Fabrication of an Effusive Molecular Beam Instrument for Surface Reaction Kinetics—CO Oxidation and NO Reduction on Pd(111) Surfaces

Abstract

A simple molecular beam instrument (MBI) was fabricated for measuring the fundamental parameters in catalysis such as, sticking coefficient, transient and steady state kinetics and reaction mechanism of gas/vapor phase reactions on metal surfaces. Important aspects of MBI fabrication are given in detail. Nitric oxide (NO) decomposition and NO reduction with carbon monoxide (CO) on Pd(111) surfaces were studied. Interesting results were observed for the above reactions and they support the efficiency of the MBI to derive the fundamental parameters of adsorption and catalysis. Sustenance of CO oxidation at 400 K is dependent mostly on the absence of CO-poisoning; apparently, CO + O recombination is the rate determining step £400 K. NO adsorption measurements on Pd(111) surface clearly indicating a typical precursor kinetics. Displacement of the chemisorbed CO by NO on Pd(111) surfaces was observed directly with NO + CO beams in the transient kinetics. It is also relatively easy to identify the rate-determining step directly from the MBI data and the same was demonstrated for the above reactions.

Porous thin films toward bridging the material gap in heterogeneous catalysis

“…MB experiments reported here was performed in a homemade 12 L capacity molecular beam instrument (MBI) 50 evacuated with a turbo-molecular drag pump to a base pressure of 2 × 10 −10 Torr. MBI is equipped with a quadruple mass spectrometer (Pfeiffer, HiQuad TM , QMG 700 with QMA 410, 1-128 amu) for the detection of all the relevant species of the reaction, a sputter ion gun for cleaning the sample surface, a molecular beam doser for the beam generation and a shutter to allow or block the beam at will.…”

“…MBI is equipped with a quadruple mass spectrometer (Pfeiffer, HiQuad TM , QMG 700 with QMA 410, 1-128 amu) for the detection of all the relevant species of the reaction, a sputter ion gun for cleaning the sample surface, a molecular beam doser for the beam generation and a shutter to allow or block the beam at will. More details are available in Refs 50 . CZ film deposited on a square Si disk (12 × 12 mm 2 ) was mounted on niobium sample holder, which is spot-welded with tantalum wires for heating and the temperature is measured by a Cr-Al (K-type) thermocouple, spot-welded to the backside of the sample holder.…”

Kinetics of Nitric Oxide Adsorption on Pd(111) Surfaces through Molecular Beam Experiments: A Quantitative Study

“…For accurate flux calibration and finding the F 0 , π, the flux from the doser and the fraction impinging on the crystal, respectively, we employed a standard procedure involving the condensation of cyclohexane at low temperature . The capacity factor π is determined to be about 0.45 as shown in the previous work . λ e is an effective pumping constant involving the pumping speed of the turbopump and the mass flux through it.…”

Surface science studies of selective catalytic reduction of NO: Progress in the last ten years

“…Studies of NO-CO reaction have been carried out on Pt(1 0 0) [30][31][32][33][34][35][36][37], Pt(1 1 1) [38], Pt(1 1 2) [39], Pd(1 0 0) [40], Pd(1 1 0) [41][42][43][44], Pd(1 1 1) [42,43,45,[46][47][48][49][50][51][52][53], Rh(1 0 0) [54], Rh(1 1 0) [54], Rh(1 1 1) [54][55][56][57][58][59][60][61][62][63][64][65], Ir(1 1 1) [66], Ir(2 1 1) [67], Cu(0 0 1) [68], Ag(1 1 1) [69], Pd/Cu(1 1 1) [48], Fe/Rh(1 0 0) [55], Rh/CeO x (1 1 1) [70], Pd/MgO(1 0 0) [71,72], Pt-Rh/TiO 2 (1 1 0) [73]...…”

“…NO decomposition and reduction with CO on Pd(1 1 1) surfaces were also studied [49]. Persistence of CO oxidation at 400 K is dependent mostly on the absence of CO-poisoning.…”