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The catalytic activity of two catalysts on the production of hydrogen by steam reforming of bio-oil is compared on a laboratory scale fix-bed reactor. A series of composite catalysts Ni/CeO2-ZrO2Â were prepared via impregnation method with Ni as the active metal. A laboratory-scale fixed-bed reactor was employed to investigate the catalyst performance duringÂ hydrogenÂ productionÂ byÂ steam reformingÂ bio-oil aqueous fraction. Effects of water-to-bio-oil ratio (W/B), reaction temperature, and the loaded weight of Ni and Ce on the hydrogenÂ productionÂ performance of Ni/CeO2-ZrO2Â catalysts were examined. The obtained results were then compared with commercial nickel-based catalysts (Z417).
Keywords:Â Ni/CeO2-ZrO2;Â Hydrogen; Bio-oil;Â Steam reforming
Aim of the paper:-
To effectively critique the paper on the methodology used, experimental results and discuss on the overall technical details of the paper.
Then objective of the critiqued paper is to analyse the performance of two catalysts, Ni/CeO2-ZrO2 self prepared and commercial nickel based catalyst (Z417) in the hydrogen production process from bio-oil in steam reformation method. A laboratory scale fixed bed reactor is used to investigate the self prepared catalysts performance during hydrogen production and with the obtained results the self prepared catalyst (Ni/CeO2-ZrO2) performance is compared with the commercially available catalyst (Z417).
Fossil fuels which meet the energy demands of the world are depleting fast today. Also, the environmental impacts during the production of energy from fossil fuels by combustion are causing global warming. Therefore a lot of technical and scientific research has to be carried out to replace the fossil fuels. Hydrogen which is available in abundance is one such alternative for the fossil fuel. But hydrogen (H2) as such is not found in the earth naturally, it is found only in compound form with other elements. Hydrogen generally bonds with carbon and forms different compound such as methane, coal, petroleum and most importantly in biomass plants.
The amount of energy produced during hydrogen combustion is higher than released by any other fuel on a mass basis, with a lower heating value of 2.4, 2.8 and 4 times higher than that of methane, gasoline and coal. Different sources to produce hydrogen are shown in fig 1.
Figure Hydrogen sources
Production of hydrogen from biomass plants has attracted considerable attention because it is not only environment friendly but also an environmentally friendly resource. Biomass is the fourth largest source of energy in the world and has the potential to accelerate the realisation of hydrogen as a major fuel. The yield of hydrogen is low from biomass as the hydrogen content in biomass is low i.e., (approximately 6% versus 25% methane) and the energy content is low due to the 40% of oxygen content in biomass. .
Hydrogen production from biomass is done by two methods 
Thermo-Chemical process involving pyrolysis, conventional gasification, super critical gasification (SCWG).
Biological Conversions involving fermentative hydrogen production, photosynthesis, biological water gas shift reaction (BWGS).
Pyrolysis is the conversion of biomass liquid, solid and gas by heating the biomass in the absence of air at around 500 Í¦C. It also produces in addition to gas a product called as bio-oil which is the basis of several processes for the development of various energy fuels and chemicals. The process is an endothermic reaction process.
In the conventional gasification process, biomass is heated at high temperatures and disengaged to combustible gas. Air, steam or oxygen is used as a gasification agent to increase the energy value.
In the third method water is miscible (mixed to form homogeneous solution) with organic substance above the critical point (temperatures >374 Í¦C, pressure >22MPa). This method is more effective method to produce hydrogen thermo-chemically.
Biological conversion method
In the fermentative method, hydrogen is produced by anaerobic organisms (dark fermentation) and photo fermentation (light fermentation) using carbohydrate rich biomass as a renewable energy source. First, the highly concentrated solution of the biomass is fermented by anaerobic organisms to produce fatty acids, hydrogen and CO2. The produced acids are further fermented to produce photo-heterotrophicÂ bacteria to produce CO2 and H2.
In the photosynthesis method, many phototropic organisms likeÂ purple bacteria, greenÂ bacteria,Â CyanobacteriaÂ and severalÂ algae are used to produce hydrogen by photosynthesis process.
In the BWGS method, Rubrivivax gelatinosus (photo-heterotrophic bacteria) is used to produce hydrogen. This bacteria is capable of performing water gas shift reaction at ambient temperature and atmospheric pressure. During this gas shift reaction process, it converts 100% CO into near stoichiometric amount of hydrogen.
