Riitta L. Keiski

Nitrogen-Doped Anatase Nanofibers Decorated with Noble Metal Nanoparticles for Photocatalytic Production of Hydrogen

We report the synthesis of N-doped TiO(2) nanofibers and high photocatalytic efficiency in generating hydrogen from ethanol-water mixtures under UV-A and UV-B irradiation. Titanate nanofibers synthesized by hydrothermal method are annealed in air and/or ammonia to achieve N-doped anatase fibers. Depending on the synthesis route, either interstitial N atoms or new N-Ti bonds appear in the lattice, resulting in slight lattice expansion as shown by XPS and HR-TEM analysis, respectively. These nanofibers were then used as support for Pd and Pt nanoparticles deposited with wet impregnation followed by calcination and reduction. In the hydrogen generation tests, the N-doped samples were clearly outperforming their undoped counterparts, showing remarkable efficiency not only under UV-B but also with UV-A illumination. When 100 mg of catalyst (N-doped TiO(2) nanofiber decorated with Pt nanoparticles) was applied to 1 L of water-ethanol mixture, the H(2) evolution rates were as high as 700 μmol/h (UV-A) and 2250 μmol/h (UV-B) corresponding to photo energy conversion percentages of ∼3.6 and ∼12.3%, respectively.

Stationary and transient kinetics of the high temperature water-gas shift reaction

The high temperature water-gas shift reaction over an industrial Fe3O4Cr2O3 catalyst was investigated by stationary and transient experiments in isothermal conditions and at elevated pressures. A new modular computer controlled catalyst evaluation unit which can be operated either as a plug flow tubular reactor (PFTR) or a gradientless reactor was used. The plug flow mode was used to produce kinetic data for power-law kinetic models and the gradientless reactor to generate kinetic data for classical kinetic models. Separate chemisorption of CO, CO2, and H2 were done at 293, 373, 473 and 623 or 673 K to study the importance of these components as surface intermediates in the shift reaction. In PFTR the kinetic experiments were performed at 3–5 bar and 573–633 K in two separate series during the slow decay of the catalyst activity. The age of the catalyst in these experimental series was 200–280 and 725–763 h, respectively. The transient experiments were performed in the gradientless reactor at 573–623 K and 5 bar the age of the catalyst being 200–870 h. According to the stationary studies, the reaction rate is strongly dependent on the CO concentration, weakly dependent on the H2O concentration and practically independent on the CO2 and H2 concentrations. The reaction orders with respect to CO and H2O were around 1 and 0.5. In transient experiments CO2 was always liberated faster than H2 when the catalyst pretreatment was done without water. During the pretreatment of the catalyst with H2ON2, small amounts of H2 were formed. The H2O pretreatment retarded the CO2 response. Based on these results a reaction mechanism was proposed which consisted of CO adsorption and oxidation steps as well as of H2O adsorption, decomposition and H2 formation steps. The rate determining steps were the CO oxidation and H2 formation steps. Non-dissociative (CO, CO2) and dissociative (H2) adsorption were described with Langmuir isotherms.

Three-Dimensional Carbon Nanotube Scaffolds as Particulate Filters and Catalyst Support Membranes

Three-dimensional carbon nanotube scaffolds created using micromachined Si/SiO2 templates are used as nanoparticulate filters and support membranes for gas-phase heterogeneous catalysis. The filtering efficiency of better than 99% is shown for the scaffolds in filtering submicrometer particles from air. In the hydrogenation of propene to propane reaction low activation energy of E(a) approximately 27.8 +/- 0.6 kJ x mol(-1), a considerably high turnover rate of approximately 1.1 molecules x Pd site(-1) x s(-1) and durable activity for the reaction are observed with Pd decorated membranes. It is demonstrated that appropriate engineering of macroscopic-ordered nanotube architectures can lead to multifunctional applications.

Removal of aqueous As(III) and As(V) by hydrous titanium dioxide.

