Thermodynamic analysis of the production of hydrogen on platinum group metal catalyst surfaces

The open cell foam catalyst bed structure provides improved heat transfer, improved gas flow characteristics, and maximized catalyst surface area. The weight and size reductions achieved by using the catalyst bed construction are necessary for use in smaller applications such as in mobile vehicles, due to their smaller size and weight. Small size and weight also allow for rapid catalyst bed heat-up to operating temperatures which is a critical requirement for quick start capability necessary in most vehicle applications. The reduced size and weight will also benefit the packaging of stationary power plants. The catalyst bed can be formed from a single monolith core, or can be formed from a plurality of the monolith cores in the form of discs which are stacked one atop another. Existing generators produce significant quantities of carbon monoxide which is often an undesirable by-product. Preferably, the refractory support comprises silica or a silicate especially when in the form of granules so that the mixture of copper and platinum group metal catalysts used in the downstream zone can be easily made by physically mixing together granules supporting copper catalyst with granules supporting platinum group metal catalyst. The catalyst system offers two further advantages. Firstly, soon after the oxidation of methanol has been initiated, the methanol oxidation reactions move away from the platinum group metal catalysts allowing the downstream zone to cool so minimizing the losses of platinum group metal catalysts and the formation of carbon monoxide which would otherwise occur at high temperatures. Secondly, if any unreacted oxygen should arrive in the downstream zone, then it will be converted to water by the platinum group metal catalyst in the downstream zone so avoiding the possibility of dangerous amounts of oxygen being present in the hydrogen produced. The partial oxidation reaction quickly establishes itself in a hot spot adjacent the place of entry of the mixture into the catalyst system. The precise size and location of this hot spot can be adjusted by varying the flow rate at which the mixture is fed into the system and it is preferred to adjust the flow rate so that the hot spot surrounds the place of entry of the mixture.

开孔泡沫(open cell foam)催化剂床结构可提升传热性能、优化气体流动特性，并最大化催化剂比表面积。得益于该催化剂床结构实现的重量与尺寸缩减，其可适配诸如移动车辆这类对体积和重量有严苛要求的小型应用场景。小巧的体积与重量还可实现催化剂床快速升温至工作温度，这是多数车辆应用中快速启动功能的关键必要条件。缩减后的体积与重量同样有利于固定式发电装置的集成布局。该催化剂床既可由单个整体式芯体(monolith core)制得，也可由多个呈圆盘状的整体式芯体堆叠而成。现有发电机会产生大量一氧化碳，而该物质通常是不受欢迎的副产物。优选情况下，耐火载体(refractory support)可采用二氧化硅或硅酸盐，尤其当载体为颗粒状时，可通过物理混合负载铜催化剂的颗粒与负载铂族金属(platinum group metal)催化剂的颗粒，轻松制备下游区域所需的铜与铂族金属催化剂混合物。该催化剂系统还具备两项额外优势：其一，甲醇氧化反应启动后不久，便会脱离铂族金属催化剂，使下游区域温度降低，从而减少铂族金属催化剂的损耗，同时避免高温环境下一氧化碳的生成。其二，若有未反应的氧气进入下游区域，下游区域的铂族金属催化剂可将其转化为水，从而避免产出的氢气中混入过量氧气带来安全隐患。部分氧化反应会快速在混合物料进入催化剂系统的入口附近形成热点。该热点的精确尺寸与位置可通过调节混合物料的进料流速进行调控，优选方案为将流速调整至热点包裹住混合物料的入口位置。