Background / Critical literature survey
In this paper, the performance of a self prepared catalyst is compared with a commercially available catalyst. A catalyst is a chemical substance that affects the rate of a chemical reaction by altering the activation energy required for the reaction to proceed. This is called as catalysis. A catalyst is not consumed by the reaction and it may participate in multiple reactions at a time. The only difference between a catalyzed and an uncatalyzed reaction is that the activation energy is different. . There are two types of catalysts. They are positive and negative catalyst. The catalyst that speeds up the reaction is a positive catalyst and the one which slows the reaction is called as the negative catalyst. The following are the criteria for a good catalyst. They are
The principal factors in catalysis and how they are interrelated is shown in the figure 2.
Figure Principle Factors in Catalysis
The figure 2 shows the desirable and undesirable reactions in the overall process as well as the fundamental properties and their mutual relationships in the different steps leads to the choice of the active species.
The catalysts preparation methods are
The main pathways and objectives of in the preparation of unsupported catalysts, including both high-temperature and solution methods is shown in the figure3. In the figure 3, the dashed line seperates the high-temperature (A) and solution methods (B).
Figure Production of unsupported catalysts
In this paper the catalyst preparation method is done by precipitation/impregnation method.
Precipitation is one of the most widely used preparation methods and may be used to prepare either single component catalysts and support or mixed catalysts. The precipitation of a crystaline can be divided into three steps. They are,
In supersaturation step, the system is unstable and precipitation occurs as a result of any small perturbation. Supersaturation is reached by means of physical transformations or chemical process. Several parameters influence the quality of the final precipitates and fine tuning of the parameters is necessary in order to produce the required material. This is shown in the figure 4.
The impregnation method involves three steps.
Contacting the support with the impregnating solution for a certain period of time
Drying the support to remove the imbibed liquid and
Activating the catalyst by calcination, reduction or other appropriate treatment.
Two method of contacting may be distinguished depending on the total amount of solution. In the first method with excess of solution the support is placed on a screen and dipped into an excess quantity of solution for the time necessary for total impregnation.
Figure Factors affecting the main properties of the precipitated catalysts
The solid is then drained and dried. With repeated application of solution in the second method, a more precise control is achieved by this technique, termed dry impregnation or impregnation to incipient wetness. The support is contacted with a solution of appropriate concentration, corresponding in quantity to the total known pore volume. For both the methods the operating variable is the temperature which affects both the precursor solubility and the solution viscosity and as a consequence the wetting time.
Figure Impregnation methods with excess of solution 
Figure Impregnation to incipient wetness 
Steam reforming technologies for a typical layout of a hydrogen plant based on steam reforming includes the following steps. .
First is the feedstock treatment where sulphur and other contaminants are removed.
The second is the steam methane reformer, which converts feedstock and steam to syngas (hydrogen and carbon monoxide) at high temperature and moderate pressure. In case of multiple or heavy feeds and for large capacities, an adiabatic, catalytic pre-reforming step is foreseen upstream the SMR
The third section is the syngas heat recovery and incorporates CO shift reactor to increase the hydrogen yield
The final section is the raw hydrogen purification, in which modern plants employ a pressure swing adsorption (PSA) unit to achieve the final product.
Figure Steam reformation in a hydrogen plant
The reforming reaction between steam and hydrocarbons is highly endothermic and is carried out using specially formulated nickel catalyst contained in vertical tubes situated in the radiant section of the reformer. The simplified chemical reactions are: 
CnH2n + 2+ nH2O = nCO + (2n+1)H2 (for saturated hydrocarbons)
CH4 + H2O = CO + 3H2
In the adiabatic CO shift reactor vessel, the moderately exothermic water gas shift reaction converts CO and steam to CO2 and H.
CO + H2O = CO2 + H2
The PSA purification unit removes hydrogen by adsorption. SMR is a mature technology and is now less likely to yield any large step changes in economic benefit from technological developments.