Dissolved arsenic in drinking water is a global concern as it causes serious health problems. The purpose of this research was to study the applicability of an industrial intermediate product, a mixture of titanium hydroxide and titanium dioxide for removing aqueous arsenic. The material is common, inexpensive, and non-toxic, making it an attractive choice for drinking water purification. The kinetics and equilibrium of removing both primary inorganic arsenic forms, As(III) and As(V), were studied by separate batch experiments. The tested material functioned well in removing both of these arsenic forms. The apparent values for Langmuir monolayer sorption capacities were 31.8 mg/g for As(III) and 33.4 mg/g for As(V) at pH 4. The studied TiO(2) performed the best in acidic conditions, but also reasonably well in other pH conditions.

Micellar-enhanced ultrafiltration for the removal of cadmium and zinc: use of response surface methodology to improve understanding of process performance and optimisation.

In this study, removal of cadmium and zinc from their respective water samples was conducted by micellar-enhanced ultrafiltration (MEUF), using sodium dodecyl sulfate (SDS) as the surfactant. Response surface methodology (RSM) was used for modelling and optimising the process, and to gain a better understanding of the process performance. Face Centred Composite (CCF) Design was used as the experimental design. The factors studied were pressure (P), nominal molecular weight limit (NMWL), heavy metal feed concentration (C(Zn), C(Cd)) and SDS feed concentration (C(SDS)). Using RSM the retention of heavy metals was maximized while optimising the surfactant to metal ratio (S/M). Response surface plots improved the understanding the effect of the factors on permeate flux. Concentration polarisation was negligible and therefore, high NMWL membranes with high pressure provided high flux with negligible effect on the retention of heavy metals. The optimal conditions of zinc removal were C(SDS)=13.9 mM, C(Zn)=0.5 mM, NMWL=10 kDa and P=3.0 bar, and for cadmium removal C(SDS)=14.2 mM, C(Cd)=0.5 mM, NMWL=10 kDa and P=3.0 bar. The retentions achieved were 98.0+/-0.4% for zinc and 99.0+/-0.4% for cadmium. To improve resource efficiency, the surfactant was reclaimed after use; 84% of the initial SDS was recovered by precipitation.

Water-gas shift reaction on a cobalt-molybdenum oxide catalyst

Abstract The activity of a commercial Co-Mo oxide catalyst in the water-gas shift reaction was studied with transient response experiments in a gradientless spinning basket reactor operating at 350-400 °C and at atmospheric pressure. The Co-Mo oxide catalyzed the shift reaction at temperatures above 350°C, whereas the activity was low at 350 ° C. The transient response experiments showed that hydrogen was always formed faster from the surface than carbon dioxide. This principal effect was observed in transients obtained after different catalyst pretreatments with N 2 , with N 2 and H 2 O as well as with N 2 , H 2 O and H 2 . Pretreatment with H 2 O enhanced the transient responses of both H 2 and CO 2 . Separate chemisorption studies of H 2 , CO, and CO 2 indicated that CO 2 is a more abundant surface species than CO and H 2 . Based on the transient response experiments and the chemisorption studies a reaction mechanism was proposed, which involves water adsorption and decomposition steps, a reaction step between CO and surface hydroxyls giving H 2 and adsorbed CO 2 , and finally, a CO 2 desorption step. The surface reaction and CO 2 desorption steps were assumed to be rate determining. The stationary kinetics were described with a rate equation based on the rate determining steps, and the behaviour of the transient responses was explained with the proposed surface reaction mechanism.

