactions were conducted in a 

turbomolecular pumped UHV system with a 



East Afr. J. Biophys. Comput. Sci. (2022), Vol. 3, No. 2, 11-24 
 

16 

base pressure of 1 x 10-10 mbar and the 

temperature response of the catalyst on the 

membrane for a given power input (from an 

exothermic reaction) was established via finite 

element thermal modelling (Comsol 

Multiphisics®) (Emmanuel, 2022).  

It is hypothesized that energy loss from the 

membrane primarily occurs via thermal 

conduction through the membrane itself, 

including the titania support and graphite layer, 

to the underlying silicon chip. Radiative and 

convective losses were estimated to be zero 

therefore, extra radiative and convective wastes 

over a few degrees temperature over the base 

temperature of reaction were expected to be 

very minimal (Emmanuel, 2022). For CO 

conversion reaction (∆H = -283 kJmol-1) 

(Emmanuel, 2022) and a pressure of 1 x 10-3 

mbar, assuming each molecule is converted, the 

theoretical power was 2.289 x 10-4 Js-1 mm-2 

(Emmanuel, 2022). This resulted in a calculated 

temperature increase of 4 °C (ΔT = 4 °C) at the 

center of the membrane. The chip's calculated 

sensitivity enabled the determination of the 

reaction turnover frequency (TOF) at the 

catalyst surface. However, the uncertainty in the 

thermal conductivity values of the membrane's 

composite layer led to an estimated error of 

approximately ±30% in the absolute TOF 

values. A detailed simulation of the temperature 

distribution across the 1.5 mm x 1.5 mm 

membrane was previously reported (Emmanuel, 

2022). 

 

 

RESULTS AND DISCUSSION 

Images of TEM for Pt catalyst supported on 

titania resemble those reported earlier in terms 

of their shape and growth mode (Emmanuel, 

2022), Figure 2. The TEM images facilitated the 

determination of particle dimension reliance of 

supported Pt in relative to the equivalent 

coverage of Pt created. On the Figure, particles 

of Pt appear in black relative to the white 

substrate background. At a shorter deposition 

period (30 seconds) in (a), particles are smaller 

(black). Conversely, when deposition periods 

escalate, particles increase in dimension because 

extra Pt is being added as witnessed in the 

dimension of particles in (b), (c) and (d), 

respectively, with deposition periods of 30 

seconds, 2, 3.5 and 5 minutes, respectively.  

In order to establish the change of particle 

dimension distribution after CO conversion 

because it was not possible to have it established 

directly on the chip by TEM, XPS 

measurements were conducted prior and after 

the reaction. A small change  to higher binding 

energy was observed which was associated with 

final-state effect, consistent with earlier studies 

(Liu et al., 2014). The raise in the intensity was 

detected with increasing particle dimension, 

showing that Pt particles were growing in size 

as extra Pt was deposited. The study of Pt core 

level energies show a small but recognizable 

shift in binding energy. 

Studies indicate that the binding energy shifts 

governed by the species to which an atom is 

attached and the binding energies shifts for core 

level electrons can emerge from initial-state or 

final-state effects (Attard and Barnes, 1998, 

Kolasinski:, 2002). 



East Afr. J. Biophys. Comput. Sci. (2022), Vol. 3, No. 2, 11-24 
 

17 

  

 
 

Figure 2: Images of TEM for Pt particles at different deposition periods, (a) 30 seconds, (b) 2 

minutes, (c) 3.5 minutes and (d) 5 minutes with a mean particle dimension of (a) 1.6 nm, (b) 2.6 

nm, (c) 4.9 nm and (d) 6.7 nm 

 

Initial-state effects (chemical shift) are 

attributed to chemical bonding which largely 

affects electronic configuration of an atom 

leading into a large shift in binding energy of up 

to 10 eV (Emmanuel, 2022). Thus, atoms in a 

high oxidation state generate XPS peaks at high 

binding energy as compared to similar atom in a 

low oxidation state (Emmanuel, 2022).  