Topsoe's latest development in the steam reforming process is the advanced technology in the steam reforming process. The characteristic of this process are
High reformer outlet temperature
Low steam to carbon ratio
High combustion air preheat
High heat flux reformer
Low steam to carbon ration, typically 2.5, in hydrogen plants reduces the mass flow through the plant and thus the size of equipment. The lowest investment is obtained for low steam to carbon ratios; however, it increases the methane leakage from the reformer. This is compensated by increasing the reformer outlet temperature to typically 1690 Í¦F in hydrogen plants. Also at low ratio operating states requires the use of non-iron containing catalyst i.e., a copper based medium temperature shift to eliminate the production of by-products in the shift section.
Balat M, Balat M  & Kalinci Y, Hepbasli A, Dincer I  discusses the political, economic and environmental impacts of the producing hydrogen from biomass. Both the papers discuss on the how hydrogen is a promising renewable fuel for transportation and domestic applications. It also enlightens the political and the environmental impacts and its benefits during the usage of hydrogen to reduce carbon.
Schoeters J et al  described the fluidized-bed gasification of biomass using an experimental study done on a bench scale reactor carried out in the Department of Chemical Engineering and Industrial Chemistry projects under taken by several governmental and non-governmental organisations in Brussels, Belgium.
Cohce MK et al  discussed on thermodynamic analysis of hydrogen production from biomass gasification. In this paper, Batelle Columbus Laboratory setup simulation is used to investigate the thermodynamic performance of the gasification process followed by the steam methane reforming (SMR) and shift reactions for producing hydrogen from palm oil shell.
Lappas et al  & Baumlin et al  & Zhang Q et al  have discussed hydrogen production is by steam reforming of the pyrolysis oil or bio-oil. Pyrolysis oil or bio-oil is a mixture of acids, aldehydes, esters, ketones, sugars, phenols, guaiacols, syringols, furans . Conversion of bio-oil to biomass in large scale improves the development of biomass energy utilisation . But during the conversion process the entire bio-oil tends to polymerise, clogging the feedstock inlet because of its complex composition. With the addition of water, the bio-oil is separated into hydro-phobic lignin and aqueous (hydrophilic) components. The hydrophilic components are steam reformed to produce hydrogen while the hydrophobic lignin is used to generate different chemicals and additives. This method is cost-effective and it is free from feeding problems. ,[ 11].
Steam reforming of bio-oil can be described by the following reaction stoichiometry
Cn Hm Ok + (n-k) H2O -> nCO + (n+m/2-k)H2
The above reaction is followed by the water gas shift (WGS) reaction.
CO + H2O -> CO2 + H2
Therefore the overall process of the bio-oil steam reformation is expressed as
Cn Hm Ok + (2n-k) H2O -> nCO + (2n+m/2-k) H2
A side effect of the above reactions is the coking of industrial catalytic process. Coking or the formation of carbonaceous deposits is an important one in the catalyst development. This is discussed briefly in the  and  papers.
Chornet et al [14-20] investigated the process of steam reforming of bio-oil aqueos fraction and proposed an integrated process concept of hydrogen production through the bio-oil aqueous fraction.
Basagiannis et al [15 - 17] investigated the influence of the noble metals and nickel and their support type (Al2O3, La2O3/Al2O3, MgO/Al2O3) on bio-oil reforming. In this paper, acetic acid, one of the major components of bio-oil is reaction network under steam reforming conditions is studied for Al2O3 & La2O3 and Ni catalyst supported on La2O3/ Al2O3 carrier for both transient and steady state techniques.
Takanabe et al [21-25], have conducted a lot of studies on the steam reforming of the model compound of bio-oil. They also investigated steam reforming of acetic acid over Pt/ZrO2 catalysts.
Aupretre F et al [25-28] discusses the catalytic behaviour of silica- supported metals, bio-ethanol catalytic steam reforming over supported metal catalysts, catalytic hydrogenolysis of ethane over noble metals.
Comas J et al [29 -30] discuss the bio-ethanol steam reforming on Ni/Al2O3 catalyst and the improvement of the steam reforming process by addition of Zirconia in the Ni/Al2O3 catalyst.
Matsumra Y et al  discusses the steam reforming of methane over nickel catalysts at low reaction temperatures. In this paper, the effects of supports such as silica, alumina and zicrona for nickel catalysts have been studied in steam reforming of methane at 500 Í¦C. It is observed that the activity of nickel supported on silica reduced with hydrogen at 500 Í¦C decreases with oxidation of nickel particles during the reaction.
