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.开孔泡沫催化剂床（open cell foam catalyst bed）结构可提升传热性能与气体流动特性，并最大化催化剂比表面积。该催化剂床结构实现的重量与尺寸缩减，使其可适配移动车辆等小型应用场景——此类场景对设备体积与重量均有严苛要求。较小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益于固定式发电装置的封装布局。该催化剂床可由单个整体式芯体（monolith core）制成，亦可由多个以圆盘形式堆叠的整体式芯体组合而成。现有发电机会产生大量一氧化碳，这通常是一种不受欢迎的副产物。优选方案中，耐火载体（refractory support）采用二氧化硅或硅酸盐，尤其以颗粒形式存在时更为适配——如此一来，下游区域所用的铜与铂族金属（platinum group metal）催化剂混合物，可通过物理混合负载铜催化剂的颗粒与负载铂族金属催化剂的颗粒轻松制备。该催化剂系统具备两项额外优势：其一，在甲醇氧化反应启动后不久，该反应便会脱离铂族金属催化剂，使下游区域降温，从而最大限度减少铂族金属催化剂的损耗，同时避免高温下通常会生成的一氧化碳；其二，若有未反应的氧气进入下游区域，其将被下游区域的铂族金属催化剂转化为水，从而避免产出的氢气中存在危险含量的氧气。部分氧化反应（partial oxidation reaction）会在混合物料进入催化剂系统的入口附近的热点（hot spot）区域快速启动。可通过调节混合物料送入系统的流速来调整该热点的精确尺寸与位置，优选将流速调整至使热点环绕混合物料的入口处。