Yogi Wibisono Budhi

Ab initio Investigation of Hydrogen Atom Adsorption and Absorption on Pd(110) Surface

Ab initio investigation based on density functional theory is performed to determine the behavior of H atom diffusion in Pd(110) surface to the first and second subsurface layers. Potential energy surface is constructed to determine the local minima and activation barriers of H pathways. Contribution of the relaxation of surface atoms in the binding energies of H and activation barriers along the diffusion paths, as well as the zero point energy corrections are also included in this work. The binding energies of H in the second subsurface layer are lower compared to its binding energies in the first subsurface layer and this is attributed to the interaction of H with the surface atoms and the differences in interlayer spacing of the surface layers. Comments on the adsorbate induced Pd(110) (1×2) missing/adding-row reconstruction phenomenon is also given with reference to the observed results in this work as H is absorbed from the surface to the first subsurface layer.

Density Functional Theory Investigation on the Dissociation and Adsorption Processes of N2 on Pd(111) and Pd3Ag(111) Surfaces

The dissociation and adsorption processes of N2 on Pd(111) and Pd3Ag(111) surfaces are investigated using density functional theory (DFT). The dissociation of N2 molecule on Pd(111) is most efficient if its center-of-mass (CM) is fixed on top of Pd atom while allowing the N atoms to dissociate on the hollow sites [hcp hollow–top–fcc hollow (h–t–f) configuration] with an activation barrier of 5.94 eV. In Pd3Ag(111), N2 also prefers dissociating along the h–t–f configuration but the activation barrier is higher, 6.01 eV, and is attributed to the presence of Ag atom. The local density of states (LDOS) of the d-orbital of surface atoms shows that the presence of Ag had reduced the density of states in the region around the Fermi level which causes the higher activation barrier observed towards N2. Charge difference distribution also shows that there is a greater gain of charges of N2 from the surface atoms of Pd(111) surface which induces repulsion and resulting to the dissociation to individual N atoms. This further explains the easier dissociation and adsorption of N2 on Pd(111) as compared to Pd3Ag(111) surface.

Fluid dynamics and kinetic simulation for steam reforming of ethanol using a microchannel reactor

Proton Exchange Membrane Fuel Cell (PEMFC) has been recognized to be the potential source for future vehicles due to environmentally friendly. Supplying hydrogen for mobile vehicles is becoming of interest since storing compressed hydrogen in the bottle is not only dangerous but also energy consuming. One way to overcome the drawback is by performing the ethanol steam reforming in situ. In this way, microreactor offers the potential benefit to convert ethanol to hydrogen due to very fast mass and heat transfer. Fluid dynamics inside the microreactors and the kinetic aspects for ethanol steam reforming using Pt/Al2O3 catalyst were investigated with aim to determine the proper microreactor design having uniform fluid distribution and to study the influence of reaction temperature, fluid velocity, and reactor length. It was found that placing an obstacle inside the microreactors in certain position gave more uniform distribution of fluid flow. The reaction temperature and fluid velocity showed their influence on hydrogen productivity.

Catalytic oxidation of benzene using nano-CuO/γ-Al2O3 and commercial catalysts

Volatile organic compounds (VOC) such as benzene are among the most dangerous air pollutants emitted by chemical industry stacks, as they may contribute to environment and health issues. Lean catalytic oxidation of benzene has been considered as most proper method to abate it from the flue gas. This work developed nano-based copper oxide catalysts for lean oxidation of benzene. The aim of this study was to evaluate the activity performance of the nano-based copper oxide catalyst and compare to commercial catalyst. On the basis of the commercial catalyst, this study was also aimed to determine the reaction rate and its kinetic parameter. The oxidation of benzene was conducted in a fixed bed reactor at 300°C, 1 atm, and GHSV of 15,000 h−1. The concentration of benzene in the feed and product were measured using online gas detector (Cosmos Gas Detector). The catalyst activity of nano-based copper oxide catalysts showed 20-30% conversion of benzene, while for commercial catalyst showed 86%. The reaction rate determination for first order reaction of benzene indicated that the activation energy was 48 kJ/mol with Arrhenius constant of 3×104 s−1.