Zhang BC et al , investigated ceria supported CO, Ir and Ni catalysts for steam reforming of ethanol in the temperature range of 300 Í¦C to 700 Í¦ C with respect to the nature of the active metals and the catalytic stability. They discussed for both low temperature and high temperature effect of the catalyst.
www.osti.gov website is the office of scientific & Technical information is a U.S. Department of energy (DOE) program within the office of science, is a supporter of basic research in the physical sciences in the United States. The main objective of OSTI is to advance science and sustain technological creativity by making R&D findings available and useful to DOE research. This website provides the necessary technical information for the hydrogen production and their different sources.
www.chemistry.about.com gives the necessary details about the basic reactions and the basic chemistry about catalysts and its role in a chemical reaction.
In this paper a series of Ni/CeO2/ZrO2 catalysts are prepared and it has been applied to the steam reforming reaction of the real bio-oil that was obtained from rice hull by fast pyrolysis. The main objective of the paper is then to compare the results with a commercially prepared catalyst Z417 with the self prepared catalyst.
The experimental setup is done in a two stage process. First the bio-oil and the catalyst are prepared and then the experiment is carried out in laboratory scale fixed bed reactor system.
Bio-oil and catalyst preparation
The catalyst preparation method plays a major role as it affects the acid-base properties of the catalyst and this affects the activity and product distribution for CO hydrogenation. There are 3 different methods to prepare the ZrO2 catalyst. They are
Here the ZrO2 support catalyst is prepared using the precipitation method. First the aqueous solution of ZrOCl2 is added to a solution of ammonium hydroxide according to the ratio of n(Zr)/n(OH-) at a temperature of 50 Í¦C and pH = 9. The resulting precipitate is filtered and washed with distilled water and then dried in air at 110 Í¦C for 6 hours and finally the support precursor is calcined in air at a temperature of 600 Í¦ C for 6 hours.
Then a series of Ni/CeO2-ZrO2 catalysts with different Ni2+ and Ce4+ concentration were prepared by impregnating ZrO2 powder with Ni(NO3)2 . 6H2Oand Ce(NO3)3 . 6H2O, as Ni and Ce precursor. Then the prepared concentrate is dried at 110 Í¦C for 12 hours. The dried concentrate is then calcinated at 800 Í¦C for 6 hours and by natural cooling for testing.
Bio-oil employed in the experiment was produced from rice hull in an auto-thermal biomass pyrolysis reactor (obtained from Renewable Clean Energy Laboratory, University of Science and Technology of China) . It has a density of 1150 kg/m3, with a heat value of 12.8 x 103 kJ/kg, a pH value of 3.2 and a viscosity of 110mm2/s at room temperature. The fractions were produced by adding water to the bio-oil at a weight ratio of 1-4:1. The bio-oil separates into an aqueous fraction and hydro-phobic fractions. The main elemental compositions of the bio oil, the organics in its aqueous fraction and hydro-phobic fractions are given in Table 1. The figure shows the DTG curve, which was carried out in the temperature range of 40-850 Í¦C with heating rate of 5 Í¦C/min. Weight loss of bio oil mainly takes place during 100-400 Í¦C. Characteristic peaks of bio-oil pyrolysis vapour detected by IR spectrum are shown in fig 9 and their corresponding substance or functional groups are listed in Table 2.
Table Elemental composition of bio-oil
Table Characteristic peaks in IR spectrum for the corresponding substance or functional groups
Functional Group or substance
2361 cm-1, 2342 cm-1
3032 cm-1, 1318 cm-1
2820 cm-1, 2720 cm-1
1420 cm-1, 1285 cm-1
Figure DTG curve of bio-oil in nitrogen atmosphere
Figure Infrared absorbance of bio-oil pyrolysis
Apparatus and steam reforming tests
The figure 10 shows the schematic illustration of the laboratory scale fixed-bed reactor made of quartz under atmospheric pressure. The catalyst powder was placed in the middle of the quartz tube and is heated by the furnace equipment which is equipped with a temperature controller to monitor the temperature. For the purpose of preheating and dispersing the bio-oil aqueous fraction vapour, the porcelain materials were packed above the catalyst bed. The bio-oil aqueous fraction was fed into the system at a constant rate by a peristaltic pump. The gas exiting from the reactor was cooled and dried before entering gas chromatograph for analysis.