Production of Activated Carbon from Cocoa (Theobroma cacao) Pod Husk

Activated carbons were obtained from cocoa pod husk using two different initial particle sizes (ranges 0.25 – 0.50mm and 0.50 – 1.00mm), three chemical activation agents (K2CO3, KOH and ZnCl2) and carbonization under nitrogen atmosphere during two hours at three different temperatures (500°C, 650°C and 800°C). The prepared activated carbons were characterized using Brunauer–Emmett–Teller (BET) and Langmuir surface areas, pore volume, average pore size, bulk density, moisture, ash content, and yield. The five best activated carbons were selected for further experiments according to the chemical activation agent used, high BET surface area, high pore volume and low ash content. Additionally, content of impurities, carbon content and FE-SEM micrographs were determined for these five best activated carbons. As adsorption tests were also carried out with these samples. Results of the experiments show that cocoa pod husk is a material that can be used to produce activated carbon by chemical activation and ZnCl2 showed to be the best chemical activation agent based on the highest BET surface area (780 m2/g in the best case) and pore volume (0.58 m3/g in the best case), the lowest ash content (6.14% in the best case), and the highest carbon content (86.1% in the best case), compared with others chemicals. Carbons activated by ZnCl2 are capable to adsorb As(V), getting As(V) removal levels up to 80% in less than 1 hour in the experimental conditions applied (initial pH 6-7, activated carbon concentration 0.1 g/l and 0.5 g/l, initial As concentration 100 ppb).

Development and verification of a simulation model for a non-isothermal water-gas shift reactor

Abstract A fixed-bed test reactor suitable for studying non-isothermal reaction kinetics was developed. The reactor allows axial and radial temperature measurem The water-gas shift reaction over a commercial iron-based catalyst was chosen as the subject of a case study. A non-isothermal reactor operating at tem with feed compositions corresponding to industrial conditions was used. A method of sequential regression analysis was applied to determine the kinetic conversion profiles of the bed. The experimental data could be fitted by a power-law type of reaction rate expression. The rate equation combined with successfully used to predict the fixed-bed behaviour within large temperature, concentration and space velocity intervals.

NOx abatement in lean exhaust gas conditions over metal substrated zeolite catalysts

Abstract Metal substrated ZSM-5 zeolites ion-exchanged with copper are effective catalysts in the elimination of nitrogen oxides from lean automotive exhaust gases when propene works as a reductant. Some co-cations improve the catalytic activity of Cu-ZSM-5. The critical temperature for the deactivation of Cu-ZSM-5 catalysts is around 700°C where the state of copper begins to change resulting in the decrease of the catalytic activity. The structure of the Cu-ZSM-5 zeolite collapses after thermal aging at temperatures above 800°C. However, the coexistence of chromium in the zeolite increases the thermal stability of Cu-ZSM-5 considerably.

Exposure assessment of particulates of diesel and natural gas fuelled buses in silico.

Lung deposition estimates of particulate emissions of diesel and natural gas (CNG) fuelled vehicles were studied by using in silico methodology. Particulate emissions and particulate number size distributions of two Euro 2 petroleum based diesel buses and one Euro 3 gas bus were measured. One of the petroleum based diesel buses used in the study was equipped with an oxidation catalyst on the vehicle (DI-OC) while the second had a partial-DPF catalyst (DI-pDPF). The third bus used was the gas bus with an oxidation catalyst on the vehicle (CNG-OC). The measurements were done using a transient chassis dynamometer test cycle (Braunschweig cycle) and an Electric Low Pressure Impactor (ELPI) with formed particulates in the size range of 7 nm to 10 microm. The total amounts of the emitted diesel particulates were 88-fold for DI-OC and 57-fold for DI-pDPF compared to the total amount of emitted CNG particulates. Estimates for the deposited particulates were computed with a lung deposition model ICRP 66 using in-house MATLAB scripts. The results were given as particulate numbers and percentages deposited in five different regions of the respiratory system. The percentages of particulates deposited in the respiratory system were 56% for DI-OC, 51% for DI-pDPF and 77% for CNG-OC of all the inhaled particulates. The result shows that under similar conditions the total lung dose of particulates originating from petroleum diesel fuelled engines DI-OC and DI-pDPF was more than 60-fold and 35-fold, respectively, compared to the lung dose of particulates originating from the CNG fuelled engine. The results also indicate that a majority (35-50%) of the inhaled particulates emitted from the tested petroleum diesel and CNG engines penetrate deep into the unciliated regions of the lung where gas-exchange occurs.