However, the final-state effects are because of 

the ejection of an electron from an atom which 

a b 

c d 



East Afr. J. Biophys. Comput. Sci. (2022), Vol. 3, No. 2, 11-24 
 

18 

corresponds to an ionic state producing a hole in 

place of the removed photoelectron (Emmanuel, 

2022). Effect of the binding energy shift due to 

final-state is often a slight binding energy shift 

compared to that of initial-state effect. Because 

the core level binding energy shift for Pt 

particles detected in the current study is smaller, 

typically less than 1 eV, it can be linked with 

final state-effect, consistent with the earlier 

reports (Zhang et al., 1997; Guerin et al., 2006; 

Liu et al., 2014,). Figure 3 show the reliance of 

Pt 4f7/2 binding energy for Pt particle dimension 

recorded on the screening chip prior and after 

the reaction on Pt supported catalysts. 

 

 

Figure 3: Binding energy of Pt particle size for the Pt 4f7/2 prior and after the catalytic reaction.  

At a base temperature of 170 oC on Pt catalyst, a 

pressure of a gaseous mixture was 7.2 x l0-2, 8.4 

x 10-2 and 1.04 x 10-1 mbar with O2: CO ratio of 

1:1. For a pre-exposed O2 catalyst surface, the 

pressure was 1.5 x l0-1, 1.9 x l0-1 and 2.2 x 10-1 

mbar with O2: CO ratio of 2:1, 1:1 and 1:1, 

respectively, while on a pre-exposed CO 

catalyst surface the pressure was 1.5 x 10-1, 1.7 

x 10-1 and 2.2 x 10-1 mbar with O2: CO ratio of 

1:2, 1:1 and 1:1, respectively. Besides at 240 ℃ 

and O2: CO ratio of 1:1, the pressure was 6 x 10-

1, 1.1 and 2.4 mbar. 

The temperature was determined concurrently 

n the catalysts integrating ver a 5 minutes 

interval. Catalysts were created such that 

particles dimension was constant throughout the 

rows and differed in the columns of the 

screening chip. The variation in temperature 



East Afr. J. Biophys. Comput. Sci. (2022), Vol. 3, No. 2, 11-24 
 

19 

across a row of similar particle dimensions was 

0.2 ℃, far less than that in the columns and was 

attributed to a partial shielding of the gas flux at 

the boundaries of the sample by the holder. The 

increase, ∆T, in average was applied to establish 

the oxidation rate of CO to CO2 at the catalyst 

assuming the enthalpy of reaction was ∆H = -

283 kJ mol-1 (Emmanuel, 2022). The mass of Pt 

and number of Pt atoms at the surface of the 

particles per catalyst area of catalyst was 

computed from TEM images, assuming the 

particles were hemispherical (Hayden et al., 

2009, Emmanuel, 2022). This allowed the 

computation of TOF at Pt surface. Figure 4 

presents the TOF for CO conversion reaction at 

170 ℃ with the pressure of 7.2 x l0-2, 8.4 x l0-2 

and 1.04 x l0-1 mbar and O2: CO ratio of 1:1. 

 

 

Figure 4: TOF for CO conversion on Pt particles at a pressure of 7.2 x 10-2 (blue triangles), 8.4 x 

10-2 (red circles) and 1.04 x 10-1 mbar (black squires) with O2: CO ratio of 1:1 at 170 ℃.  

In Figure 5 is the TOF for CO conversion 

reaction on a pre-exposed O2 catalyst surface 

with a pressure of 1.5 x 10-1, 1.9 x 10-1 and 2.2 x 

10-1 mbar at O2: CO ratio of 2:1, 1:1 and 1:1, 

respectively, at 170 ℃. Figure 6 presents the 

TOF for CO conversion at 170 ℃ on a pre-

exposed CO catalyst surface with a pressure of 

1.5 x 10-1, 1.7 x 10-1 and 2.2 x 10-1 mbar at O2: 

CO ratio of 1:2, 1:1 and 1:1, respectively 

 



East Afr. J. Biophys. Comput. Sci. (2022), Vol. 3, No. 2, 11-24 
 

20 

 

Figure 5: TOF for CO conversion reaction on Pt particles catalyst for a pre-exposed O2 Pt surface, 

pressure of 1.5 x 10-1 (blue triangles), 1.9 x 10-1 (red circles) and 2.2 x 10-1 mbar (black squires) at 

O2: CO ratio of 2:1, 1:1 and 1:1, respectively, at 170 ℃.  