Dynamic operation of water gas shift reaction over Fe2O3/Cr2O3/CuO catalyst in Pd/Al2O3 membrane reactor

Hydrogen has been considered as promising energy carrier that can be produced from renewable resources, such as biomass through gasification. This process results in producer gas containing CO, CO2, H2, N2, and CH4. The conventional enhancement of hydrogen is typically conducted using several unit operations such as water gas shift reactor (WGSR) and separation unit such as Pressure Swing Adsorption (PSA). Process intensification offers a new method to integrate both WGSR and separation unit into single membrane reactor. This research aimed to investigate the influence of dynamic operation on membrane reactor performance. The steady state fixed bed reactor and membrane reactor were used as base case to judge the performance of dynamic membrane reactor. The water gas shift reaction over Fe2O3/Cr2O3/CuO was carried out at 350°C and 1 atm by varying the feed composition and gas residence time. The feed composition ratio of H2O/CO consisted of 2 and 3 on mole basis, while the gas residence times were 1.2 s and 2.3 s. The membrane reactor consists of shell and tube sides made of Pd/Al2O3 material with technical specification of 10 mm inner diameter, 20 μm Pd thickness supported by alumina, and 10 cm reactor length. The compositions of the feed gas and products were measured using gas analysers such CO gas detector (Bacharach PCA® 3) and H2 gas detector (Cosmos XP-3140). The dynamic operation was performed following the square wave perturbation of the feed gas at switching time of 15 s. The experiment results showed that increasing the feed composition ratio and gas residence time increased the conversion of CO and hydrogen production in the fixed bed reactor and membrane reactor. Higher production of hydrogen also improved the recovery of hydrogen in membrane reactor. The use of membrane reactor increased significantly the conversion of CO when compared to fixed bed reactor. Moreover, the dynamic membrane reactor would give much better performance in term of CO conversion and hydrogen recovery. The stability of the Pd/Al2O3 membrane reactor was proven for at least 10 h operation.

An eco-friendly preparation of cellulose nano crystals from oil palm empty fruit bunches

Cellulose Nanocrystals (CNCs) have attracted a lot of attention as one of the promising green nanomaterials because of their interesting properties such as low density, high mechanical properties, high surface area, high biocompatibility and low toxicity. However, sulphuric acids is generally used in conventional method to prepare CNCs which is highly corrosive and harmful to environment. Replacing sulphuric acid with Ammonium Persulfate (APS), which possess lower toxicity, are desirable from environment point of view. In this research, preparation of CNCs from Oil Palm Empty Fruit Bunches (OPEFB) as alternative raw materials and using APS is reported. Three kinds of method were carried out before applying APS solution: (i) without pre-treatment, (ii) with alkali pre-treatment and (iii) with alkali-chloride pre-treatment. White-colored sample with crystallinity reaching 78% (XRD result) and particle size ranging between 31-113 nm (DLS result) was obtained. Those results implied that there were potential existence of CNCs in the samples.

Process intensification of hydrogen production from Ethanol using microreactor

Hydrogen as potential energy source for Proton Exchange Membrane Fuel Cells (PEMFCs) possesses great challenge to replace gasoline due to their high calorific value. Hydrogen can be generated directly through Ethanol Steam Reforming (ESR) on portable reaction — microreactor. In this study, ESR was conducted by nine different variations of Pt/α- Al2O3 catalyst prepared by electroless plating method and four variations of reaction temperature between 270–315°C, atmospheric pressure, liquid feed flow of 0.5 mL/hour and molar feed composition of steam to ethanol 3:1. The result showed that the highest catalyst activity was reached at 300°C and 315°C. Time needed to reach stable hydrogen productivity at 285°C was longer than others. Average hydrogen productivity in stable condition varied between 6.31% (at 270°C) — 14.51% (at 300°C) of the highest hydrogen productivity achieved during six hours of ESR.