Determination of kinetics and controlling regimes for H2 oxidation on Pt/Al2O3 monolithic catalyst using high space velocity experiments
Determination of kinetics and controlling regimes for H2 oxidation on Pt/Al2O3 monolithic catalyst using high space velocity experiments
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DOI：
10.1016/j.apcatb.2010.12.030
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发表时间：
2011-02
影响因子：
22.1
通讯作者：
Saurabh Y. Joshi;Yongjie Ren;M. Harold;V. Balakotaiah
中科院分区：
文献类型：
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作者：
Saurabh Y. Joshi;Yongjie Ren;M. Harold;V. Balakotaiah
最近发展的标准[S.Y.Joshi，M.P.Harold，V.Balakotaiah，Chemical Engineering Science 65(2010)1729-1747]被用来表征在铂/氧化铝整体式催化剂上氢氧化过程中的各种控制机制(动力学、孔扩散和质量传递受控)。在很宽的温度和空间速度范围内测量了氢的转化率。在典型空速(10~4-105h−~1)下的实验表明，由于快速的催化动力学，在常温下可以实现完全转化。高活性使反应、涂层扩散和传质的相对重要性的分析变得复杂。高空速操作结合理论分析，能够有效地确定本征催化动力学，量化热量和质量传递系数，并确定由于反应、涂层扩散和外部质量传递过程所产生的阻力。具体地，我们考察了催化剂老化、空速和催化剂温度对区域转变的影响。分析表明，在较宽的温度范围内，老化催化剂以涂层扩散为主，而对于高分散新鲜催化剂，整体转变为90℃以上的传质控制区域。分析还表明，由于铂微晶的烧结导致催化剂的老化，不仅降低了指前因子，而且还降低了观察到的活化能。
Recently developed criteria [S.Y. Joshi, M.P. Harold, V. Balakotaiah, Chemical Engineering Science 65 (2010) 1729–1747] are used to characterize the various controlling regimes (kinetic, pore diffusion and mass transfer controlled) during H2oxidation on Pt/Al2O3monolithic catalyst. The hydrogen conversion was measured over a wide range of temperatures and space velocities. Experiments at typical space velocities (104–105h−1) revealed that complete conversion can be achieved at ambient temperature, a result of fast catalytic kinetics. The high activity complicates the analysis of the relative importance of reaction, washcoat diffusion and mass transfer. High space velocity operation with accompanying theoretical analysis enabled an efficient determination of the intrinsic catalytic kinetics, quantification of the heat and mass transport coefficients and determination of the resistances due to reaction, washcoat diffusion and external mass transport processes. Specifically, we investigated the effects of catalyst aging, space velocity and catalyst temperature on the regime transition. The analysis reveals that washcoat diffusion regime is dominant over a wide range of temperatures for the aged catalyst whereas the monolith transitions to a mass transfer controlled regime above 90°C for the high dispersion fresh catalyst. The analysis also reveals that the aging of the catalyst due to sintering of Pt crystallites not only reduces the pre-exponential factor but also the observed activation energy.