 

Figure 6: TOF for CO conversion on Pt particles catalyst for a pre-exposed CO Pt surface, 

pressure of 1.5 x 10-1 (blue triangles), 1.7 x 10-1 (red circles) and 2.2 x 10-1 mbar (black squires) at 

O2: CO ratio of 1:2, 1:1 and 1:1, respectively, at 170 ℃.  

 

 



East Afr. J. Biophys. Comput. Sci. (2022), Vol. 3, No. 2, 11-24 
 

21 

The TOF for CO conversion reaction at 240 ℃ 

with a pressure of 6 x 10-1, 1.1 and 2.4 mbar at 

O2: CO ratio of 1:1 is also presented, Figure 7. 

 

 

Figure 7: TOF for CO conversion on Pt particles catalyst at 240 ℃ and O2: CO ratio of 1:1, 

pressure of 6.1 x 10-1 (blue triangles), 1.1 (red circles) and 2.4 mbar (black squires). 

At each temperature, there is an increase in TOF 

as reactants pressures increase revealing that Pt 

catalyst is more active for CO conversion at 

higher pressure. For a pre-exposed O2 catalyst 

surface at 170 ℃, a similar trend in TOF of Pt 

catalyst was observed by increasing pressure, 

Figure 5. The same behaviour in TOF was 

noticed for a pre-exposed CO Pt catalyst surface 

at 170 ℃, Figure 6. Again, reactants pressure 

led to a significant increase in activity of Pt 

catalyst for CO conversion with increasing 

pressure at 240 ℃ as shown by the values of 

TOF in Figure 7. Thus, the highest TOFs of Pt 

particles catalyst were achieved with increasing 

reactants pressure at higher temperature. 