The bio-oil fraction steam reforming performance over a self made catalyst was studied by measuring hydrogen yield efficiency and the content of product gas. The hydrogen yield efficiency is denoted as YH2 and the content of product gas is denoted as V% product. The measured value of the nitrogen gas component is normalized as it is introduced as a carrier gas.
Figure Schematic diagram of the laboratary-scale fix-bed reactor system
The hydrogen content defined in the terms of moles of hydrogen in per mole of product gas is
Hydrogen yield is calculated as
Results and discussions
The results are discussed with the obtained data from the experimental setup. From the obtained results graphs are plotted to discuss the effect of various parameters in the hydrogen production.
First the effect of reaction temperature on the bio-oil steam reforming over the self prepared catalyst (Ni/CeO2-ZrO2) is studied in a temperature range 450 Í¦ C to 800 Í¦C. Then its reaction is studied with the effect of Ni loading in the catalyst varied from 5 wt% to 12 wt% and the Ce loading fixed at 10 wt%. After this the effect of Ce loading in the catalyst is studied with Ni fixed at 12 wt% and Ce is varied between 5 wt% and 10 wt % in the catalyst and then the effect of molar water-to-bio-oil ratio is studied on the reforming reaction. Finally with the available experimental results, the effect of both the self prepared catalyst Ni/CeO2-ZrO2 and the commercially available catalyst Z417 is studied.
Effect of reaction temperature
The effects of the reaction temperature on the bio-oil steam reforming over the Ni/CeO2-ZrO2 (12 wt% Ni, 7.5 wt% Ce) catalyst in the temperature range of 450 Í¦C - 800 Í¦ C is shown in the figure11.
Figure Effects of reaction temperature on the hydrogen yield
From the figure 11 we can see that the hydrogen yield has increased with the increase in temperature. In the figure the black line represents the hydrogen yield and the red line represents the hydrogen content in terms of moles of hydrogen in per mole of product gas, the green line is the content of CO, aqua line is the content of carbon dioxide and the blue line is the content of methane. In the figure we can observe that at 450 Í¦C the hydrogen yield is approximately less than 10%. But as the reaction temperature increases, the hydrogen yield also increases and reaches a maximum of about 70% approximately at 800 Í¦ C while the content of CO reduces to less than 10%. Also it is observed that during the temperature increase, the hydrogen content and the carbon dioxide content increases. The very interesting phenomenon observed in the figure 11 is that first the content of carbon dioxide reached a minimum value while CO reached a maximum value at 550 Í¦C. This phenomenon explains the water gas shift reaction and reverse water gas shift reaction in equation. Secondly at 700 Í¦C, the content of methane reaches a maximum value and then it decreases.
Effect of Ni loading
Now the effect of Ni loading is shown in the figure 12 where the catalytic performance for the steam reforming of bio-oil aqueous fraction over the Ni/CeO2-ZrO2 is evaluated in the temperature range of 450-800 Í¦ C. For this study, the Ni loading in the catalyst is varied from 5 wt% to 12 wt% and the Ce loading fixed at 10 wt%. From the figure 12 we can see that the catalysts performed low catalytic activities at temperature below 650 Í¦ C, while the hydrogen yield could be obtained above this temperature. The activities of the catalysts were improved with the increase of Ni loading and also the hydrogen yield increased with the increase in the temperature. From the figure 12 the hydrogen yield reached the maximum when the Ni loading is 12% in the Ni/CeO2-ZrO2 catalyst and the W/B ratio is 4.9.
Figure Effects of Ni content on the Hydrogen yield
Figure Effects of Ni content on the product gas
The figure 13 also depicts that the Ni content in the yield of Co, methane and carbon dioxide.
Effect of Ce loading
In this step the Ni loading is kept constant at 12 wt% and the Ce loading is varied from 5 wt% to 10 wt% in the catalyst. The catalytic performance of the catalysts for the steam reforming of bio-oil aqueous fraction were evaluated in the temperature range of 450 to 800 Í¦C.