Therefore, at each temperature, there is a linear 

relationship between the TOFs and pressure for 

CO conversion on Pt catalyst. The activity trend 

achieved in the current study is  consistent with 

earlier findings which addressed the dependence 

on O2 and CO pressure of the reaction rate for 

CO conversion on Pt catalysts (Li et al., 2013, 

Berlowitz et al., 1998). For a pre-adsorbed O2 

surface, TOF increased by raising CO pressure 

at O2: CO ratio of 1:1, pressure of 2.2 x 10-1 

mbar and on a Pt surface pre-adsorbed with CO, 

a similar trend was achieved, consistent with 

earlier reports (Berlowitz et al., 1998; Johanek 

et al., 2004; Li et al., 2013). TOF of Pt catalyst 

at 240 ℃ and higher reactant pressures resulted 

in the highest TOFs although a slight decline in 

activity was observed at 2.4 mbar, Figure 7. For 

example, TOF declined from 4.355 s-1 at 1.1 

mbar to 4.174 s-1 at 2.4 mbar on Pt particle 

dimension of 1.3 nm. The fall of activity is 

attributed to CO inhibition of Pt catalyst surface 



East Afr. J. Biophys. Comput. Sci. (2022), Vol. 3, No. 2, 11-24 
 

22 

prohibiting O2 adsorption and breakage on the 

catalyst surface, an important reaction pathway 

thus, decreasing Pt activity, in agreement with 

previous findings (McClure and Goodman, 

2009). Results show that CO conversion on Pt 

catalyst is influenced by reactants pressure and 

surface temperature (Kolasinski:, 2002).  For 

instance, at 170 ℃ and O2: CO ratio of 1:1, 

Figure 4, TOF raised from 0.259 s-1 at 7.2 x 10-2 

mbar to 1.991 s-1 at 1.04 x 10-1 mbar on Pt 

particle dimension of 1.3 nm. A similar raise in 

activity with increasing reactants pressure was 

attained on a pre-adsorbed O2 Pt catalyst surface 

where TOF increased from 0.671 s-1 at 1.5 x 10-

1 mbar to 1.889 s-1 at 2.2 x 10-1 mbar on Pt 

particle dimension of 1.3 nm, Figure 5. Besides, 

TOF increased from 0.946 s-1 at 1.5 x 10-1 mbar 

to 1.903 s-1 at 2.2 x 10-1 mbar on Pt particle 

dimension of 1.3 nm for a pre-adsorbed CO Pt 

surface, Figure 6. However, a competitive 

adsorption exists among CO and O2 towards Pt 

surface, though CO can adsorb on an O2 

occupied surface, O2 cannot adsorb on a CO 

occupied surface. Therefore, at high CO 

occupied surface, the reaction is restricted by O2 

thus, raising CO pressure prevents the reaction 

because there are no extra adsorption sites for 

O2. Contrary, at low CO occupied surface, 

oxygen adsorption occurs rapidly and the 

reaction relies on the surface coverage of CO 

and O2 (Kolasinski:, 2002). Usually, higher CO 

conversion to CO2 is attained at situations that 

allow least CO surface occupancy (McClure and 

Goodman, 2009). In addition to temperature and 

pressure, CO conversion on Pt is dependent on 

particles dimension where the smallest particles 

exhibit higher activity. Although there is no 

common agreement from literature about the 

influence of particle dimension for supported Pt 

catalyst, results show that Pt particles within 1.1 

nm and 10 nm, for CO conversion at different 

temperatures the activity increases with 

decreasing particle dimensions (Li et al., 2013). 

This is because for particle dimension of lower 

than 10 nm, the comparative number of kink 

sites, steps and corners raises monotonically 

with declining dimension and the low-

coordinated surface atoms bare huge difference 

in the capability to react with molecules from 

the gas phase thus, accelerating the reaction 

(Overbury et al., 2006; Li et al., 2013). 

However, it is necessary to relate the activity 

trend with pressure at 170 ℃ and that attained at 

240 ℃. Results show higher activity of Pt 

catalyst at 240 ℃ as reflected in TOF with 

increasing pressure, for instance, TOF increased 

from 3.312 s-1 at 6.1 x 10-1 mbar to 4.355 s-1 at 

1.1 mbar on Pt particle dimension of 1.3 nm. 

Studies show that Pt surface is exceptionally 

active at high reactant gas pressure and 

temperature because at low temperatures, the 

CO repressed regime takes over and the reaction 

is prohibited by adsorbed CO which preventing 

adsorption and breakage of O2 thus, leading to 

low catalytic activity of Pt catalyst (Gao et al., 

2009, McClure and Goodman, 2009, Liu et al., 

2010). However, at all pressure and temperature 

conditions investigated in the current study, CO 

conversion rate increased with increasing 

pressure. Such activity trend illustrates the 

influence of pressure and temperature for CO 

conversion on Pt nanoparticles catalyst in 

addition to Pt particles dimension. This 

behaviour is consistent with earlier findings on 

the reliance of pressure of O2 and CO of the 

reaction rate for CO conversion on a similar 

system (Berlowitz et al., 1998; Li et al., 2013). 

These result can be considered in the light of the 

influence of pressure to explain high activity of 

Pt catalyst at high pressure and temperature 



East Afr. J. Biophys. Comput. Sci. (2022), Vol. 3, No. 2, 11-24 
 

23 

among other factors (Li et al., 2013). The 

findings indicate that at a particular temperature, 

an increase of pressure yields the highest 

activity compared to that obtained at low 

pressure and temperature. Thus, these results 

provide the evidence of the influence of 

pressure on CO conversion on Pt particles 

catalyst at a given reaction temperature.  

CONCLUSION 

The CO conversion on titania supported Pt 

catalyst of different particle dimension between 

1.3 nm and 7.8 nm at different reactants 

pressures was measured simultaneously on 120 

catalysts at 170 and 240 ℃ and at different 

reactants pressures. The XPS studies indicated a 

small change of particle dimension after the 

reaction. At each temperature studied, a linear 

relationship between TOF for CO conversion on 

Pt catalyst and pressure was attained. However, 

the highest TOF for CO conversion on Pt was 

observed at higher pressure and temperature of 

240 ℃, consistent with earlier findings on 

similar catalyst system (Li et al., 2013, 

Berlowitz et al., 1998). However, a slight 

decline in activity was observed with a pressure 

of 2.4 mbar at 240 ℃ which is attributed to CO 

poisoning of Pt catalyst, consistence with earlier 

findings (McClure and Goodman, 2009). 

Besides, the smallest Pt particles attained the 

higher TOFs, in agreement with earlier reports. 

Acknowledgement 

The author honorably appreciates the significant 

contribution, advise, guidance, encouragement 

and supervision roles from Professor Brian 

Hayden. The author also acknowledges the 

financial support from the employer, Mkwawa 

University College of Education. 

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