Figure Effects of Ce content on the hydrogen yield
In the figure 14, the black line represents the hydrogen yield when the Ce loading is 10 wt% and the red at 7.5 wt% and the green at 5 wt%. From the figure we can observe that as the temperature increases the hydrogen yield increases. Also the hydrogen yield increases as the Ce concentration is increased from 5 wt% to 7.5 wt% above which the hydrogen yield started to decrease.
Figure Effects of the Ce content on the hydrogen yield
The figure 15 depicts the effect of Ce on the hydrogen yield. The loading of CeO2 could improve the stability of the Ni based catalysts because CeO2 has high oxygen storing and releasing capacity. This will lead to better anti-carbon deposition ability of catalysts. Thus the loading CeO2 plays an important role on the activity of the Ni/CeO2-ZrO2 catalyst.
Effect of molar-water-to-bio-oil ratio
Figure 16 presents the effects of the W/B ratio on the reforming reaction. The hydrogen yield and the content of the product gas are used to depict the W/B ratio range from 3.2 to 5.8. It could be found that W/B ratio has a great effect on the hydrogen yield and the content of the product gas. When the W/B ratio is increased from 3.2 to 4.9% the hydrogen yield increased from 64.7% to 69.7% and when the ratio is further increased to 5.8%, the hydrogen yield decreased to 60.8%. on the other hand, the methane content decreased when the W/B ratio is increased from 3.2 to 4.9 % but when it is further increased to 5.8%, the methane content increased slightly. Also the CO content decreased with the increase in the Carbon dioxide content. This is explained by the WGS reaction. However when the W/B ratio is high it results in the decrease of hydrogen yield because of the adsorption of H2O molecular will occupy the most of the active sites of the catalyst surface, which leads to hydrogen conversion. From the figure 16 it can be concluded that the optimal W/B ratio is 4.9.
Figure Effects of W/B on the hydrogen yield
Comparison of self prepared and commercial catalysts
The figure 17 shows the hydrogen yield affected by the reaction temperature for self prepared Ni/CeO2-ZrO2 catalyst with the concentration of 12 wt% Ni, 7.5 wt% Ce and commercial nickel based catalyst Z417.
Figure Comparison of hydrogen yield between the self prepared and commercially available catalyst
Form the figure 17 it is clearly evident that hydrogen yield of the commercially available catalyst Z417 is less than that of the self prepared catalyst Ni/CeO2-ZrO2.
Table Comparison of the content of the product gas between self made catalyst and commercial catalyst
Commercial Catalyst Z417
Figure Comparison of the catalysts on long term stability
In the fig 17 it is seen that the long term stability of the self prepared catalyst is better than the commercially available catalyst for the bio-oil steam reforming.
From the obtained results we can observe that the self prepared catalyst Ni/CeO2-ZrO2 yields more hydrogen than the commercially available catalyst Z417. This shows that the self prepared catalyst has better catalytic activity than the commercial catalyst. Also the long term stability of the self prepared catalyst is better than the commercially available catalyst.
Critique of the paper:-
In this paper the author has compared two catalysts role in the production of hydrogen; one is self prepared catalyst through precipitation and impregnation method and the other commercially available catalyst. The author has given good reference of how the catalyst is prepared and why that particular method is chosen. In the experimental section the author has clearly explained the experimental setup and the process flow with diagrams and tables. In the results and discussions section the author has given the effect of each metal on the catalyst activity in the production of hydrogen and then compared both the catalyst on hydrogen yield capacity and on terms of long term stability. The data interpretation of the graphs is clear and understandable. Overall the paper is well referenced, the catalyst preparation and the experimental setup is clearly explained with figure and graphs where ever necessary.
The author could have given more details about the commercially available catalyst Z417 and could have also given the experimental results for the effects of the catalyst on the hydrogen production like the self prepared catalyst.
The catalyst preparation method of the self prepared catalyst Ni/CeO2-ZrO2 with the impregnation method with details like the elemental composition of bio-oil is given in detail. Then from the obtained experimental results, self prepared catalysts Ni/CeO2-ZrO2 had better catalytic activity and long term stability when compared with the commercial catalyst Z417 in the production of hydrogen by steam reforming of bio-oil. The effects of Ni loading, Ce loading on the self prepared catalyst were discussed to see the catalytic activity impact on the hydrogen production. Therefore from the experimental results it is clearly evident that self prepared catalyst had better hydrogen yield than the commercially available catalyst.